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MP Board Class 9th Maths Solutions Chapter 11 Constructions Ex 11.2

Question 1.
Construct a triangle ABC in which BC = 7 cm, B = ∠75° and AB + AC = 13 cm.
Solution:
BC = 7 cm
∠B = 15°
AB + BC = 13 cm.

Question 2.
Construct a triangle ABC in which BC = 8 cm, ∠B = 45° AB – AC = 3.5 cm.
Solution:
BC = 8 cm
∠B = 45°
AB – AC = 3.5 cm.

Question 3.
Construct a triangle PQR in which QR = 6 cm. ∠Q = 60° and PR – PQ = 2 cm.
Solution:
QR = 6 cm
∠Q =60°
PR – PQ = 2 cm

Question 4.
Construct a triangle XYZ in which ∠Y = 30°, ∠Z = 90° and XY + YZ + ZX = 11 cm.
Solution:
XY + YZ + ZX = 11 cm
∠Y = 30°
∠Z =90°

1. Draw a line segment BC =11 cm.
2. At B construct an angle of 30° and at C, draw angle of 90°.
3. Bisect these angles. Let the bisectors of these angles intersect atX.
4. Draw perpendicular bisectors AC of BX to intersect BC at Y and DZ of XC to intersect BC at Z.
5. Join XY and XZ. XYZ is the required D.

Question 5.
Construct a right triangle whose base is 12 cm and sum of its hypotenuse and other side is 18 cm.
Solution:
Steps of construction:

1. Draw \(\overline { BC } \) = 12 cm.
2. Construct ∠CBY = 90°.
3. From \(\overline { BY } \), cut off BX = 18 cm.
4. Join CX.
5. Draw PQ, the perpendicular bisector of CX, such that PQ meets BX at A.
6. JoinAC.

Thus, ABC is the required triangle.

MP Board Class 9th Maths Solutions

MP Board Class 9th Maths Solutions Chapter 10 Circles Ex 10.4

Question 1.
Two circles of radii 5 cm and 3 cm intersect at two points and the distance between their centres is 4 cm. Find the length of the common chord.
Solution:
Given
Let O and O₁ be the centre of bigger and smaller circle respectively
OA = OB = 5 cm
O₁A – O₁B = 3 cm
OO₁ = 4 cm

To find: AB.
Construction:
Join OA, OB, O₁A and O₁B join AB also.
In ∆OAO₁ and ∆OBO₁
OA = OB (Radii of a circle)
O₁A = O₁B (Radii of a circle)
OO₁ = OO₁ (Common)
so ∆OAO₁ = ∆OBO₁ (By SSS)
and so ∠1 = ∠2 (By CPCT)
In ∆OCA and ∆OCB,
OA = OB (Radii of a circle)
∠1 = ∠2 (Proved)
OC = OC (Common)
∆OCA = ∆OCB (By SAS)
so AC = BC (By CPCT)
and ∠ACO = ∠BCO (By CPCT)
∠ACO + ∠BCO = 180° (LPA’s)
⇒ ∠ACO + ∠BCO = 180°
2∠ACO = 180°
∠ACO = 90°
ar (OAO₁) = \(\frac{1}{2}\) x OO₁ x AC
= \(\frac{1}{2}\) x 4 x AC = 2ACcm² …..(i)
In ∆QAO₁, a = 5 cm, bc = 4 cm, c = 3 cm
12
s = \(\frac{5+4+3}{2}\) = \(\frac{12}{2}\) = 6 cm
s – a = 6 – 5 = 1 cm
s – b = 6 – 4 = 2 cm
s – c = b – 3 = 3 cm
ar(OAO₁) = \(\sqrt{s(s-a)(s -b)(s- c)}\).
= \(\sqrt{6x1x2x3}\)
= 6 cm² …..(ii)
From (i) and (ii), we get
2AC =6
AC = 3 cm
Now, AB = 2AC (∴ AC = BC)
= 2 x 3 = 6 cm.

Method II. By Construction:
Geometrically, AB is the diameter of the circle of radius 3 cm as it passes through centre O₁
AB = 2 x 3 = 6 cm.

Question 2.
If two equal chords of a circle intersect within the circle, prove that the segments of one chord are equal to corresponding segment of the other chord.
Solution:
Given
C (O, r) is a circle in which AB and CD are two equal chords which intersect at P.
To prove:
CP = BP and AP = DP.
Construction:
Draw OE and OF perpendiculars on AB and CD respectively. Join OP.
Proof:
In ∆OPF and ∆OPE,
OP = OP (Common)
OE = OF (∴ AB = CD)
∠F = ∠E (Each 90°)
∆OPF = ∆OPE (By RHS)
and so PE = PF …..(1) (By CPCT)
AB = CD (Given)

\(\frac{1}{2}\) AB = \(\frac{1}{2}\) CD
BE = CF
and AE = DF …..(2)
Adding (1) and (2), we get,
PE + AE = PF + DF
∴ AP = DP
Subtracting (1) and (2) we get,
BE – PE = CF – PF
∴ BP = CP

Question 3.
If two equal chords of a circle intersect within the circle, prove that the line joining the point of intersection to the centre makes equal angles with the chords.
Solution:
Given
AB and CD are two equal chords of a circle which intersect at E.
To prove:
∠1 = ∠2
Construction:
Draw OL ⊥ AB and OM ⊥ CD. Join OE.

Proof:
In ∆OLE and ∆OME,
OE = OE
OL = OM (∴ AB = CD)
∠L = ∠M (Each 90°)
∆OLE = ∆OME (By RHS)
and so∠1 = ∠2 (By CPCT)

Question 4.
If a line intersects two concentric circles (circles with the same centre) with centre O at A, B, C and D, prove that AB = CD. (see Fig. adjacent)

Solution:
Given:
C (O, r) and C (O, r) are two concentric circles.
To prove: AB = CD

Construction: Draw OP ⊥ AD.
Proof:
In circle I, AD is the chord and OP ⊥ AD.
AP = DP …(1)
In circle II, BC is the Chord and OP L BC.
∴ BP = CP …(2)
Subtracting (1) and (2), we get
AP – BP = DP – CP
AB = CD

Question 5.
Three girls Reshma. Salma and Mandip are playing a game by standing on a circle of radius 5 m drawn in a park. Reshma throws a ball to Salma, Salma to Mandip, Mandip to Reshma. If the distance between Reshma and Salma and between Salma and Mandip is 6 m each, what is the distance between Reshma and Mandip?
Solution:
Given:
OR = OM = 5 m and SR = SM = 6 m.
To find: MR.

Constrution:
Join OR, OM and OS. Draw ON ⊥ SR. In AORS and AOMS,
OS = OS (Common)
RS = MS (Given)
OR = OM (Given)
∆ORS = ∆OMS (By SSS)
and ∠1 = ∠2 (By CPCT)
SP = SP (Common)
SR = SM (Given)
∠1 = ∠2 (Proved)
∆SPR = ∆SPM (By SAS)
and so PR = PM (By CPCT)
and ∠3 = ∠4 (By CPCT)
∠3 + ∠4 = 180° (LPA’s)
2∠3 = 180°
∠3 = \(\frac{180^{\circ}}{2}\) = 90°
ar (∆OSR) = \(\frac{1}{2}\) x OS x PR …(i)
= \(\frac{1}{2}\) x 5 x PR
ON ⊥ SR
RN = \(\frac{1}{2}\) SR
(Perpendicular drawn from the centre of a circle to a chord bisects the chord)
= \(\frac{6}{2}\) = 3m
In ∆ONR ON² = \(\sqrt{O R^{2}-N R^{2}}\) (Using Pythagoras Theorem)
= \(\sqrt{5^{2}-3^{2}}\) = \(\sqrt{4^{2}}\) = 4m
ar (∆OSR) = \(\frac{1}{2}\) x SR x ON
= \(\frac{1}{2}\) x 6 x \(\frac{1}{2}\) x 4 = 12m² …..(ii)
From (i) and (ii), we get
PR = \(\frac{2×12}{2}\) = 4.8m
MR = 2 PR
= 2 x 4.8
= 9.6 m

Question 6.
A circular park of radius 20 m is situated in a colony. Three boys Ankur, Syed and David are sitting at equal distance on its boundary each having a toy telephone in his hands to talk each other. Find the length of the string of each phone.
Solution:
Given: OS = OA = 20 m and AS = SD = AD
To find: AS, SD and AD.
Construction:
Draw AE ⊥ SD. Join OS.
Let AS = SD = AD = 2x (say)

In equilateral ∠ASD, AE ⊥ SD
⇒ E is the mid-point of SD
SE = \(\frac{2x}{2}\) = x
In ∆AES, AS² = AE² + SE²
(2x)² = AE² + x²
4x² – x² = AE²
AE = \(\sqrt{3x^{2}}\) = \(\sqrt{3}\)
OE = AE – AO
= (\(\sqrt{3}\) – 20)m
In ∆OES, OS² = OE² + SE²
(20)² = [(\(\sqrt{3}\)x) 20]² + x²
400 = (\(\sqrt{3}\)x)² – 2 x \(\sqrt{3}\)x × 20 + (20)² + x²
= 3x² + 400 – 40\(\sqrt{3}\)x + x²
400 – 400 = 4x² – 40\(\sqrt{3}\)x
0 = 4x² – 40\(\sqrt{3}\)x
40\(\sqrt{3}\)x = 4x²
40\(\frac { 40\sqrt { 3 } }{ 4 } \) = x
x = 10\(\sqrt{3}\)m .
2x = 2 x 10\(\sqrt{3}\) = 20\(\sqrt{3}\)m
AS = SD = AD = 20\(\sqrt{3}\)m.

MP Board Class 9th Maths Solutions

MP Board Class 12th Chemistry Solutions Chapter 1 The Solid State

The Solid State NCERT Intext Exercises

Question 1.
Why are solids rigid ?
Answer:
Solids are rigid due to presence of strong inter- molecular forces between the constituent particles.

Question 2.
Why do solids have a definite volume ?
Answer:
In solids, the constituent particles are bonded together by strong attractive forces between them. By the increase or decrease of pressure, the intermolecular space remains unaffected. Thus, volume of solids is definite.

Question 3.
Classify the following as amorphous or crystalline solids : Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, poly vinyl chloride, fibre glass, copper.
Answer:
Amorphous solids: Polyurethane, teflon, cellophane, polyvinyl chloride, fibre glass.
Crystalline solids : Benzoic acid, potassium nitrate, copper.

Question 4.
Why is glass considered a super cooled liquid ?
Answer:
Like liquids, glass has tendency to flow but very slowly. Therefore, it is called super cooled liquid.

Question 5.
Refractive index of a solid is observed to have the same value along all directions. Comment on the nature of this solid. Would it show cleavage property ?
Answer:
Solid is amorphous because amorphous solids are isotropic in nature. No, it would not show the cleavage property.

Question 6.
Classify the following solids in different categories based on the nature of intermolecular forces operating in them : Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite, rubidium, argon, silicon carbide.
Answer:
Potassium sulphate : Ionic, Tin : Metallic, Benzene : Molecular (non-polar), Urea: Molecular (polar), Ammonia: Molecular (H-bonded), Water: Molecular (H-bonded), Zinc sulphide: Ionic, Graphite: Covalent or network, Rubidium: Metallic, Argon: Molecular (non-polar), Silicon carbide : Covalent or network.

Question 7.
Solid A is a very hard electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it ?
Answer:
Covalent solid.

Question 8.
Ionic solids conduct electricity in molten state but not in solid state. Explain.
Answer:
In Solid state, ions are not free therefore ionic solids are bad conductor. How¬ever, in molten state, the ions become free to conduct electric current.

Question 9.
What type of solids are electrical conductors, malleable and ductile ?
Answer:
Metallic solids, they are conductor due to the presence of free electron in them.

Question 10.
Give the significance of a ‘lattice point’.
Answer:
Each lattice point represents one constituent particle of the solid. This constituent particle may be an atom, a molecule (group of atoms) or an ion.

Question 11.
Name the parameters that characterise a unit cell.
Answer:
A unit cell is characterized by :

1. The dimensions along the three edges. These are represented by a, b, and c.
2. The angle between the edges. These are represented by α,β, and γ. The angle α is between b and c,β is between a and c and γ is between a and b (For diagram refer book).

Question 12.
Distinguish between (i) Hexagonal and monoclinic unit cells (ii) Face centred and end centred unit cells.
Answer:

1. For Hexagonal unit cell, a = b ≠ c, α = β = 90°, γ = 120°.
   For monoclinic unit cell a ≠ b ≠ c, α = γ = 90°, β = 90°.
2. Face centred unit cell has points at the comers as well as the centre of each face. It has 4 atoms per unit cell.
   End centred unit cell has points at all the comers and at the centre of any two opposite faces. It has 2 atoms per unit cell.

Question 13.
Explain, how much portion of an atom located at (i) corner and (ii) body centre of a cubic unit cell is part of its neighbouring unit cell ?
Answer:

1. 1/8th part of an atom located at comer belongs to neighbouring unit cell.
2. The atom at the body centre of a cubic unit cell is not shared by any other unit cell. Hence, it belongs fully to the unit cell.

Question 14.
What is the two-dimensional co-ordination number of a molecule in square close packed layer ?
Answer:
4.

Question 15.
A compound forms hexagonal close packed structure. What is the total number of voids in 0-5 mol of it ? How many of these are tetrahedral voids ?
Answer:
An atom in hep structure has three voids, one octahederal and two tetrahederal.
Number of atoms in 0-5 mol = 0.5 × 6.022 × 10²³ = 3.011 × 10²³
Total number of voids = 3 × 3.011 × 10²³ = 9.033 × 10²³
Number of tetrahedral voids = 2 × 3.011 × 10²³ = 6.022 × 10²³.

Question 16.
A compound is formed by two elements M and N. The element N forms ccp and atoms of M occupy 1/3rd of tetrahedral voids. What is the formula of the compound ?
Answer:
Since, N forms ccp arrangement, it will have 4 atoms in a unit cell.
Number of N atoms in unit cell = 4
For each atom, there are two tetrahedral voids so that there are 8 tetrahedral voids per unit cell.
No. of M atoms = \(\frac { 1 }{ 3 } \) × 8 = \(\frac { 8 }{ 3 } \)
Formula = M_8/3 N₄ or M₂N₃.

Question 17.
Which of the following lattices has the highest packing efficiency (i) simple cubic (ii) body centred cubic and (iii) hexagonal close packed lattice ?
Answer:
The packing efficiencies are :
Simple cubic = 52.4%
Body centred cubic = 68%
Hexagonal close packed = 74%
∴ Hexagonal close packed lattice has highest packing efficiency.

Question 18.
An element with molar mass 2.7 × 10^-2 kg mol^-1 forms a cubic unit cell with edge length 405 pm. If its density is 2.7 × 10³ kg m^-3, what is the nature of the cubic unit cell ?
Answer:
We know that Z = \(\frac{a^{3} \times \mathrm{N}_{\mathrm{A}} \times d}{\mathrm{M}}\)
Where a = 405pm = 405 x 10^-10
d = 2.7 × 10³ kg m^-3
M = 2.7 × 10^-2 kg m^-1
= 2.7g mol^-1
N_A = 6.203 x 10²³

Z =  4
∴ The element has fee (cep) unit cell.

Question 19.
What type of defect can arise when a solid is heated ? Which physical property is affected by it and in what way ?
Answer:
Vacancy defect is created when a solid is heated. This is because on heating some atoms or ions leave the lattice site completely. As a result the density of substance decreases.

Question 20.
What type of stoichiometric defect is shown by : (i) ZnS, (ii) AgBr.
Answer:
(i) ZnS, shows Frenkel defect due to large difference in size of ions.
(ii) AgBr, shows both Frenkel defect and Schottky defect.

Question 21.
Explain, how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it ?
Answer:
When a cation of higher valency is added as an impurity in the ionic solid, some of the site of the original cations are occupied by the cations of higher valency. For example, Sr⁺² in NaCl. Each Sr⁺² replaces two Na⁺ ions. It occupies the site of one Na⁺ ion and the other site remains vacant. The cation vacancies thus produced are equal in number to that Sr⁺² ions.

Question 22.
Ionic solids, which have anionic vacancies due to metal excess defect, develop colour ? Explain with the help of a suitable example.
Answer:
The anionic vacancies due to metal excess defect in ionic solids are occupied by free electrons to maintain the electrical neutrality. These impart colour by excitation of these electrons when they absorb energy from the visible light falling on the crystals. For example :
When NaCl is heated in presence of sodium vapours, Na⁺ ions are in excess, Cl^– ions leave their normal site and come to the surface. The vacant site of anion is occupied by electron forming F-centre. They absorb light from visible region and radiate complementary colour.

Question 23.
A group-14 element is to be converted into n-type semiconductor by doping it with a suitable impurity. To which group should this impurity belong ?
Answer:
n-type semiconductors are obtained by doping of a higher group impurity. Hence, to convert group 14 element to n-type semiconductor, it should be doped with a group 15 element.

Question 24.
What type of substances would make better permanent magnets, ferro-magnetic or ferrimagnetic ? Justify your answer.
Answer:
Ferromagnetic materials would make better permanent magnets than ferrimagnetic materials because in ferromagnetic solids, the magnetic moments of unpaired electrons spontaneously align themselves in same direction. However, in ferrimagnetic solids the magnetic moments of the domains are aligned in parallel and anti-parallel direction in unequal numbers.

The Solid State NCERT TextBook Exercises

Question 1.
Define the term ‘amorphous’. Give a few examples of amorphous solids.
Answer:
In non-crystalline solids constituent particles like atoms, molecules or ions do,not have a definite ordered structure. These do not have a definite geometry, thus they are also known as pseudo solid.
Example : Glass, rubber, plastic.

Question 2.
What makes a glass different from a solid such as quartz ? Under what conditions could quartz be converted into glass ?
Answer:
Quartz is a crystalline solid whereas glass is a amorphous solid. Quartz can be converted into glass by melting and rapid cooling.

Question 3.
Classify each of the following solids as ionic, metallic, molecular, network (covalent) or amorphous.
(i) Tetra phosphorus decoxide (P₄O₁₀)
(ii) Ammonium phosphate (NH₄)₃PO₄
(iii) SiC
(iv) I₂
(v) P₄
(vi) Plastic
(vii) Graphite
(viii) Brass
(ix) Rb
(x) LiBr
(xi) Si.
Answers:
Ionic : (NH₄)3PO₄, LiBr
Metallic : Brass, Rb
Molecular : P₄O₁₀,I₂,P₄
Network : Graphite, SiC, Si
Amorphous : Plastics.

Question 4.
(i) What is meant by the term ‘co-ordination number’ ?
(ii) What is the co-ordination number of atoms :
(a) In a cubic close packed structure ?
(b) In a body centred cubic structure ?
Answer:
(i) The number of nearest neighbours of a particle in its close packing is called its coordination number.
(ii) (a) 12, (b) 8.

Question 5.
How can you determine the atomic mass of an unknown metal if you know its density and the dimension of its unit cell ? Explain.
Answer:
Atomic mass (M)

Question 6.
‘Stability of a crystal is reflected in the magnitude of its melting points’, comment. Collect melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules ?
Answer:
Stability of a crystal depends on the force of attraction so : Higher the melting point of crystal, stronger the intermolecular force of attraction, hence greater is the stability of a crystal.

Melting point of the H₂O, C₂H₅OH, diethyl ether and methane given as below :

On the basis of melting point, the strength of the intermolecular forces between these molecules follows the order :
Water > Diethyl ether > Ethyl alcohol > Methane.

Question 7.
How will you distinguish between the following pairs of terms :
(i) Hexagonal close packing and cubic close packing ?
(ii) Crystal lattice and unit cell ?
(iii) Tetrahedral void and octahedral void ?
Answer:
(i) Refer to NCERT Text-Book (Close packing in crystals).

(ii) Crystal lattice :
Regular arrangement of the consti-tuent particle (atoms, molecules, or ions) of a crystal in three dimentional space.

Unit cell :
It is the smallest repeating unit in three-dimensional space, which is repeated again and again to give the complete lattice.

(iii)Tetrahedral void :

1. It is the open space between four touching spheres of two layers of atoms.
2. The radius of tetrahedral void relative to radius of sphere is 0-225.

Octahedral void :

1. It is the open space between six touching spheres of two layers of atoms.
2. The radius of octahedral void relative to radius of sphere is 0-414.

Question 8.
How many lattice points are there in one unit cell of each of the following lattice:
(i) Face centred cubic
(ii) Face centred tetragonal
(iii) Body centred.
Answer:
(i) In face centred cubic arrangement, number of lattice points are :
= 8 (at comers) + 6 (at face centres)
Lattice points per unit cell = 8 × \(\frac { 1 }{ 8 } \) + 6 × \(\frac { 1 }{ 2 } \) = 4.

(ii) In face centred tetragonal, number of lattice points are :
= 8 (at comers) + 6 (at face centres)
Lattice points per unit cell = 8 × \(\frac { 1 }{ 8 } \) + 6 × \(\frac { 1 }{ 2 } \) = 4

(iii) In body centred cubic arrangement, number of lattice points are :
= 8 (at comers) + 1 (at body centres)
Lattice points per unit cell = 8 × \(\frac { 1 }{ 8 } \) + 1 = 2

Question 9.
Explain:
(i) The basis of similarities and differences between metallic and ionic crystals.
(ii) Ionic solids are hard and brittle.
Answer:
(i) Metallic and Ionic crystal:
(a) Both metallic and ionic solids have high melting points.
(b) Ionic solids are hard and brittle but metallic solids are hard but not brittle, metals are malleable and ductile.
(c) Ionic solids are bad conductor but good conductor in a molten state and in solution. Metallic solids are good conductor in solid and liquid as well as in vapour state.
(d) Constituent units in ionic solids are cations and anions. In metallic solids, constituent units are Kernel (positively charged ions) surrounded by a sea of delocalized electrons.

(ii) Ionic crystals are hard because there are strong electrostatic forces of attraction among the oppositely charged ions. They are brittle because the ionic bond is non-directional.

Question 10.
Calculate the efficiency of packing in case of a metal crystal for:
(i) Simple cubic
(ii) Body centred cubic
Solution:
(i) Packing effiency of simple cube =

(ii) Packing efficiency in body centred cubic structure

(iii) Packing efficiency of face centred cubic structure

Question 11.
Silver crystallizes in fee lattice. If edge length of the cell is 4.077 × 10^-8 cm and density is 10-5 gem-3, calculate the atomic mass of silver.
Solution:

Z = 4 (fcc lattice), d = 10.5 gcm, N = 6.022 x 10, (a = 4.077 × 10^-8 cm)

Question 12.
A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body centre. What is the formula of the compound ? What are the co-ordination numbers of P and Q ?
Answer:
As atom Q are present at the 8 comers of the cube, therefore, number of atoms of Q in the unit cell = 8 × \(\frac { 1 }{ 8 } \) = 1.
As atoms P are present at the body centre, therefore number of atoms P in the unit cell = 1.
∴ Formula of the compound = PQ
Co-ordination number of each P and Q = 8.

Question 13.
Niobium crystallizes in body centred cubic structure. If density is 8.55 gem-3, calculate atomic radius of niobium using its atomic mass 93u.
Solution:
Density = 8.55 g cm^-3
Let, length of the edge = a cm
Number of atoms per unit cell, Z = 2 (bcc)
Atomic mass, M = 93 g mol^-1
density, d = \(\frac{\mathrm{Z} \times \mathrm{M}}{a^{3} \times \mathrm{N}_{\mathrm{A}}}\)

= 1.431 x 10^-10m = 0.143 nm

Question 14.
If the radius of the octahedral void is r and radius of the atoms in close packing is R, derive relation between r and R.
Solution:
Atoms covering the octahedral void from the top and below are not shown in the figure. Centre of octahedral void is C and its radius is equal to r. Atoms surrounding the voids are of radius R.

According to the figure,
Radius of atom surrounding the void BA = R
BC = Radius of void + Radius of outer atom
= R + r
∠ABC = 45°
in triangle ABC \(\frac {AB}{BC} \) = cos 45° = \(\frac{1}{\sqrt{2}}\) = 0.707
or \(\frac {AB}{BC} \) = 0.707
or 0.707 R + 0.707 r = R
or o.293 = 0.707r
\(\frac {r}{R} \) = \(\frac {0.293}{0.707} \) = 0.414

Question 15.
Copper crystallizes into a fee lattice with edge length 3.61 × 10^-8 cm. Show that the calculated density is in agreement with its measured value of 8.92 gcm^-3.
Solution:
We know that, d = \(\frac{\mathrm{Z} \times \mathrm{M}}{a^{3} \times \mathrm{N}_{\mathrm{A}}}\)
For fcc Z = 4, Atomic mass of copper = 63.5, a = 3.16 x 10^-8

= 8.96 g cm^-3
This value is close to measured value.

Question 16.
Analysis shows that nickel oxide has the formula NiO_0.98 O_1.00. What fractions of nickel exist as Ni²⁺ and Ni³⁺ ions ?
Solution:
Let there are x ions of Ni²⁺ and (0.98 – x) ions of Ni³⁺.
For electrical neutrality of the compound :
Total positive charge contributed by Ni²⁺ and Ni³⁺ ions = Total negative charge contributed by
O^2- ions
(+2 × x) + {+3 × (0-98 – x)} = 2
2x + 2.94 – 3x = 2
x = 0.94.
Thus, fraction of Ni²⁺ = \(\frac { 0.94 }{ 0.98 } \) = 0.96 or 96%
Fraction of Ni³⁺ = (1 – 0.96) = 0.04 or 4%.

Question 17.
What is a semiconductor ? Describe the two main types of semiconductors and contrast their conduction mechanism.
Answer:
Substance whose conductance likes in between that of metals (Conductors) and insulators are called semiconductors. There are two main types of semiconductors :

(i) n-type semiconductors : Silicon and germanium belong to group 14 of the periodic table and have four valence electrons each. In their crystals each atom forms four covalent bonds with its neighbours. When doped with a group 15 element like P or As, which contains five valence electrons, they occupy some of the lattice sites in silicon or germanium crystal. Four out of five electrons are used in the formation of four covalent bonds with the four neighbouring silicon atoms. The fifth electron in extra and becomes delocalised.

These delocalised electrons increase the conductivity of doped silicon (or germanium). Here, the increase in conductivity is due to the negatively charged electron, hence silicon doped with electron with impurity is called n-type semiconductor.

(ii) p-type semiconductors: Silicon or germanium can also be doped with a group 13 element like B, A1 or Ga which contains only three valence electrons. The place where the fourth valence electron is missing is called electron-hole or electron vacancy. An electron from a neighbouring atom can come and fill the electron hole, but in doing so it would leave an electron hole at its original position.

If it happens it would appear as if the electron hole has moved in the direction opposite to that of the electron that filled it under the influence of electric field, electrons would move towards the positively charged plate through electronic holes, but it would appear as if electron holes are positively charged and are moving towards negatively charged plate. This type of semiconductors are called p-type semiconductors.

Question 18.
Non-stoichiometric cuprous oxide, Cu₂O can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than 2:1. Can you account for the fact that this substance is a p-type semiconductor ?
Answer:
The ratio less than 2: 1 in Cu₂O shows that some cuprous (Cu⁺) ions have been replaced by cupric (Cu²⁺) ions. To maintain electrical neutrality, every two Cu⁺ ions will be replaced by one Cu²⁺ ion thereby creating a hole. As conduction will be due to presence of these positive hole, hence it is a p type semiconductor.

Question 19.
Ferric oxide crystallizes in a hexagonal close packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.
Solution:
Number of oxide (O^2-) ions = n
Number of octahedral voids = n
Number of Fe³⁺ ions = \(\frac { 2 }{ 3 } \) n
Fe³⁺ : O^2- = \(\frac { 2 }{ 3 } \)n : n
= 2 : 3
Formula, Fe₂O₃.

Question 20.
Classify each of the following as being either a p-type or an-type semiconductor :
(i) Ge doped with In
(ii) B doped with Si.
Answer:
(i) Ge belongs to group 14 and In belongs to group 13, therefore an electron-deficient hole is created and hence it is n-type semiconductor.
(ii) B belongs to group 13 and Si belongs to group 14, therefore there will be a free electron and hence it is n-type semiconductor.

Question 21.
Gold (atomic radius = 0.144 nm) crystallizes in a face-centred unit cell. What is the length of a side of the cell ?
Solution:
According to the question, r = 0.144 nm.
For fee structure:
Edge length (a) = 2\(\sqrt { 2 }\) × Radius of atom= 2 × 1.414 × 0.144
= 0.407 nm.

Question 22.
In terms of band theory, what is the difference :
(i) between a conductor and an insulator ?
(ii) between a conductor and a semiconductor ?
Answer:
(i) The energy gap between the valence band and the conduction band in an insulator is very large whereas in a conductor the energy gap is either very small or there is overlapping between valence band and conduction band.

(ii) In a conductor, the energy gap between the valence band and conduction band is very small or there is overlapping between valence band and conduction band. But in a semiconductor, there is always a small energy gap between them.

Question 23.
Explain the following terms with suitable examples :
(i) Schottky defect
(ii) Frenkel defect
(iii) Interstitials and
(iv) F-centres.
Answer:
(i) Schottky defect: This defect arises in the crystal when one cation and one anion is missing from their normal lattice site and as a result vacancies are created. Since, the number of missing positive ions is equal to the missing negative ions, the crystal as a whole is electrically neutral. Due to this defect, the density of the crystal decreases.

This defect generally occurs in strongly ionic compounds with high coordination number and where positive and negative ions are almost of similar sizes, e.g., NaCl and CsCl.

(ii) Frenkel defect: This defect is due to vacancy at a cation site. The cation leaves its correct lattice site and moves to another position between the two. Frenkel defects are common in ionic compound which possess low co-ordination number in which there is large difference between the size of positive and negative ions. As there is no absence of ions from the lattice the density remains the same, e.g. ZnS, AgCl.

(iii) Interstitial defect: When some constituent particles (atoms or molecules) occupy an interstitial site the crystal is said to have interstitial defect. This defect increases the density of the substance. Non ionic solids are example of this defect.

(iv) F-centres : Alkalihalides like NaCl and KCl show this type of defect when crystals of NaCl are heated in a atmosphere of sodium vapour the sodium atoms are deposited normal on the surface of the crystal. The Cl^– ions diffuse to the surface of the crystal and combine with Na atoms to give NaCl. This happens by the loss of electrons by sodium atoms to form Na⁺ ions. The released electron diffuse into the crystal and occupy anionic sites.

As a result crystal has now excess of sodium. The anionic sites occupied by unpaired electrons are called F-centres. They impart yellow colour to the crystal of NaCl. The colour results by excitation of these electrons when they absorb energy from the visible light falling on the crystals. Another examples are : LiCl, KCl etc.

Question 24.
Aluminium crystallizes in a cubic close packed structure. Its metallic radius is 125 pm.
(i) What is the length of the side of the unit cell ?
(ii) How many unit cells are there in 1.00 cm³ of aluminium ?
Solution:
(i) For a cubic close packed structure, length of the side of unit cell is related to radius.

Question 25.
If NaCI is doped with 10-3 mol % of SrCl₂, what is the concentration of cation vacancies ?
Solution:
We know that, doping of SrCl₂ to NaCI brings in replacement of two Na⁺ ions by each Sr²⁺ ions, but each Sr²⁺ occupies only one lattice point. This produces one cation vacancy.
Thus, doping of 10^-3 mole of SrCl₂ in 100 moles of NaCI.
NaCI will produce cation vacancies = 10³ mol
∵ 100 mole of NaCI will have cation vacancies after doping = 10^-3 mol
∴ 1 mole of NaCI will have cation vacancies after doping = \(\frac{10^{-3}}{100}=10^{-5}\) mol
Total cationic vacancies after doping = 10^-5 × NA
= 10^-5 × 6.023 × 10²³
= 6.023 × 10¹⁸ vacancies.

Question 26.
Explain the following with suitable examples :
(i) Ferromagnetism
(ii) Paramagnetism
(iii) Ferrimagnetism
(iv) Anti-ferromagnetism
(v) 12-16 and 13-15 group compounds.
Answer:
On the basis of magnetic properties solids are classified into following categories :
(i) Ferromagnetic : A substance which shows unusually large paramagnetism and shows permanent magnetism even in absence of a magnetic field is called ferromagnetic.
Examples : Fe, Co, Ni, CrO₂, Fe₃O₄, alnico (alloy of Al, Ni, Co, Fe and Cu)
A ferromagnetic substance if once magnetised remains magnetised permanently. Fer-romagnetism arises due to spontaneous alignment of magnetic moments (due to unpaired electrons) in the same direction.

(ii) Paramagnetic : A substance which is attracted by a magnetic field is called para-magnetic. Paramagnetism arises due to the presence of permanent dipoles due to unpaired electrons in atoms, ions or molecules.

Example : Cu⁺², Fe³⁺, TiO, CuO, O₂ etc.
(iii) Ferrimagnetic : A substance which shows fairly good paramagnetic character is called ferrimagnetic.
In ferrimagnetic substances the alignment of magnetic moments in opposite directions are not equal. As a result the substance attains a net magnetic moments, e.g. Fe₃O₄ isaferrimag- netic substance which on heating upto 850 K becomes paramagnetic.

(iv) Antiferromagnetic : A substance which shows much reduced paramagnetism than expected is called antiferromagnetic.
In antiferromagnetic substances the alignment of magnetic moments are equal and in opposite directions. Hence, the net magnetic moment is zero.
Examples: V₂O₃,Cr₂O₃,MnO,Mn₂O₃,MnO₂,FeO,Fe₂O₃,CoO, Co₃O₄,NiO

(v) 12-16 and 13-15 group compounds: Various types of compounds are formed by the mixture of elements of group 13 and 15 and group 12 and 16 whose average valency is like Ge and Si is 4. Of these specific compounds of group 13-15 are InSb, AlP and GaAs. Gallium arsenious are accelerated sensitive semiconductors. Semiconductors brought a revolutionary change in the manufacture of devices. ZnS, CdS, CdSe and HgTe are examples of compounds of group 12-16. Bonds of these compounds are not totally covalent and their ionic properties depend on the electronegativity of both the elements present.

The Solid State Other Important Questions and Answers

The Solid State Objective Type Questions

Question 1.
Choose the correct answer:

Question 1.
Due to Frenkel defect, density of ionic solids :
(a) Decreases
(b) Increases
(c) Does not change
(d) It changes.

Question 2.
In CsCl each Cl is surrounded by how many Cs :
(a) 8
(b) 6
(c) 4
(d) 2.

Question 3.
Frenkel defect is not shown by :
(a) AgBr
(b)AgCl
(c) KBr
(d) ZnS.

Question 4.
In NaCl crystal number of oppositely charged ions situated at equal distance are:
(a) 8
(b) 6
(c) 4
(d) 2.

Question 5.
Best conductor of electricity is :
(a) Diamond
(b) Graphite
(c) Silicon
(d) Carbon (Non-crystalline).

Question 6.
Which type of point defect is found in NaCI crystal or KCl crystal:
(a) Frenkel defect
(b) Schottky defect
(c) Lattice defect
(d) Impurity defect.

Question 7.
How many space lattices (Bravais lattice) can be obtained from various crystal systems:
(a) 7
(b) 14
(c) 32
(d) 230.

Question 8.
Diamond is a:
(a) H-bond solid
(b) Ionic solid
(c) Covalent solid
(d) Glass.

Question 9.
The Co-ordination number of Ca²⁺ ions in fluoride structure is :
(a) 4
(b) 6
(c) 8
(d) 3.

Question 10.
8 : 8 Co-ordination number is found in which compound :
(a) MgO
(b) Al₂O₃
(C) CsCl
(d) All of these.

Question 11.
Co-ordination number of body centred cubic cell is :
(a) 8
(b) 12
(c) 6
(d)4.

Question 12.
Density of unit cell is :

Question 13.
The number of tetrahedral voids in unit cell of cubic close packing :
(a) 4
(b) 8
(c) 6
(d) 2.

Question 14.
Intra-ionic distance of CsCl will be :
(a) a
(b) \(\frac { a }{ 2 } \)
(c) \(\frac{\sqrt{3}}{2} a\)
(d) \(\frac{2 a}{\sqrt{3}}\)

Question 15.
Number of atoms in body centred cubic unit cell is :
(a) 1
(b) 2
(c) 3
(d) 4

Question 16.
Which of the following is Bragg equation :
(a) nλ = 2Φ sin θ
(b) nλ = 2d sin θ
(c) nλ = sin θ
(d) \(n \frac{\theta}{2}=\frac{d}{2} \sin \theta\)

Question 17.
Constituents of covalent crystal is :
(a) Atom
(b) Molecule
(c) Ion
(d) All of these.

Question 18.
Number of Na atom present in the unit cell of NaCl crystal is :
(a) 1
(b) 2
(c) 3
(d) 4.

Question 19.
What type of magnetic substance are Fe, Co, Ni:
(a) Paramagnetic
(b) Ferromagnetic
(c) Diamagnetic
(d) Antiferromagnetic.

Question 20.
The correct example of Frenkel defect is :
(a) NaCI
(b) CsCl
(c) KCl
(d) AgCI.

Question 21.
Dry ice (solid CO₂) is a/an :
(a) Ionic crystal
(b) Covalent crystal
(c) Molecular crystal
(d) Metallic crystal.

Question 22.
Co-ordination number of Cs in CsCl:
(a) Like Cl i.e., 6
(b) Like Cl i.e., 8
(c) Unlike Cl i.e., 8
(d) Unlike Cl i.e., 6.

Question 23.
Structure of NaCl crystal:
(a) Tetragonal
(b) Cubic
(c) Orthorhombic
(d) Monoclinic.

Question 24.
Each Na⁺ ion in NaCl crystal is surrounded by :
(a) Three Cl^– ions
(b) Eight Cl^– ions
(c) Four Cl^– ions
(d) Six Cl^– ions.

Question 25.
For increasing of electro-conductivity in a solid crystal, mixing of impurities is known as:
(a) Schottky defect
(b) Frenkel defect
(c) Doping
(d) Electronic defect

Question 26.
Which type of lattice is found in KCl crystal:
(a) Face centred cubic
(b) Body centred cubic
(c) Simple cubic
(d) Simple tetragonal.

Question 27.
Number of atoms in a body centred cubic unit cell of a monoatomic substance is:
(a) 1
(b) 2
(c) 3
(d) 4.

Question 28.
Radius ratio limit for tetrahedral symmetry is :
(a) 0.155
(b) 0.414
(c) 0.732
(d) 0.225.

Question 29.
The defect produced due to a cation and an anion vacancy in a crystal lattice is known as:
(a) Schottky defect
(b) Frenkel defect
(c) Crystal defect
(d) Ionic defect.

Question 30.
If co-ordination number of Cs⁺ is 8 in CsCl then co-ordination number of Cl^– ion is :
(a) 8
(b) 4
(c) 6
(d) 12.

Answers:
1. (c), 2. (a), 3. (c), 4. (b), 5. (b), 6. (b), 7. (b), 8. (c), 9. (c), 10. (c), 11. (a), 12. (a), 13. (b), 14. (c), 15. (b), 16. (b), 17. (a), 18. (d),’ 19. (b), 20. (d), 21. (c), 22. (b), 23. (b), 24. (d), 25. (c), 26. (a), 27. (b), 28. (d), 29 (a), 30. (a).

Question 2.
Fill in the blanks :

1. The defect produced due to removal of a cation and an anion from a crystal lattice is called ………………..
2. If in a crystal lattice a cation leaves its lattice site and occupies a space in the interstitial site then the defect is called ……………….
3. The cause of electric conduction of NaCl in its molten state are its ………………..
4. Due to ……………….. defect the density of crystal decreases.
5. Total ……………….. types of crystal system are there.
6. ……………….. proposed the concept of atom for the first time.
7. The ratio of the cation and anion present in a crystal is known as ………………..
8. The process of adding small amount of impurities in an element or compound is called ………………..
9. Total 14 types of unit cells are there which are known as ………………..
10.  In NaCl crystal structure, co-ordination number of both Na⁺ and Cl^– ion is ………………..
11. ……………….. defect is found in ZnS and AgCl crystal.
12. Due to Schottky defect, density of crystal ………………..
13. In metallic solids, conductivity is due to the presence of …………..
14. Point defects are found in ………….. crystals.Substances which are attracted in magnetic field are called …………..
15. For a unit cell, if r = \(\frac{a}{\sqrt{8}}\) then it will be ………….. type of unit cell.
16. Conductivity of semiconductor ………….. on increasing temperature.

Answers:

1. Schottky defect
2. Frenkel defect
3. Free ions
4. Schottky
5. Seven
6. Kannad
7. Radius ratio
8. Doping
9. Bravais lattice
10. Six
11. Frenkel
12. Decreases
13. Free electron
14. Ionic
15. Paramagnetic substance
16. fcc
17. Increases.

Question 3.
Match the following

Answers:
1. (b)
2. (d)
3. (c)
4. (a)

Answers:
1. (c)
2. (d)
3. (a)
4. (b).

Answer:
1. (d)
2. (c)
3. (b)
4. (a).

Question 4.
Answer in one word / sentence :

1. Give two examples of metallic crystal.
2. Give two examples of covalent crystal.
3. Give two examples of ionic crystal.
4. What is the co-ordination number of F^– in CaF₂ ?
5. What type of crystal is SiC ?
6. What is the value of co-ordination number of hexagonal close packing structure ?
7. Write the formula of radius ratio.
8. What is the type of structure of NaCl crystal ?
9. Give an example of body centred cubic cell.
10. Give an example of a compound which has both Schottky and Frenkel type of defect.
11. Give two examples of amorphous or non-crystalline solid.
12. Write Bragg equation.
13. What is effect on the density of a substance or crystal due to Schottky defect ?
14. State the co-ordination number of CsCl and NaCl.
15. Write the formulae of two superconductors substance.
16. Give an example of Frenkel defect.
17. Give an example of superconductor.
18. Radius ratio of tetrahedral void is.

Answers:

1. Copper, Nickel
2. Diamond, Graphite
3. NaCl, NaNO₃
4. 4
5. Covalent
6. 12
7. 
8. Cubic
9. CsCl
10. AgBr
11. Glass,plastic,
12. nλ = 2d sin θ
13. Due to schottky defect, density of substance decreases
14. Co-ordination number of CsCl = 8 : 8, Co-ordination number of NaCl = 6:6
15. (i) λBa3- Cu₂O₇, (ii) Bi₂Ca₂Sr₂Cu₃O₁₀
16. AgCl
17. Ba_0.7K_0.3BIO₃
18. 0.225.

The Solid State Very Short Answer Type Questions

Question 1.
What are crystalline solids ? Crystalline solids are of how many types ?
Answer:
Solids in which the constituent particles like atoms, molecules or ions are in a definite order, with a definite geometry are known as crystalline solids.

Crystalline solids are of four types :

1. Ionic crystal
2. Covalent crystal
3. Molecular crystal
4. Metallic crystal.

Question 2.
Write the formula of density of unit cell.
Answer:

Question 3.
What is crystal lattice ?
Answer:
Geometry of a crystal in which unit cells are arranged in a definite order and forms a crystal like the shape of unit cell is known as crystal lattice.

Question 4.
What is a unit cell ?
Answer:
The smallest unit formed by the arrangement of constituent particles atoms, ions or molecules of a crystal in an ordered form is known as unit cell of the crystal.

Question 5.
Give two-two examples of each of the following :

1. Diamagnetic substance
2. Paramagnetic substance
3. Ferromagnetic substance
4. Antiferromagnetic substance
5. Ferrimagnetism.

Answer:

1. Diamagnetic substance – TiO₂, NaCl
2. Paramagnetic substance – Cu⁺², Fe⁺³
3. Ferromagnetic substance – Fe, Co
4. Antiferromagnetic substance – MnO₂, MnO
5. Ferrimagnetism – Fe₃O₄, Ferrite.

Question 6.
Write the structure and co-ordination number of the following:
(1) CsCl
(2) NaCl
(3) Zn.
Answer:
(1) CsCl – Structure : Cubic, Co-ordination number : 8.
(2) NaCl – Structure: Octahedral, Co-ordination number : 6.
(3) Zn – Structure : Tetrahedral, Co-ordination number : 4.

Question 7.
What makes a glass different from a solid such as quartz ? Under what conditions could quartz be converted into glass ?
Answer:
Glass is an amorphous solid in which constituent particles are orderly arranged in a short range order. Quartz is a crystalline form of silica in which SiO₄ units are orderly arranged in a long range order.
Quartz can be converted into glass by melting the glass and then cooling it rapidly.

Question 8.
Which are the seven fundamental crystal system on the basis of crystal geometry ?
Answer:
Seven types of crystal system are following:

1. Cubic
2. Tetragonal
3. Orthorhombic
4. Monoclinic
5. Hexagonal
6. Rhombohedral
7. Triclinic.

Question 9.
Write the names of different type of cubic system,
Answer:
Cubic system is of three types :

1. Simple cubic (see)
2. Body centred cubic (bcc)
3. Face centred cubic (fcc).

Question 10.
What is co-ordination number of Na⁺ and Cl^– in the structure of NaCl ?
Answer:
In NaCl structure each Na⁺ is surrounded by 6 Cl^– and each Cl^– is surrounded by 6 Na⁺ ions.
Thus, Co-ordination number of Na⁺ = 6
Co-ordination number of Cl^– = 6.

Question 11.
What is co-ordination number ? What is the effect of temperature and pressure on co-ordination number ?
Answer:
The number of neighbouring ions around the constituent particles of a crystal lattice is known as its co-ordination number. At high pressure co-ordination number increases and at low pressure it decreases.

Question 12.
What information is obtained by X-ray diffraction study of crystals ?
Answer:
By X-ray diffraction study of crystals, spacing between crystal planes of constituents particles of crystals is known.

Question 13.
What type of solids are electrical conductors : metallic or ductile ?
Answer:
Metallic solids.

Question 14.
Give the significance of a ‘lattice point’.
Answer:
Each lattice point represents one constituent particle of the solid. The constituent particle may be an atom, a molecule (group of atom) or an ion.

Question 15.
Refractive index of a solid is observed to have the same value along all directions. Comment on the nature of this solid. Would it show cleavage property ?
Answer:
As the solid has same value of refractive index along all directions, this means that it is isotropic and hence amorphous. Being an amorphous solid, it would not show a clean cleavage when cut with a knife. Instead it would break into pieces with irregular surfaces.

The Solid State Short Answer Type Questions

Question 1.
What is Schottky defect ?
Answer:
This type of defect is found in crystals in which both the cation and anion leave their normal lattice site and make their place vacant. In this defect, density decreases but r electrical neutrality is maintained. Like NaCl, CsCl etc.

Question 2.
What is radius ratio of ions ?
Answer:
Ratio of radii of cation and anion in any crystal is called radius ratio.

For example, in NaCl, ionic radii of Na⁺ and Cl- ions are 95 pm and 181 pm respectively.
Radius ratio in NaCl = \(\frac { 95 }{ 181 } \) = 0.52
Due to presence of other forces, in the crystal the observed value of radius ratio is less as in NaCl crystal it is 0414.

Question 3.
Describe briefly the structure of CsCl.
Answer:
It is AB type ionic crystal with body centred cubic structure. In this Cs⁺ ion in centre of cube and Cl^– ions at comers of cube (or vice versa). Co-ordination number of caesium chloride is 8 : 8 and radius ratio of Cs⁺ and Cl^– ions is 0.732.

In the unit cell of CsCl one Cs⁺ ion and one Cl^– ion are present.
Cs⁺ = 8 (at Centre) × 1 = 1
Cl^– = 8 (at corners) × \(\frac { 1 }{ 8 } \) = 1

Question 4.
Calculate the density of unit cell.
Answer:

If number of particles (atom, molecule, ions) of unit cell is Z and mass of each particle is m, then
Mass of unit cell = m × Z …….(1)
If molar mass of the substance is M, then mass of each particle :

Question 5.
Why is glass considered as super cooled liquid ?
Answer:
Glass is an amorphous solid. Like liquids it has tendency to flow, though very slowly. The proof of this fact is that the glass panes in the windows or doors of old buildings are invariably found to be slightly thicker at the bottom that at the top.

Question 6.
Ionic solids conduct electricity in molten state but not in solid state. Explain.
Answer:
In the molten state, ionic solids dissociate to give free ions and hence can conduct electricity. However in the solid state, as the ions are not free but remain held together by strong electrostatic forces of attraction, they cannot conduct electricity in the solid state.

Question 7.
What type of defect can arise when a solid is heated ? Which physical property is affected by it and in what way ?
Answer:
When a solid is heated, vacancy defect is produced in the crystal. This is because on heating some atoms or ions leave the lattice site completely, some lattice sites become vacant. As a result of this defect the density of the substance decreases because some atoms ions leave the crystal completely.

Question 8.
A compound consists of A and B exhibits cubic structure. A atoms are arranged at corners of cube while B are at the centre of faces. What will be the formula of the compound ?
Answer:
Atoms situated at corners are 8 A atoms which are shared by 8 cubes. So in the unit cell:
Number of A atom = 8 × \(\frac { 1 }{ 8 } \) = 1
B atoms are present in centre of 6 faces and each face is shared by two cubes
So number of B atoms = 6 × \(\frac { 1 }{ 2 } \) = 3
Formula of compound will be AB₃.

Question 9.
Prove that in face centred cubic (fee) structure, there are four atoms in an unit cell.
Answer:
Face Centred Cubic Structure : In this structure one atom is also situated in each face along with the corners of cube. The atom in each face is shared by two faces.
Thus, number of atom in each unit cell = 8 × \(\frac { 1 }{ 8 } \) (at 8 comers) + 6 × \(\frac { 1 }{ 2 } \) (at 6 faces)
= 1 + 3 = 4.

Question 10.
Write Bragg equation.
Answer:
Bragg equation is as follows : 2d sin θ = nλ.
Where, d = Distance between two consecutive planes in a crystal,
θ = Incident angle of X-rays
n = Simple whole number
λ. = Wavelength of X-rays.
By this distance d between the planes of the crystal is determined.

Question 11.
Name the parameters that characterise a unit cell.
Answer:
A unit cell is characterised by : (i) Its dimensions along the three edges a, b and c. These edges may or may not be mutually perpendicular
(ii) Angles between the edges, a, (between b and c), β (between a and c) and γ (between a and b). Thus, a unit cell is characterised by six parameters a, b, c, α, β and γ.

Question 12.
Window glass of old buildings appear milky. Why ?
Answer:
In day time, glass becomes hot and cools down at night. This way, the process of annealing takes place. Due to annealing in many years, glass develops crystalline property and window glass appear milky.

Question 13.
Common salt sometimes appear yellow instead of being colourless. Why ?
Answer:
In common salt, due to metal excess defect the anion Cl^– disappears from its lattice site but leaves an electron thereby which the crystal remains electrically neutral. A hole is formed at the vacant space of anion. This hole is known as F-centre. Due to this reason NaCl appear yellow.

Question 14.
With the increase in temperature, electrical conductivity of semiconductors increases. Why ?
Answer:
The energy gap between valence band and conduction band is less. Thus, with the increase in temperature, some electrons from the valence band jump to the conduction band due to which electrical conductivity increases with the increase in temperature.

Question 15.
Which of the following lattices has the highest packing efficiency :
(i) Simple cubic
(ii) Body centred cubic
(iii) Hexagonal close packed lattice ?
Answer:
Packing efficiency for simple cubic = 52-4%
Body centred cubic = 68%
Hexagonal close packed = 74%
Hence, Hexagonal close packed (hcp) has highest packing efficiency.

Question 16.
What type of stoichiometric defect is shown by (i) ZnS (ii) AgBr ?
Answer:
(i) ZnS shows Frenkel defect because its ions have a large difference in size.
(ii) AgBr shows both Frenkel and Schottky defects.

Question 17.
Explain how much portion of an atom located at: (i) Corner and (ii) Body centre of a cubic unit cell is part of its neighbouring unit cell ?
Answer:
(i) An atom at the corner is stand by eight adjacent unit cells. Hence, portion of the atom at the corner not belongs to one unit cell = \(\frac { 1 }{ 8 } \)
(ii) The atom at the body centre of a cubic unit cell is not stand by other unit cell. Hence, it belongs fully to the unit cell.

Question 18.
How can you determine the atomic mass of an unknown metal if you know its density and the dimension of its unit cell ? Explain.
Answer:
Let d – Density of the unit cell and volume of the unit cell = a3 (in case of cubic crystal)
Mass of an atom present in the unit cell

Question 19.
Stability of a crystal is reflected in the magnitude of its melting point. Comment. Collect melting point of solid water, ethyl alcohol,diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules ?
Answer:
Higher the melting point, greater are the forces holding the constituent particles together and hence greater is the stability.
Melting points of the substance are given below :

Question 20.
A group 14 element is to be converted into n-type semiconductor by doping it with a suitable impurity. To which group should this impurity belong ?
Answer:
n-type semiconductor means conduction due to the presence of excess of negative charged electrons. Hence, to convert group 14 element into n-type semiconductor, it should be doped with group 15 element.

Long Answer Type Questions

Question 1.
Give difference between crystalline solid and amorphous solid.
Answer:
Differences between Crystalline solid and Amorphous solid:

Crystalline solid:

1. Structure of crystalline solid are of definite geometrical shape.
2. In the internal structure, particle are arranged systematically.
3. Crystalline solids are solids in real sense.
4. Melting points of these compounds are sharp and definite.
5. These exhibit anisotropy.
6. Cooling curve are not continuous.
7. Crystalline solids possess less energy.

Amorphous solid

1. No any definite geometrical shape in the structure.
2. No any definite arrangement of particles in the internal structure. Amorphous solids are super cooled liquids.
3. Melting point of these compounds are not definite and sharp.
4. These exhibit isotropy.
5. Cooling curves are continuous.
6. Amorphous solids possess higher energy.

Question 2.
Distinguish between :
(i) Hexagonal and monoclinic unit cell
(ii) Face centred and end centred unit cell.
Answer:
(i) For hexagonal unit cell a = b ≠ c, α = β = 90°, γ = 120°
For monoclinic unit cell a ≠ b ≠ c, α = γ= 90°, β = 90°
(ii) A face centred unit cell has one constituent particle present at the centre of each face in addition to the particles present at the comers.
An end centred unit cell has one constituent particle each at the centre of any two opposite faces in addition to the particles present at the corners.

Question 3.
Give difference between Schottky and Frenkel defect.
Answer:
Differences between Schottky and Frenkel defect:

Schottky Defect:

1. Cation and anion completely leave their lattice sites.
2. Density of the crystal decreases by this defect.
3. This defect generally occur in ionic compounds with high co-ordination number where size cation and anion are nearly same.
4. No effect on dielectric constant.

Frenkel Defect:

1. Cation leave its normal lattice site and occupies the intestitial site.
2. No effect on the density of the crystal.
3. It is found in ionic compounds with low co-ordination number and where size of cation and anion differ largely.
4. Magnitude of dielectric constant increase.

Question 4.
What do you understand by imperfections in crystals ? What are the rea¬sons for imperfections ?
Answer:
It is generally supposed that arrangement of constituent particles in crystal struc¬ture is completely regular, but actually it is very hard to get a such complete ideal crystal. Crystal structures have many imperfections or defects. Reasons for these imperfections are following:
(i) Temperature: Crystal which have no imperfections or defects are known as ideal crystal. However such crystals exist only at absolute zero temperature because the energy of crystals at 0 K is minimum. At any temperature above 0 K, there are crystals which have some departure from complete order arrangement.

(ii) Presence of impurities : Sometimes presence of impurities causes disorder in regular arrangement of crystals which is responsible for imperfections and defects.

Question 5.
State the importance of radius ratio in crystal structure.
Answer:
Importance of radius ratio in crystal structure: Cations have tendency to get surrounded by maximum number of anions, hence larger be the size of cation greater will be its co-ordination number. We can understand this by taking examples of NaCl and CsCl. In NaCl, small sized Na⁺ has co-ordination number 6, while in CsCl large sized Cs⁺ ion has co-ordination number 8. Hence, radius ratio is closely related to co-ordination number.

Radius ratio, Co-ordination number and Structural arrangement

Question 6.
Ionic solids, which have anionic vacancies due to metal excess defect develop colour. Explain with the help of suitable example.
Answer:
Due to anion vacancies basic halides like NaCl, KCl etc., show this type of metal excess defect. Taking the example of NaCl, when its crystals are heated in presence of sodium vapour some chloride ion leave their lattice sites to combine with sodium to form NaCl. For this reaction to occur Na atoms lose electrons to form Na⁺ ions. The electron has released diffuse into the crystal to occupy the anion vacancies created by Cl^– ions. The crystal now has excess of sodium. The sites occupied by unpaired electrons are called F- centres. They impart yellow colour to the crystal because they absorb energy from the visible light and get excited.

Question 7.
What type of substances would make better permanent magnets : ferromagnetic or ferrimagnetic ? Justify your answer.
Answer:
Ferromagnetic substances make better permanent magnets. This is because the metal ions of a ferromagnetic substances are grouped into small regions called ‘domains’. Each domain acts as a tiny magnet. These domains are randomly oriented. When the substance is placed in a magnetic field all the domains get oriented in the direction of the magnetic field and a strong magnetic field is produced. This ordering of domains persists even when the external magnetic field is removed. Hence, the ferromagnetic substance becomes a permanent magnet.

Question 8.
How many lattice points are there in one unit cell of each of the following lattice:
(i) Face centred cubic
(ii) Face centred tetragonal
(iii) Body centred.
Solution:
(i) Lattice points in face-centred cubic lattice = 4.
(ii) Face centred tetragonal = 8 (at corners) + 6 (at the face centre) = 14.
However, particles per unit cell
= 8 × \(\frac { 1 }{ 8 } \) + 6 × \(\frac { 1 }{ 2 } \) = 1 + 3 = 4.
(iii) Lattice points in body centred cube
= 8 (at comers) + 1 (at the body centre)
= 9
However, particles per unit cell = 8 × \(\frac { 1 }{ 8 } \) + 1 = 2.

The Solid State Numerical Questions

Question 1.
A compound forms hexagonal close packed structure. What is the total number of voids in 0.5 mol of it ? How many of these are tetrahedral voids ?
Solution:
No. of atoms in the close packing = 0.5 mol
= 0.5 × 6.022 × 10²³
= 3.011 × 10²³
No. of octahedral voids = No. of atoms in the packing .
= 3.011 × 10²³
No. of tetrahedral voids = 2 × No. of atoms in the packing
= 2 × 3.011 × 10²³
= 6.022 × 10²³
Total No. of voids = 3.011 × 10²³ + 6.022 × 10²³
= 9.033 × 10²³.

Question 2.
A compound is formed by two elements M and N. The elements N forms ccp and atoms of M occupy l/3rd of the tetrahedral voids. What is the formula of the compound ?
Solution:
Suppose the atoms N in the ccp = n
∴ No. of tetrahedral voids = 2n
As 1/3rd of the tetrahedral voids are occupied by atoms M, therefore,
No of atoms M = \(\frac { 2n }{ 3 } \)
∴ Ratio of M : N = \(\frac { 2n }{ 3 } \) : n
Hence, the formula is M₂N₃

Question 3.
Structure of a solid AB is like NaCl. Radii of cation A is 100 pm, find out the radii of anion.
Solution:
For NaCl structure value of radius ratio (\(\frac{r^{+}}{r^{-}}\)) is in between 0.414 – 0.732.
Radius of cation is 100 pm.

Question 4.
The radii of A⁺ and B⁺ ions are 0.95 Å and 1.81 Å respectively. Find out the co-ordination number of A⁺.
Or,
The ionic radii of Na⁺ and Cl^– are 95 pm and 181 pm respectively.
What will be the co-ordination number of Na⁺?
Solution:
Radii of Na⁺ = 95 pm
Radii of Cl^– =181 pm
Radius ratio = \(\frac{r^{+}}{r^{-}}\) = \(\frac { 95 }{ 181 } \) = 0.524
Radius ratio is between 0.414 and 0.732. Thus, co-ordination number of Na⁺ or A⁺ will be 6.

Question 5.
Core length of a face centred cubic crystal is 400 pm calculate the density of element Atomic mass of element is 60.
Solution:
Density \((d)=\frac{Z \times M}{N_{0} \times a^{3}}\)
Where, Z = Number of atoms = 4, in face centred cubic structure.
M = Atomic mass = 60, N₀ = Avogadro number (6.023 × 10²³)
a = Core length (400 p.m.)

Question 6.
Silver crystallises in fee lattice. If edge length of the cell is 4.07 × 10^-8 cm and density is 10.5 g cm^-3, calculate the atomic mass of silver.
Solution:

Where d = Density of the material
a = Length of the edge of the cell
N_A = Avogadro number
Z = No. of atoms

∴ Atomic mass of silver = 107.08 g mol^-1.

Question 7.
Atomic mass of a face centred cubic (fee) is 60 g mol^-1 and its edge of its face is 400 pm. Determine the density of the element
Solution:
Volume of unit cell (a³) = (Length of edge)³
= (400 × 10^-12 m)³
= 64 × 10^-30 m³
= 64 × 10^-30 (10² cm)³
= 64 × 10^-24 cm³
Number of atoms in fee unit cell = 4

Question 8.
Structure of CuCl like ZnS is cubic. If density of CuCl is 3-4 g cm^-3, then determine the length of edge of the unit cell.
Solution:
ZnS has fee structure, thus same structure will be of CuCl. If length of edge of unit cell is a, number of atoms in fee is Z, molecular mass M and Avogadro number is N_A, then,

MP Board Class 12th Chemistry Solutions

MP Board Class 7th Science Solutions Chapter 18 Wastewater Story

Activities

Activity – 1
We have given one example of the use of clean water. You can add many more?

Answer:

Activity – 2
Locates an open drain near your home, school or on the roadside and inspect water flowing through it? Record color, odour and any other observation. Discuss with your friends and your teacher and fill up the following Table?
Table: Contaminant survey

Wastewater Story Text Book Exercises

Question 1.
Fill in the blanks:

1. Cleaning of water is a process of removing ……………………….
2. Waste – water released by houses is called ………………………
3. Dried ……………………… is used as manure.
4. Drains get blocked by …………………….. and ………………………..

Answer:

1. Contaminants
2. Sewage
3. Dung
4. Plastic, sludge.

Question 2.
What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas?
Answer:
Sewage is waste – water released by homes, hospitals, offices, industries and other users. It also includes rainwater that has run down the street during a heavy rain or storm. The water that washes off roads and roof tops carries harmful substances with it. Basically sewage is a liquid waste. Most of it is water, which has dissolved and suspended impurities which are called contaminants. That is why it is harmful to discharge untreated sewage in to rivers or seas.

Question 3.
Why should oils and fats be not released in the drain? Explain.
Answer:
Oils and fats should not be released in the drains because they harden the soil in the pipes and block them. Fats get clogged in the holes of the soil in the drain and block it. It does not allow the waste – water to flow and thus the whole sewer system is blocked.

Question 4.
Describe the steps involved in getting clarified water from waste – water?
Answer:
Treatment of waste – water involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates the waste – water.

1. Waste – water is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.

2. Water goes to a grit and sand removal tank. The speed of the incoming waste-water is decreased to allow sand, grit and pebbles to settle down.

3. The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the float able solids like oil and grease. Water so cleared is called clarified water.

4. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The bio gas produced in the process can be used as fuel or can be used to produce electricity.

5. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water. After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

Question 5.
What is sludge? Explain how it is treated?
Answer:
Sludge is the collected solid waste from the waste – water during the treatment in water treatment plant. Sludge is decomposed in a separate tank by the anaerobic bacteria. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organic matter and nutrients to the soil.

The treated water has a very low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Nature cleans it up further. Sometimes it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system.

Question 6.
Untreated human excreta is a health hazard? Explain?
Answer:
Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for wells, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include chlorea, typhoid, polio, meaningities, hepatitis and dysentery.

Question 7.
Name two chemicals used to disinfect water?
Answer:
Ozone, chlorine.

Question 8.
Explain the function of bar screens in a waste – water treatment plant?
Answer:
Bar screens clear the waste – water of all the physical impurities. Large waste objects like napkins, plastics, can sticks, rags etc. are removed from the waste – water through the bar screens.

Question 9.
Explain the relationship between sanitation and disease?
Answer:
Untreated human excreta is a health hazard. It may cause water pollution and soil pollution. Both the surface water and groundwater get polluted. Groundwater is a source of water for walls, tubewells, springs and many rivers. Thus, it becomes the most common route for water borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis and dysentery. That is proper sanitation is must to avoid some of the deadliest diseases.

Question 10.
Outline your role as an active citizen in relation to sanitation?
Answer:
As active citizen we should take care of our personal and environmental sanitation. We should make people around us, aware of the benefits of sanitation we should help the municipal corporations and gram panchayats to cover all the open drains and remove the unhygienic and disease causing substances thrown in open.

Question 11.
Here is a crossword puzzle: Good luck!

Across

1. Liquid waste products
2. Solid waste extracted in sewage treatment
3. A word related to hygiene
4. Waste matter discharged from human body.

Down

1. Used water
2. A pipe carrying sewage.
3. Micro – organisms which causes cholera.
4. A chemical to disinfect water.

Answer:

Question 12.
Study the following statements about ozone:

1. It is essential for breathing of living organisms.
2. It is used to disinfect water.
3. It absorbs ultraviolet rays.
4. Its proportion in air is about 3%.

Which of these statements are correct?

1. (a), (b) and (c)
2. (b) and (c)
3. (a) and (d)
4. All four.

Answer:

2. (b) and (c).

Extended Learning – Activities and Projects

Question 1.
Construct a crossword puzzle of your using the keywords?
Answer:

Across:

1. Mixing with air.
2. Decomposed product of leaves.
3. Does not read oxygen
4. Needs oxygen.

Down:

1. Necessary for hygiene
2. Solid waste
3. Pipes to carry sewage

Question 2.
Then and now: Talk to your grand parents and other elderly people in the neighbourhood? Find out the sewage disposal systems available to them. You can also write letters to people living in far off places to get more information. Prepare a brief report on the information you collected?
Answer:
Do yourself.

Question 3.
Visit a sewage treatment plant?
It could be as exciting and enriching as a visit to a zoo, a museum, or a park? To guide your observation here are a few suggestions?

Record in your notepad:
Place ……………….. Date …………………… Time
Name of the official at the plant ………………………. Guide/Teacher …………………………

1. The location of the sewage plant.
2. Treatment capacity.
3. The purpose of screening as the initial process?
4. How is air bubbled through the aeration tank?
5. How safe is the water at the end of the treatment? How is it tested?
6. Where is the water discharged after treatment?
7. What happens to the plant during heavy rains?
8. Is bio gas consumed within the plant or sold to other consumers?
9. What happens to the treated sludge?
10. Is there any special effort to protect nearby houses from the plant?
11. Other observations.

Answer:
Do with the help of your subject teacher.

Wastewater Story Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative :

Question (a)
This is not the cause of water pollution?
(a) Floods
(b) Rains
(c) Chemicals
(d) Open defecation.
Answer:
(b) Rains

Question (b)
To improve sanitation following new technique is being used?
(a) Vermi – processing toilets
(b) Sewer system
(c) Onsite sewage disposal
(d) Both (a) and (b).
Answer:
(d) Both (a) and (b).

Question (c)
Following should not be disposed off in the drains?
(a) Tissue Papers
(b) Excreta
(c) Oils and Fats
(d) Waste water.
Answer:
(c) Oils and Fats

Question (d)
Following process is not a part of waste – water treatment?
(a) Decomposition
(b) Grit and Sand Removal
(c) Evaporation
(d) Chlorination.
Answer:
(c) Evaporation

Question (e)
Polluted water causes disease likes –
(a) Hepatitis
(b) Typhopid
(c) Cholera
(d) Diarrhoea.
Answer:
(c) Cholera

Question (f)
In a public sewerage system, the largest sewers are –
(a) Filters
(b) Interceptors
(c) Waterways
(d) None of these.
Answer:
(b) Interceptors

Question 2.
Fill in the blanks:

1. …………………… bacteria is used to treat sludge.
2. Sewage is a liquid waste which causes water and soil
3. Waste – water is treated in a sewage treatment ………………………
4. …………………… and …………………….. are the products of water clarification.
5. By – products of waste – water treatment are sludge and ………………………
6. Addition of disease causing organisms in water is called water …………………….
7. …………………………… in open cause health hazards.
8. ……………………….. is used as manure.
9. To improve sanitation, low cost ……………………….. sewage disposal systems are being encouraged.
10. Adopting good sanitation practices should be our way of ……………………………….

Answer:

1. Anaerobic
2. Pollution
3. Plant
4. Sludge and bio gas
5. Bio – gas
6. Contamination
7. Defecation
8. Activated sludge
9. Onsite
10. Life.

Question 3.
Which of the following statements are true (T) or false(F):

1. Sewage contains pure water for drinking.
2. Used water is waste – water.
3. Waste – water could not be reused.
4. Open drain system is a breeding place for flies.
5. Manholes are located at every 50 m to 60 m in the sewerage.
6. Waste – water is passed through for screens.
7. Eucalyptus trees absorb all surplus waste – water rapidly and release pure water vapour into the atmosphere.

Answer:

1. False
2. True
3. False
4. True
5. True
6. True
7. True.

Wastewater Story Very Short Answer Type Questions

Question 1.
Define sewage?
Answer:
Sewage is water that contains waste products produced by human beings. It is also called waste water.

Question 2.
Which is the world water day?
Answer:
22nd March.

Question 3.
Which is proclaimed as the International Decade for action on water for life?
Answer:
United Nations proclaimed the period 2005 – 2015 as the international Decade for action on “Water for life”.

Question 4.
What do you mean by cleaning of water?
Answer:
Cleaning of water is a process of removing pollutants before it enters a water body or is reused.

Question 5.
What is sewage treatment?
Answer:
This process of wastewater treatment is commonly known as “Sewage Treatment”.

Question 6.
In how many steps sewage treatment divided?
Answer:
The sewage treatment in most cities involve two main steps primary and secondary treatment. Some cities also require an additional step called tertiary treatment.

Question 7.
What do you mean by primary treatment?
Answer:
The primary treatment removes the heaviest solid material from sewage. This process removes about half the suspended solids and bacteria in sewage. Sometimes chlorine gas is added to kill most of the remaining bacteria.

Question 8.
What do you mean by secondary treatment?
Answer:
The secondary treatment removes from 85% to 90% of the solids and oxygen consuming wastes remaining in sewage after it has undergone primary treatment. The most common methods of secondary treatment are the activated sludge process and the trickling filtration process.

Question 9.
Why should we plant eucalyptus along sewage ponds?
Answer:
These trees absorb all surplus waste – water rapidly and release pure water vapour into the atmosphere.

Question 10.
Write certain inorganic impurities in the waste – water?
Answer:
Metals, phosphates and nitrates.

Question 11.
Name certain disease causing micro – organism?
Answer:
Bacterias, Viruses etc.

Question 12.
Which process removes the solids like faces and other substances from the waste – water?
Answer:
Grit and sand removal tank.

Question 13.
How is sand, grit on pebbles settled down?
Answer:
Water goes to a grit and sand removal tank. The speed of the incoming waste-water is decreased to allow sand, grit and pebbles to settle down.

Question 14.
How is dry sludge used?
Answer:
Dried sludge is used as manure, returning organic matter and nutrients to the soil.

Question 15.
Who decomposes the sludge?
Answer:
Anaerobic bacteria decompose the sludge.

Question 16.
Which instrument is used to remove floatable solids from the waste – water?
Answer:
A skimmer is used to remove floatable impurities.

Question 17.
What helps to clean the clarified water?
Answer:
Aerobic bacteria helps to clean the clarified water.

Question 18.
Why is ozone and chlorine used?
Answer:
Ozone and chlorine is used to kill the bacteria etc. present in the clarified water.

Question 19.
Why is air pumped to clarified water?
Answer:
Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water.

Wastewater Story Short Answer Type Questions

Question 1.
Explain sewage?
Answer:
Waste water including human excreta which flows from our homes into the drains is called domestic sewage. This contains microbes which cause water – borne diseases. This waste water is often dumped into water bodies.

Question 2.
How is water polluted?
Answer:
Water is used various purposes in homes, industries and agriculture. When water is used for cleaning, bathing, washing, dying etc. it pollutes the water. Unwanted waste materials and chemicals etc get added in the water and this wastes the water.

Question 3.
What is done to improve sanitation?
Answer:
To improve sanitation, low cost onsite sewage disposal stem are being encouraged. Examples are septic tanks, chemical toilets, composting pits. Septic tanks are suitable for places where there is no sewerage system, for hospitals isolated buildings or a Luster of 4 to 5 houses.

Question 4.
What is vermi process toilet?
Answer:
A design of a toilet in which humans excreta is treated by earthworms has been tested in India. It has been found to be a novel, j low water – use toilet for safe processing of human waste. The operation of the toilet is very simple and hygienic. The human excreta is completely converted to vermi cakes resource much needed for soil.

Wastewater Story Long Answer Type Questions

Question 1.
How defection in open cause health hazards?
Answer:
Due to lack of proper sewage disposal system a large amount of people in India defecates in open. They use riverbeds, railway lines, fields and drains for this purpose. These excreta dries down and percolate in soil with rain water. It pollutes the ground water.

Excreate along river bed pollutes the river water. In this way water on the ground and under the ground get polluted. This polluted water contains the micro – organisms of various communicable diseases like cholera, typhoid, hepatitis and meaning it is dysentery etc.

Question 2.
Suggest some better house keeping practices?
Answer:

1. Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats dog the soil pores redunt. Its effectiveness in filtering water. Oil and fats should he thrown in the dustbin.

2. Chemicals like paints, vents, insecticides, motor oil, medicines may kill microbes it help purity water. So they should not be thrown in the drain.

3. Used ten – leaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin. These waste choke the drains. They do not allow free flow of oxygen. This hampers the degradation process.

Question 3.
What is the composition of sewage?
Answer:
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities. nutrients, saprotrophic and disease causing bacteria and other microbes.

1. Organic impurities:
Human faces, animal waste, oil, urea (urine), pesticides, herbicides, fruit and vegetable waste, etc.

2. Inorganic impurities:
Nitrates, phosphates, metals. Nutrients Phosphorus and nitrogen.

3. Bacteria:
Such as which cause cholera and typhoid.

4. Other microbes:
Such as which cause dysentery.

Question 4.
How is sewage treated?
Answer:
Domestic sewage should be treated before being discharged into the river. Sewage is treated by first separating the solid material by sedimentation and filtration. Compressed air is then passed through the liquid which is then chlorinated to kill micro – organisms. The solid matter separated from sewage can be used to generated bio gas which can be used as fuel. The sludge that is left can be used as manure in the fields to grow organic foods.

Question 5.
What are the different ways in which solid waste can be disposed off?
Answer:
The different ways are as:

1. Domestic wastes like fruit and vegetable waste, leftover food, leaves of potted plants can be converted into compost and used as manure.
2. Most of the solid waste is buried in low lying areas to level uneven land. This is called landfill.
3. Wastes coming from industries such as metals can be recycled and used again.
4. Broken plastic articles like plastic bags, buckets, bowls, cups, plates, etc. can be melted and remolded to make new articles.
5. The waste disposal on a large scale is done by the municipality of a city using incinerators. The solid waste is burnt at high temperature. Ash is removed from time to time.

Question 6.
Explain sewage treatment plant.
Answer:
Sewage is water that contains waste products by human beings. It is also known as waste water. In fact sewage comes from the sinks and toilets of homes, restaurants, factories and office buildings. The sewage mainly consists of dissolved material that cannot be seen and bits of such solid matter as human waste and ground up rubbish.

It also contains harmful chemical and disease producting bacteria. Most sewage ultimately goes into lakes, rivers and oceans. However, in many western nations, the sewage is treated in some way before it goes into the waterways as a semi – clear liquid called effluent. Most methods used to treat sewage convert organic sewage into inorganic compounds viz. nitratres, sulphates and phosphates. Some of these compounds serve as food for algae. As the algae decay using excess of oxygen from water, the fish and plants in water will ultimately die.

Question 7.
Explain rural sewerage system?
Answer:
Many rural areas not served by public sewers. In such areas, most home owners use septic tanks to treat their sewage. These tanks are concrete or steel containers buried underground at home and buildings. Sewage flows into a septic tank through a pipe connecting the tank with a building.

Solids in the sewage sink to the bottom of the tank as sludge or float to the surface as scum. Effluent then flows from the tank into a system of pipes with open joints that allow sewage effluent to be gradually distributed into the soil. The soil bacteria then destroy the remaining organic material in the influent.

In a septic tank, bacteria in the sewage attack and digest the sludge and scum. The digestion process changes most to the wastes into gas and a harmless substance called humus. The gas then escapes into the air. The humus in the tank should be pumped our periodically and taken to a sewage treatment plant.

Question 8.
Explaining urban sewerage system?
Answer:
In a public sewerage system, the largest sewers, known as interceptors, carry the sewage to a wastewater treatment plant. The sewage treatment in most cities involves two main steps, primary treatment and secondary treatment. Some cities also require an additional step called tertiary treatment. At a treatment plant, sewage first passes through a screen that traps the largest pieces of matter. It then flows through a grit chamber, where heavy inorganic matter, such as sand, settles down.

The liquid next flows into a large primary sedimentations tank. Many suspended solids sink to the bottom of this tank and form a muddy material called sludge. Grease floats to the surface, where it is removed by a process called skimming. The effluent is then released into waterways.

Primary treatment removes bout half of the suspended solids and bacteria in sewage. Sometimes chlorine gas is added after primary or secondary treatment to kill most of the remaining bacteria. The secondary treatment removes about 85 to 90 percent of the solids and oxygen consuming wastes remaining in sewage after it has undergone primary treatment.

Question 9.
Explain the most common methods of secondary treatment in urban sewerage system?
Answer:
The most common methods of secondary treatment are:

1. The activated sludge process.
2. The trickling filtration process.

In case of activated sludge process, the influent from the primary sedimentation tank flows into a second tank called an aeration tank. The useful bacteria move through the liquid and change the organic matter into less harmful substances. The liquid then flows into a final sedimentation tank, where the sludge settles down to the bottom.

The influent is then discharged into waterways. In case of trickling filtration process, the filters are filled with crushed rocks. As sewage is distributed over the rocks, it reacts with slime that develops on the rocks. The slime contains useful bacteria that change organic material in the sewage into less harmful substances. These substances are removed in a final sedimentation tank, where they fall to the bottom as sludge.

Sometimes tertiary treatment is also used after primary and secondary treatment to produce purer effluent. The tertiary treatment methods include chemical treatment, microscopic screening, radiation treatment, etc. Tertiary treatment makes effluent safer to discharge into waterways.

MP Board Class 7th Science Solutions

MP Board Class 7th Science Solutions Chapter 5 Acids, Bases and Salts

Acids, Bases and Salts Intext Questions

Question 1.
Can I taste all substances to find their taste?
Answer:
No, we should not taste unknown substances. They could harm us.

Question 2.
I am not getting the same result when using solid baking soda on dry litmus paper. Why?
Answer:
Make a solution of baking soda and then try.

Activities
Activity 1
Let us recall tastes of some edible substances listed in table. If you have not tasted any of these substances taste it now and enter the result in the given table.
Answer:

Activity 2
Mix some water with lemon juice in a plastic cup/ tumbler/ test tube. Put a drop of the above solution on a strip of the red litmus paper with the help of a dropper.

• Is there any change in colour.
• Repeat the same exercise with the blue litmus paper.
• Note down if there is any change in colour.

Perform the same activity with the following substances:
Tap water, detergent solution, aerated drink, soap solution, shampoo, common salt solution, sugar solution, vinegar, baking soda solution, milk of magnesia, washing soda solution, lime water. If possible make solutions in distilled water. Record your observations as in table.
Answer:

Activity 3
Take a tablespoonful of turmeric powder. Add a little water and make a paste.
Make turmeric paper by depositing turmeric paste on blotting paper/filter paper and drying it. Cut thin strips of the yellow paper obtained.

• Put a drop of soap solution on the strip of turmeric paper.
• What do you observe
• Similarly test the solutions listed in table and note down your observations.

Answer:
The turmeric turns red.

Acitivity 4
Collect some China rose (Gudhal) petals and place them in a beaker. Add some warm water. Keep the mixture for some time till water becomes coloured. Use the coloured water as an indicator. Add five drops of the indicator to each of the solutions given in table:

Acids, Bases and Salts Text book Exercises

Question 1.
State ditterences between acids and bases?
Answer:
Differences between acids and bases:
Acids:

1. Acids are substances which contain one or more replaceable hydrogen atoms.
2. All acids are sour in taste.
3. All acids turn blue litmus red.
4. Acids are compounds that contain hydrogen.
5. Acids react with metal to form salts and release hydrogen gas.

Bases:

1. Bases are substances which have one or more replaceable hydroxyl group (OH).
2. Bases are bitter in taste and slippry in touch.
3. Bases turn red litmus blue.
4. Bases are compound which have hydroxyl group.
5. Bases react with acids to form salts.

Question 2.
Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer:
Basic.

Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
Litmus solution is extracted from lichens. It is used as indicator.

Question 4.
Is the distilled water acidic/basic/neutral? How would you verify it?
Answer:
The distilled water is neutral.

Put a drop of distilled water on a strip of the red litmus paper with the help of a droper. We observe that colour of the litmus paper is not change. The solutions which do not change the colour of either red or blue litmus are knwon as neutral solutions. These substances are neither acidic nor basic.

Question 5.
Describe the process of neutralisation with the help of an example?
Answer:
The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water
Example: Following reaction:
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H₂O)

Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false:

1. Nitric acid turn red litmus blue. (T/F)
2. Sodium hydroxide turns blue litmus red. (T/F)
3. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
4. Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
5. Tooth decay is caused by the presence of a base. (T/F)

Answer:

1. False (F)
2. False (F)
3. True (T)
4. True (T)
5. False (F).

Question 7.
Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve tire drinks on the demand of customers. One customer wants acidic drind, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Answer:

1. He can decide by the use of indicator.
2. It the sample of drink turns red litmus blue, it is basic. It it turns blue litmus red, it is acidic.
3. It it does not effect litmus, then it is neutral.

Question 8.
Explain why?

1. An antacid tablet is taken when you suffer from acidity.
2. Calamine solution is applied on the skin when an ant bites.
3. Factory waste is neutralised before disposing it into the water bodies.

Answer:
1. Our stomach contains hydrachloric acid. It help us to digest food. But too mcuh of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

2. Ant injects an acid (i.e., formic acid) during bite which cavses the burning sensation. Calamine solution is basic in nature. It neutralises the acid and relives us from the pain.

3. Factory wastes contain both acidic and basic substances. If they are allowed to flaw into the water bodies, they are harmful for orgainsms living in water. So the factory wastes are neutralised by adding basic substances.

Question 9.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Answer:
Turmeric solution turns red in contact with bases. It is not affected by acids and neutral substances. So, first we will identify the base.

Now, the base is taken and turmeric is added. It will turn red. Then, one of the solutions is added to it gradually. If the solution turns yellow again, the added liquid is hydrochloric acid because it neutralises the base. Otherwise the added liquid is sugar solution.

Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The nature of the solution is neutral, because the solutions which do not change the colour of either red or blue litmus are known as neutral solution. These substances are neither acidic nor basic.

Question 11.
Consider the following statements:

1. Both acids and bases changes colour of all indicators.
2. If an indicator gives a colour change with an acid, it does give a change with a base.
3. If an indicator changes colour with a base, it does not change colour with an acid.
4. Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

1. All four
2. (a) and (d)
3. (b) and (c)
4. only (d)

Answer:
4. only (d).

Extended Learning – Activities and Projects:

Question 1.
Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet root. Explain how it works?
Answer:
Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beet root over the message.

Question 2.
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table?
Answer:
Do with the help of your subject teacher.

Question 3.
Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner?
Answer:
Do yourself.

Question 4.
Visit a doctor. Find out the medicines, he prescribes to treat acidity Ask him how acidity can be prevented?
Answer:
Do yourself.

Acids, Bases and Salts Additional Important Questions

Objective Type Questions

Question 1
Choose the correct alternative

Question (i)
Bases are –
(a) Sour in taste
(b) Sweet in taste
(c) Bitter in taste
(d) None of the above.
Answer:
(c) Bitter in taste

Question (ii)
Blue litmus turns red by –
(a) Sodium
(b) Sodiujn sulphate
(c) Bitter in taste
(d) Qattstic potash.
Answer:
(c) Bitter in taste

Question (iii)
Which one of the following oxides will react with acids to salt and water –
(a) CO
(b) SO₂
(c) SO₃
(d) CuO.
Answer:
(d) CuO.

Question (iv)
Which of the following is a mineral acid –
(a) Acetic acid
(b) Citric acid
(c) Tartaric acid
(d) Nitric acid.
Answer:
(d) Nitric acid.

Question (v)
Which is the common name of sodium bicarbonate –
(a) Caustic soda
(b) Washing soda
(c) Blue vitriol
(d) Baking soda.
Answer:
(d) Baking soda.

Question (vi)
For diluting acid –
(a) Water is added to acid.
(b) Acid is added to water.
(c) Acid is boiled after adding water.
(d) Acid is boiled before adding water.
Answer:
(c) Acid is boiled after adding water.

Question (vii)
……………. is used for white – washing in house.
(a) Sodium hydroxide
(b) lime stone, calcium hydroxide
(c) blue vitriol
(d) lime water and ash.
Answer:
(b) lime stone, calcium hydroxide

Question (viii)
Nausadar is –
(a) Acid
(b) Alkali
(c) Salt
(d) Indicatior
Answer:
(c) Salt

Fill in the blanks:

1. Acetic acid is present in while is present ………….. While …………. is present in lemon.
2. Magnesium burns in air to form …………. which is ………….. oxide.
3. The chemical formula of slaked lime is ……………..
4. Acids are …………….. in taste.
5. The gas which escapes out from many aerated soft drinks is …………..
6. ………….. are slippery in touch.
7. Bases turn ………….. litmus to …………..
8. In a neutralisation reaction an ………….. and an ………….. combine to form a salt and water.
9. The solution formed by reacting P₂ O₅ with H₂O turns ………….. litmus ……………
10. Methyl orange is a good ……………

Answer:

1. Vinegar, citric acid
2. Magnesium oxide, basic
3. Ca₂, (OH)₂
4. Sour
5. CO₂
6. Bases
7. Red, blue
8. Acid, alkali
9. Blue, red
10. Indicator.

Question 3.
Which of the following statements are true (T) or false (F):

1. Acids have a bitter taste.
2. Bases have a bitter taste.
3. Bases react with carbonate to liberate carbon dioxide.
4. Copper does not reach with tamarind (imli) water.
5. Sulphuric acid is c.’led ‘King of chemicals’.
6. Orange juice turns blue litmus red.
7. Alum (Phitkari) acts as a antacid.
8. Soaps are salts of fatty acids.
9. Copper sulphate is used as a preservative in pickels. Potassium chloride is a salt of sulphuric acid.

Answer:

1. False
2. True
3. False
4. True
5. True
6. True
7. False
8. True
9. False
10. False.

Question 4.
Paheli brought the following paheli (riddle) for you.

1. Coffee is brown
2. And bitter in taste
3. Is it an acid
4. Or a base
5. Don’t give the answer
6. Without any test
7. You are in the dark With its taste

Answer:
Acidic.

Acids, Bases and Salts Very Short Answer Type Questions

Question 1.
Which acid is present in our stomach?
Answer:
Hydrochloric acid in small amount is present in our stomach.

Question 2.
What will you do if some acid is split on the table?
Answer:
We will sprinkle some base on the table to neutralise the effect of the acid.

Question 3.
Why antacids tablests are used to reduce acidity of the stomach?
Answer:
Sometimes due to spicy food the concentration of hydrochloric acid increases in the stomach. This causes acidity. To reduce it some harmless bases are used like milk of magnesia [Mg (OH)₂] and aluminium hydroxide, which balance the excess of acids. These are solid in the form of tablets called antacids.

Question 4.
What are mineral acids? Give two examples.
Answer:
The acids which are capable of forming hydrogen ions, when dissolved in water are mineral acids. For example, HCl, HNO₃, H₂SO₄ (Hydrochloric acid, Nitric acid, Sulphuric acid). In other words, mineral acids are strong acids. These acids are called mineral acids because these are prepared from minerals.

Question 5.
What are organic acids? Give two Examples.
Answer:
Organic acid are soured milk, lemon, green mangoes and karvanda are sour tasting. All of them contain some naturally occurring acids. Such acids are found in animals and plant materials. They are known as organic acids.
Examples: Lactic acid, Citric acid, Vinegar, Formic acid.

Question 6.
What do you understand by concentrated and dilute acids?
Answer:
Concentrated acid:
The acids which are prepared by dissolving in water, are known as concentrated acid.

Dilute acid:
The acid which are prepared by dissolving in excess amount of water are known as dilute acids.

Question 7.
Name the gas obtained when a metal carbonate reacts with an acid?
Answer:
When metal carbonate reacts with acids they give carbon dioxide gas.

Question 8.
What will happen if blue litmus paper is soaked in orange juice?
Answer:
It change into red colour.

Question 9.
State one characteristic property of all acids. Is dry hydrogen chloride gas an acid?
Answer:

1. Acids have a sour taste.
2. Acids turn blue litmus red.
3. Acids react with metal to evolve hydrogen gas.
   2HCl + Mg → MgCl₂ + H₂
   Yes, hydrogen chloride is an acid.

Question 10.
A solution turns red litmus paper into blue. What does this indicate about the chemical nature of the solution?
Answer:
The solution which turns red litmus paper blue is basic in nature. The substance which turns red litmus paper blue is known as alkalies.

Question 11.
Classify the following chemicals in acids and bases:
KON, HNO₃, Ca(OH)₂, LiOH, CH₃COOH, HCOOH, Mg(OH)₂, NaOH, H₂SO₄, HCl
Answer:
Acids:
HNO₃, H₂SO₄, HCl.

Bases:
KOH, Ca(OH)₂, LiOH, CH3COOH, HCOOH, Mg(OH)₂, NaOH.

Acids, Bases and Salts Short Answer Type Questions

Question 1.
You are given hydrochloric acid solution, sodium hydroxide solution and water in three different bottles. How will you check which bottle has which compound?
Answer:
Take three pieces of blue litmus paper. Put one piece of blue litmus paper into each of these solutions. That bottle which turns blue litmus red contains hydrochloric acid. Take three pieces of red litmus paper. Put one piece of red litmus paper into each of these solutions. That bottle which turns red litmus blue contains sodium hydroxide (base).

Question 2.
How can you test the presence of acid in a substance?
Answer:
Acids can be tested in any substance by the following methods:

1. Take a drop of the dilute solution of the substance on the tips of your tongue. If it taste sour, it is acid.
2. Place a blue litmus paper in the solution. If the colour changes to red, acid is present.

Example: 2Na + 2HCl → 2NaCl + H₂

Question 3.
What are indicators? Name two acid – base indicators.
Answer:
The substance which are used to identify whether a substance is an acid or base is called indicators. For example, litmus solutions give red colour with acids and blue colour with bases. Therefore, litmus is used as indicator. Substances wrhich given differnet colours with acid and base are called acid – base indicators.
Example:

1. Methyl orange
2. Phenolpthalein

Question 4.
State the colour of dry litmus paper when placed in separate samples of dilute sulphuric acid, moist ammonia gas, moist chlorine, sodium hydroxide, lemon juice, vinegar and water into which sulphur dioxide gas has been bubbled for some time?
Answer:

Question 5.
Why are acids not stored in metal containers? Containers/ vessels made from which material are safe to store acids?
Answer:
All the acids react with metals. They react vigorously and slowly with metals according to their nature. So, the acids are not stored in metal containers. Vessels made from glass or cermics are considered safe for strong acids.

Question 6.
Which acids are present in following substance:

Answer:

1. Citric acid
2. Acetic acid
3. Lactic acid
4. Oxalic acid
5. Tartaric acid.

Question 7.
Why does colour of blue vitriol change when heated?
Answer:
When we blue vitriol heated it changes into white vitriol and water.

Question 8.
Write one use of each of the following compounds?

1. Vinegar
2. Methly orange
3. Alum
4. Sulphuric, acid
5. Sodium hydroxide.

Answer:

1. In pickles and jam for preserving it in good condition for long duration.
2. As a indicator.
3. In purifying water.
4. In purifying pertroliujn products.
5. In purifying pertrolium products.

Question 9.
What are acid salts? Give two examples?
Answer:
Acid salt:
When a strong acid is neutralised by a weak base, then a salt is formed, such type of salt is called acid salt.
For example:
H₂SO₄ + 2NH₄OH → (NH ) SO₄ + 2H₂O
HCl+ NH₄OH → NH₄Cl + H₂O

Question 10.
Complete the following equations:

1. NaOH + H₂SO₄ → ……………. + H₂O
2. H₂CO₃ + NaOH → ……………. + H₂O
3. HNO₃ + KOH → ……………. + H₂O
4. Mg (OH)₂ + 2HCl → ……………. + 2H₂O

Answer:

1. NaOH + H₂SO₄ → Na₂SO₄ + H₂O
2. H₂CO₃ + 2NaOH → Na₂CO₃ + 2H₂O
3. HNO₃ + KOH → KNO₃+ H₂O
4. Mg (OH)₂ + 2HCl → + MgCl₂ + 2H₂O

Question 11.
Name the gas obtaines when a metal carbonate reacts with an acid?
Answer:
When metal carbonate reacts with acids they give carbon dioxide gas.
For example.

Question 12.
Differentiate between bases and alkalies by giving suitable examples of each?
Answer:
Bases:
Bases are the compound which have one or more hydroxyl group (OH) in their molecule.
Examples: NaOH, Ca(OH)₂, KOH etc.

Alkalies:
Water soluble bases are called alkalies.
Examples: Sodium hydroxide, potassium hydroxide and calcium hydroxide.

Question 13.
What is a neutralisation reaction? Give two examples.
Answer:
The reaction of an acid with an alkali and vice – versa to form salt and water is called neutralisation reaction.
For examples:

Question 14.
How is salt obtained from sea – water?
Answer:
The seas are great sources of salts. A litre of a water contains about 35 grams of salts. Sodium chloride is the main salt. The sea water is trapped in shallow called lagoons and is allowed to evaporate in sunlight to white solid crystal of salts. These crystals are processed and packed to send to markets.

Question 15.
What are the uses of weak alkalies?
Answer:

1. Ammonia is a weak alkali. It is used for the manufacture of fertilizers.
2. Ammonia is also used for the production of wood pulp and organic chemicals.
3. It is also used for making synthetic fibres such as nylon and nitric acid, which are used for the preparation of synthetic cloth.
4. Calcium hydroxide is used in the manufacture of bleaching powder.

Question 16.
Tabulate the some hydrated salts with their chemical formulae and colour?
Answer:
Some hydrated salts:

Question 17.
Name some common acid and alkali indicators?
Answer:

Acids, Bases and Salts Long Answer Type Question

Question 1.
What are acids? Write their properties.
Answer:
Acids are substances which contain one or more replaceable hydrogen atoms. Its properties are:

1. 1. All acids are sour in taste.
   2. All acids turn blue litmus red.
   3. Acids are compounds that contain hydrogen e.g., H₂SO₄, HCl etc.
   4. Acids are compounds which form hydronium ion (H₃O⁺) in aqueous (water) solution.
      Example:
      

1. Acids react with metal to form salts and release hydrogen gas.
   Example: 2Na + 2 HC1 → 2NaCl + H₂
   
2. Acids react with carbonates and bicarbonates to give carbon dioxide gas.
   Example:
   

Question 2.
What are bases? Write down its properties.
Answer:
Bases are substances which have one or more replaceable hydroxyl group (OH).
The various properties of bases are:

1. Bases are bitter in taste and slippery in touch.
2. Bases turn red litmus blue.
3. Bases are compound which have hydroxyl group.
4. All bases give hydroxyl ion into aqueous solutions.
   
5. Bases react with acids to form salts.
   Example: NaOH + HCl → NaCl + H₂O

Question 3.
What are the uses of mineral acids in industry?
Answer:
The uses of mineral acids in industry are:

1. Concentrated sulphuric acid, nitric acid and hydrochloric acid are used in a large number of metallurgical operations, manufacture of fertilizers and preparations of large number of industrial chemicals.

2. Hydrochloric acid is used for removing the deposits from inside the boilers. This process is known as descaling.

3. One of the mineral acid, hydrochloric acid (HCl) present in our stomach helps in digestion of food.

4. Nitric acid (HNO₃) is used by goldsmiths for cleaning gold and silver ornaments.

Question 4.
Distinguish clearly between the following terms by giving suitable examples:

1. Organic acid and mineral acid.
2. Base and alkali.

Answer:
1. Organic acid:

• Organic acid contains COOH functional group.
• These acids are weak.
• These acids are present in humans and plants.
• They are less corrosive and are used in food ingradients.
  Examples: Ethanoic acid, lactic acid, citric acid.

Mineral acid:

• Mineral acid contains hydrogen ions (H⁺).
• These acids are strong.
• These acids are prepared by mankind.
• They are corrosive in nature and have industrial use.
  Examples: Hydrochloric acid, sulphuric acid, nitric acid.

2. Base:

• Bases are the compound which have one or more hydroxhyl group (OH) in their molecule.
• All alkalies are bases
• Bases are insoluble in water.
  Examples: NaOH, Ca(OH)₂, KOH

Alkali:

• Water soluble bases are called alkalies.
• All bases are not alkalies.
• Alkalies are soluble in water.
  Examples: Sodium hydroxide potassium hydroxide and calcium hydroxide.

Question 5.
Write any three most common salts used in daily life and write their uses?
Answer:
Most common salts used in daily life are:
1. Washing Soda: Na₂CO₃.10H₂O.
Uses:

• It is used in laundary.
• It is used to prepare other compounds such as glass, caustic soda and detergent poweders.

2. Baking Soda: NaHCO₃
Uses:

• It is used in baking powder.
• It is used as medicine to reduce acidity of the stomach.
• It is used in fire extinguisher.

3. Potash alum or phitkari:
K₂SO_4.Al₂(SO₄)₃24H₂O
Uses:

• It is used to purify water.
• It is used after shave to stop the bleeding from cuts.

MP Board Class 7th Science Solutions

MP Board Class 9th Maths Solutions Chapter 9 Areas of Parallelograms and Triangles Ex 9.3

Question 1.
In Fig. given below E is any point on median AD of a ∆ABC. Show that ar (ABE) = ar (ACE).

Solution:
Given.
E is any point on median AD of ∆ABC.
To prove
ar (ABE) = ar (ACE)

Proof:
In ∆ABC, AD is the median
ar (ABD) = ar(ACD) ….(1)
In ∆EBC, ED is the median
∴ ar (BDE) = ar (CDE) ….(2)
Subtracting (2) from (1), we get
ar (ABD) – ar (BDE) = ar (ACD) – ar (CDE)
ar (ABE) = ar (ACE)

Question 2.
In a triangle ABC, E is the mid-point of median AD. Show that ar (BED) = \(\frac{1}{4}\) ar (ABC).

Solution:
Given
E is the mid point of – median AD of ∆ABC.
To prove:
ar (BED) = \(\frac{1}{4}\) ar (ABC)
Proof:
In ∆ABC, AD is the media
ar (ABD) = \(\frac{1}{2}\) ar (ABC) …..(1)
In ∆ABD, BE is the median

ar (BED) = \(\frac{1}{2}\) ar (ABD)
= \(\frac{1}{2}\) [\(\frac{1}{2}\) ar (ABC)]
= \(\frac{1}{4}\) ar (ABC)

Question 3.
Show that the diagonals of parallelogram divide it into four triangles of equal area.
Solution:
Given.
ABCD is a parallelogram.
To prove:
ar (AOB) = ar (BOC) = ar (COD) = ar (AOD)

Proof:
In ∆ABC, OA is the median
∴ ar (AOB) = ar (AOD) …..(1)
In AABC, BO is the median
∴ ar (AOB) = ar (BOC) …..(2)
In ABCD, CO is the median
ar (BOC) = ar (COD) …(3)
From (1), (2) and (3), we get
ar (AOB) ar (BOC) = ar (COD) = ar (AOD)

Question 4.
In Fig. given below, ABC and ABC are two triangles on the same base AB. If line – segment CD is bisected by AB at O, show that ar (ABC) = ar (ABD).

Solution:
Given.
∆ABC and ∆ABD have a common base AB.
OC = OD
To prove
ar (ABC) = ar (ABD)

Proof:
As OC = OD,
O is the mid-point of CD
In ∆ACD, O is the median
ar (AOC) = ar(AOD)
In ABCD, BO is the median
ar (BOC) = ar (BOD)
Adding (1) and (2), we get
ar (AOC) + (BOC) = ar (AOD) + ar (BOD)
ar (ABC) = ar (ABC)

Question 5.
D, E and F are respectively the mid-points of the sides BC, CA and AB of a AABC. Show that

1. BDEF is a parallelogram.
2. ar (DEF) = \(\frac{1}{2}\) ar (ABC)
3. ar (BDEF) = \(\frac{1}{4}\) ar (ABC).

Solution:
D, E, F are the mid points of sides BC, CA and AB of ∆ABC.
To prove:

1. BDEF is a parallelogram.
2. ar (DEF) = \(\frac{1}{4}\) ar (ABC)
3. ar (BDEF) = \(\frac{1}{2}\) ar (ABC)

Proof:
In ∆ABC, F is the mid-point of AB, E is the mid point of AC.
∴ FE ∥ BC and FE = – BC (By MPT)
⇒ FE ∥ BD and FE =BD

1. BDEF is a ∥^gm
Similarly CDFE and AEDF are ∥^gm
In parallelogram BDEF, DF is the diagonal
∴ ax (BDF) = ar (DEF)
[In a ∥^gm diagonal divides it into 2∆s of equal areas]
Similarly, In ∥^gm CDFE, DE is a diagoilal …(1)
ar (CDE) = (DEF) …(2)
In ∥^gm AEDF, FE is a diagonal
ar (AEF) = ar (DEF) …(3)
From (1), (2) and (3), we get
ar (BDF) = ar (CDF) = ar (AEF) = (DEF) …(4)

2. ar (ABC) = ar (AEF) + ar (ADF) + ar (CDE) + ar (DEF)
ar (ABC) = 4 ar (DEF) [Using (4)]
ar (DEF) = \(\frac{1}{4}\) ar (ABC)

3. ar (BDEF) = ar (BDF) + ar (DEF)
ar (BDEF) = 2ar (DEF) [∴ ar (BDF) = ar (DEF)]
= 2 x \(\frac{1}{4}\) ar (ABC) = \(\frac{1}{2}\) ar (ABC)

Question 6.
In the Fig. diagonals AC and BD of quadrilateral ABCD intersect at O such that OB = OD. If AB – CD, then show that:

1. ar (DOC) = ar (AOB)
2. ar DCB = ar (ACB)
3. DA ∥ CB or ABCD is a parallelogram.

[Hint: From D and B, draw perpendiculars to AC.]

Solution:
Given
ABCD is a quadrilateral in which OB = OD and AB = CD.
To prove:

1. ar (DOC) = ar (AOB)
2. ar (DCB) = ar (ACB)
3. DA ∥ CB or ABCD is a ∥^gm

Construction:
Draw DE and BF perpendicular from point D and B on AC.
Proof:
1. In ∆OED and ∆OFB
∠1 = ∠2 (V.O.A.’s)
OD = OB (given)
∠E = ∠F (each 90°)
∆ OED = ∆ OFB (by AAS)
and so DE = BF (by CPCT)
In ∆DEC and ∆BFA, DE = BF (proved)
∠E = ∠F (each 90°)
DC = BA (given)
∆DEC = ∆BFA (by RHS)
and so ∠3 = ∠4 (by CPCT)
ar (OED) = ar (OFB) [∴ AOED = AOFB] …(1)
ar (DEC) = ar (BFB) [∴ ADEC = ABEA] …..(2)
Adding (1) and (2), we get
ar (OED) + ar (DEC) = ar (OFB) = ar (BFA)
ar (OCD) = ar (OAB) …..(3)

2. Adding ar (OBC) on both sides of equation (3)
ar (OCD) + (OBC) = ar (OAB) + ar (OBC)
ar (DCB) = ar (ACB)

3. ∆DCB and ∆ACB have the same base BC and have equal area
∴ they will lie between the same parallels BC and AD
and so BC ∥ AD
∠3 and ∠4 are A.I.A’s and are equal
∴ AB ∥ DC
In quadrilateral ABCD, AB ∥ DC and AB = DC (given)
ABCD is a parallelogram.

Question 7.
D and E are points on sides AB and AC respectively of ∆ABC such that ar (DBC) = ar (EBQ. Prove that DE ∥ BC.
Solution:
Given
ar (DBC) = ar (EBC)
To prove:
DE ∥ BC

Proof:
∆ DBC and ∆EBC have the same base BC and
ar (DBC) = ar (EBC)
∴ They will lie between the same parallel lines DE and BC.
and so DE ∥ BC

Question 8.
XY is a line parallel to side BC of a triangle ABC. If BE ∥ AC and CF ∥ AB meet XY at E and F respectively, show that ar (ABE) = ar (ACF).
Solution:
Given
XY ∥ BC, BE ∥ AC and CF ∥ AB.
To prove
ar (ABE) = ar (ACF)
Proof:
In quadrilateral ACBE, AE ∥ CB (∴ BC ∥ XY)
and AC ∥ EB
ACBE is a ∥^gm

Similarly ABCF is a parallelogram.
∥^gm ACBE and ABCF have the same base BC and are between the same parallels BC and AY.
∴ ar (ACBE) = ar (ABCF)
ar (ABE) + ar (ABC) = ar (ABC) + ar (ACF)
∴ ar (ABE) = ar (ACF)

Question 9.
The side AB of a parallelogram ABCD is produced to any point P. A line through A and parallel to CP meets CB produced at Q and then parallelogram PBQR is completed (see Fig. below). Show that ar (ABCD) = ar (PBQR).
[Hint: Joint AC and PQ. Now compare ar (ACQ) and ar (APQ).]

Solution:
Given
ABCD and BPRQ are parallelograms. CP ∥ AQ
To prove:
ar (ABCD) = ar (PBQR)
Construcion:
Join AC and PQ
Proof:
∆ACQ and ∆APQ lie on the same base AQ and are between the same parallels AQ and CP.
∴ ar (ACQ) = ar (APQ)
⇒ ar (ABQ) + ar (ABC) = ar (ABQ) + ar (BQP)
∴ ar (ABC) = ar (BQP) …..(i)

Multiplying (1) by 2 on both sides
2 ar (ABC) = 2 ar (BQP)
∴ ar (ABCD) = ar (PBQR)
[∴ ABCD and PBQR are parallelogram]

Question 10.
Diagonals AC and BD of a trapezium ABCD with AB ∥ DC intersect each other at C. Prove that ar (AOD) = ar (BOC).
Solution:
Given
ABCD is a trapezium in which AB ∥ DC.
To prove:
ar (AOD) = ar (BOC).

Proof:
∆ADC and ∆BCD lie on the same base DC and between the same parallels AB and CD.
∴ ar (ADC) = ar (BCD)
Subtracting ar (DOC) from both sides
ar (ADC) – ar (DOC) = ar (BCD) – ar (DOC)
ar (AOD) = ar (BOC)

Question 11.
In Fig. ABCDE is a pentagon. A line through B parallel to AC meets DC produced at F. Show that:

1. ar (ACB) = ar (ACF)
2. ar (AEDF) = ar (ABCDE).

Solution:
Given
ABCDE is a pentagon.
To prove:
1. ar (ACB) = ar (ACF)

2. ar (AEDF) = ar (ABCDE)
Proof:
∆ACB and ∆ACF lie on the same base AC and between the same parallels AC and BE.
ar (ACB) = ar (ACF)

3. Adding ar (AEDC) on both sides
ar (ACB) + ar (AEDC) = ar (ACF) + ar (AEDC)
ar (ABCDE) = ar (AEDF)

Question 12.
A villager Itwaari has a plot of land of the shape of a quadrilateral. The Gram Panchayat of the village decided to take over some portion of his plot from one of the corners to construct a Health Centre. Itwaari agrees to the above proposal with the condition that he should be given equal amount of land in lieu of his land adjoining his plot so as to form a triangular plot. Explain how this proposal will be implemented.
Solution:
Given.
ABCD is a quadrilateral.
Construction:
Join AC. Draw DE ∥ CA which intersect BA produced at E.

Proof:
∆ADC and ∆ACE both lie on the same base AC and between the same parallels AC and DE.
ar (ADC) = ar (ACE)
Adding ar (ABC) on both sides
ar (ADC) + ar (ABC) = ar (ACE) + ar (ABC)
ar (ABCD) = ar (EBC)

Question 13.
ABCD is a trapezium with AB ∥ DC. Aline parallel to AC intersects AB at X and BC at Y. Prove that ar (ADX) = ar (ACY).
[Hint: Join CX.]
Solution:
Given
ABCD is trapezium with AB ∥ DC and AC ∥ XY.
To prove:
ar (ADX) = ar (ACY).
Construction:
Join CX.
Proof:
∆ADX and ∆ACX both lie on the same base AX and between the same parallel AN and DC.

∴ ar (ADX) = ar (ACX) …(1)
∆ACX and ∆ACT both lie on the same base AC and between the same parallels AC and AT.
ar (ADY) = ar (ACX) …(2)
From (1) and (2), we get
ar (ADX) = ar(ACT)

Question 14.
In Fig. below AP ∥ BQ ∥ CR. Prove that ar (AQC) = ar (PBR).

Solution:
Given:
AP∥BQ∥CR.
To prove:
ar (AQC) = ar (PBR)
Proof:
∆ABQ and ∆PBQ both lie on the same base BQ and between the same parallels AP and BQ.
∴ ar (ABQ) = ar (PBQ) …(1)
∆BCQ and ∆BRQ both lie on the same base BQ and between the same parallels BQ and CR.

∴ ar (BCQ) = ar (BRQ) …(2)
Adding (1) and (2), we get
ar (ABQ) tar (BCQ) = ar (PBQ) + ar (BRQ)
∴ ar (AQC) = ar (PBR)

Question 15.
Diagonals AC and BD of a quadrilateral ABCD intersect at 0 in such a way that ar (AOD) = ar (BOC). Prove that ABCD is a trapezium.
Solution:
Given:
ar (AOD) = ar (BOC)
To prove:
ABCD is a trapezium.

Proof:
ar ∠AOD = ar (BOC) (given)
Adding ar (AOB) on both sides
ar (AOD) + ar (AOB) = ar (BOC) + ar (AOB)
ar (ABD) = ar (ABC)
∆ABD and ∆ABC both lie on same base AB and have equal area.
∴ they will lie between the same parallels.
⇒ AB ∥ DC
∴ ABCD is a trapezium.

Question 16.
In Fig. below, ar (DRC) = ar (DPC) and ar (BDP) = ar (ARC). Show that both the quadrilaterals ABCD and DCPR are trapeziums.

Solution:
Given
ar (DRC) = ar (DPC)
ar (BDP) = ar (ARC)
To prove:
ABCD and DCPR are trapezium.

Proof:
∆DRC and ∆DPC both lie on the same base DC and have equal area .•. They will lie between the same parallels.
⇒ DC ∥ BP
and so DCPR is a trapezium.
ar (BDP) = ar (ARC) [given] …(1)
ar (DPC) = ar (DRC) [given] …(2)
Subtracting (1) and (2), we get
ar (BDP) – ar (DPC) = ar (ARC) – (DRC)
ar (BDC) = ar (ADC)
∆ADC and ∆BDC both lie on same base DC and have equal area.
∴ they will lie between the same parallels
⇒ AB ∥ DC
and so ABCD is a trapezium.

MP Board Class 9th Maths Solutions

MP Board Class 7th Science Solutions Chapter 17 Forests: Our Lifeline

Forests: Our Lifeline Intex Questions

Question 1.
What would happen if forests disappear?
Answer:

1. If forests disappear, the amount of carbon dioxide in air will increase, resulting in the increase of earth’s temperature.
2. In the absence of trees and plants, the animals will not get food and shelter.
3. In the absence of trees, the soil will not hold water which will cause floods.
4. Deforestation will ending our life and environment. Think, what, we can do to preserve our forests.

Forests: Our Lifeline Text Book Exercises

Question 1.
Explain how animals dwelling in the forest help it grow and regenerate?
Answer:
Animals help in growing and regenerating forests in many ways. Animals help in dispersing, seeds of certain plants. The decaying animal dung also provides nutrients to the seedling to plant. By this number of plants are growing which serve as a food for a number of herbivorous animals.

Herbivorous helps the carnivores to grow as they serve as food for them. So, the flora and fauna grows in the forests. Also, the animals work as the cleaning agents in the forest micro – organisms work on the death bodies of plants and animals and regenerate them.

Question 2.
Explain how forest prevent floods?
Answer:
If trees or widely we can say that forests are not present, rain will directly hit the ground and may cause the flood the area around it. Also, the heavy rain may damage the soil. Roots of trees and grasses basically bind the soil together, but in the absence of soil, they will be washed away or eroded.

The washed soil will get deposited in river and thus reduce the water carrying capacity of rivers. Which is the major causes of flood. Also, forests can absorb a lot of water. This also helps in preventing floods.

Question 3.
What are decomposers? Name any two of them. What do they do in the forest?
Answer:
The micro – organisms which convert the dead plants and animals to humus are known as decomposers. These micro – organisms play an important role in the forest. The any two decomposers are grubs and beetles. They clean the forests of the decaying dead bodies and replenishes the nutrient back to the forest soil.

Question 4.
Explain the role of forest in maintaining the balance between oxygen and carbon – dioxide in the atmosphere?
Answer:
Plants release oxygen through the C0₂ photosynthesis. The Plants help to provide oxygen for animal respiration. They also maintain the balance of oxygen and carbon dioxide in the atmosphere. That is why forests are called lungs.

Question 5.
Explain why there is no waste in a forest?
Answer:
The decomposers decompose the dead organisms. The decomposed matter is absorbed by plants as nutrients. Thus, there is no waste in a forest.

Question 6.
List five products we get from forests?
Answer:
We get following products from forests:

1. Medicine
2. Spice
3. Wood
4. Honey.
5. Gum

Question 7.
Fill in the blanks:

1. The insects, butterflies, honeybees and birds help flowering plants in ………………………..
2. A forest is a purifier of ……………………………. and …………………………
3. Herbs form the ……………………………… layer in the forest.
4. The decaying leaves and animal droppings in a forest enrich the ………………………….

Answer:

1. Pollination
2. Water, air
3. Lowest
4. Humus.

Question 8.
Why should we worry about the conditions and issues related to forests far from us?
Answer:
We should be worried about deforestation, as it would lead to floods, increase in earth’s temperature, depriving animals of their habitats and soil erosion.

Question 9.
Explain why there is a need of variety of animals and plants in a forest?
Answer:
Variety of animals are necessary for their survival and maintenance of food chain. For example, grass is eaten by insects, which in turn, are eaten by the frog. The frog is consumed by snakes and snakes is eaten by eagles.

Thus, it forms a food chain. There are so many food chains in the forest. All of these are linked. If any one food chain is disturbed, it affects other food chains. Also, animals convert the death plants and animals into humus and increase the fertility of soil.

Question 10.
In figure, the artist has forgotten to put the labels and directions on the arrows. Mark the directions on the arrows and label the diagram using the following labels: clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil roots, water table?
Answer:

Question 11.
Which of the following is not a forest product?

1. Gum
2. Plywood
3. Sealing wax
4. Kerosene

Answer:
4. Kerosene.

Question 12.
Which of the following statements is not correct?

1. Forests protect the soil from erosion.
2. Plants and animals in a forest are not dependent on one another.
3. Forests influence the climate and water cycle.
4. Soil helps forests to grow and regenerate.

Answer:
2. Plants and animals in a forest are not dependent on one another.

Question 13.
Micro – organisms act upon the dead plants to produce?

1. Sand
2. Mushrooms
3. Humus
4. wood.

Answer:
3. humus.

Extended Learning – Activities and Projects

Question 1.
The Department of Environment is to decide whether some portion of a forest in your area could be cleared for a housing complex. Write a letter to the department explaining your point of view as a concerned citizen?
Answer:
Do yourself.

Question 2.
Visit a forest? Here is a list of points that would make your visit more fruitful?

1. Make sure that you have permission to go into the forest.
2. Make sure that you can find your way around. Get a map and go along with some one who is familiar with the area.
3. Keep a record of the things you see and do. Observations make the visit interesting. Sketches and photographs are useful.
4. You may record bird calls.
5. Collect different kinds of seeds or hard fruits like nuts.
6. Try to recognise various types of trees, shrubs, herbs, etc. Make lists of plants from different places in the forest and of different layers. You may not be able to name all the plants, but it is worth recording and seeing where they grow. Make a record of approximate heights of plants, crown shape, bark texture, leaf size, and flower colour.
7. Learn to recognise the animal’s droppings.
8. Interview the forest officials and the people of surrounding villages and other visitors.
9. You must never collect birds eggs, and their nests should never be disturbed.

Answer:
Do yourself.

Forests: Our Lifeline Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (a)
Plants give out during photosynthesis?
(a) carbon dioxide
(b) oxygen
(c) humus
(d) none of these.
Answer:
(b) oxygen

Question (b)
Interdependence of animals for food is called –
(a) food – order
(b) food – cycle
(c) food – chain
(d) none of these.
Answer:
(c) food – chain

Question (c)
Small trees and grass and shrubs from the –
Answer:
(a) Canopy
(b) Under stories
(c) Lowest canopy
(d) All of these
Answer:
(b) Under stories

Question (d)
Deforestation leads to
(a) Soil erosion
(b) Floods
(c) Both of these
(d) None of these
Answer:
(c) Both of these

Question 2.
Fill in the blanks:

1. The branch part of a tree above the stem is known as the ……………………… of the tree.
2. The micro – organisms which convert the dead plants and animals to humus are known as …………………………
3. The plants help to provide ………………………….. for animal respiration.
4. The plants maintain the balance of oxygen and carbon dioxide in the …………………………
5. The covered ground with decaying material acts like a ……………………………
6. The root system helps water to seep down in the ……………………………
7. Forests protect the soil from ………………………..
8. Forests are the lifeline for the forest dwelling …………………………….

Answer:

1. Crown
2. Decomposers
3. Oxygen
4. Atmosphere
5. Sponge
6. Ground
7. Erosion
8. Communities.

Question 3.
Which of the following statements are true (T) or false (F):

1. Forests cause rain on the earth.
2. In a forests, the herbs form the lowest layer of the vegetation.
3. The various components of the forest are not interdependent on one another.
4. The forests keeps on growing and changing, and can regenerate.
5. Soils helps forests to grow and regenerate.
6. Forests influence climate, water – cycle and air quality.
7. Forests is a renewable natural resources.

Answer:

1. True
2. Ture
3. False
4. True
5. True
6. True
7. True.

Forests: Our Lifeline Very Short Answer Type Questions

Question 1.
What do you mean by forest?
Answer:
Forest is a place hosting a number of animals and plants.

Question 2.
Name any two trees in forest?
Answer:
Sheesham, Neem.

Question 3.
Write any three things we get from forests?
Answer:
Gum, medicine and wood.

Question 4.
Which plants constitute canopy in forests?
Answer:
Tall and giant trees.

Question 5.
What is the basic unit of any food chain?
Answer:
Plants.

Question 6.
Write one food chain in forest?
Answer:
Grass → Insects → Frog → Snake → Eagle

Question 7.
How is forest environment?
Answer:
Forest environment is peaceful and a cool breeze is blowing.

Question 8.
Name some animals that live deep inside forest?
Answer:
Bison, Jackals, Boar, Elephants.

Question 9.
What is humus?
Answer:
Humus is a dark coloured substance which is formed from the dead bodies of plants and animals.

Question 10.
What happens if an animal dies in the forest?
Answer:
The dead animals become food for vultures, jackals, insects and crows.

Question 11.
How does forest help in preventing floods?
Answer:
Forests absorb the rain .water in the soil and prevent the floods.

Question 12.
What is seed dispersal?
Answer:
The method by which plants scatter their seeds to reduce competition between off springs.

Question 13.
Define soil erosion?
Answer:
The weaving away of the soil by wind or water.

Question 14.
What do you mean by canopy?
Answer:
The branches of the tall trees look like a roof over the other plants in the forest is called canopy.

Question 15.
Define crown?
Answer:
Branch part of a tree above the stem is known as the crown.

Question 16.
What is deforestation?
Answer:
Cutting and destroying the forest is called deforestation.

Question 17.
What are the effects of deforestation?
Answer:
Floods, rising temperature, scarcity of flood and wood and disturbed flood chains are the results of deforestation.

Question 18.
What do you mean by afforestation?
Answer:
Planting more trees is called afforestation.

Question 19.
What would happen if it rains heavily in your town?
Answer:
There will be water logging or even flood. Everything will be in a mesh. No food, no water. No place, no stay.

Forests: Our Lifeline Short Answer Type Questions

Question 1.
Define soil erosion?
Answer:
Removal of fertile top layers of earth (soil) is called soil erosion. The soil erosion can be brought about by various agents like – water, wind, glaciers and ocean waves. Erosion occurs in both wet and arid regions. The various human activities like falling of trees, over – cropping and improper tilling accelerate soil erosion. The soil erosion can lead to floods.

Question 2.
What are the major factors that lead to soil erosion? Name them?
Answer:
The major factors that lead to soil erosion are the following:

1. Overgrazing by livestock
2. Deforestation
3. Over cultivation
4. Poor irrigation facilities
5. Water logging
6. Shifting cultivation.

Question 3.
Write about the dependence of animals on plants?
Answer:
Dependence of Animals on Plants:

1. Plants produce food by the process of photosynthesis and animals depend directly or indirectly on them for food.
2. Plants produce oxygen during photosynthesis and animals use this oxygen for respiration.
3. Plants act as habitat for the animals dwelling on trees.

Question 4.
Write about the dependence of plants on animals?
Answer:
Dependence of Plants on Animals:

1. Animals produce carbon dioxide during respiration which is released in the atmosphere. Plants use this oxygen for preparing food.
2. A number of insects, birds and bats help in pollination.
3. Some animals help in dispersal of fruits and seeds.

Question 5.
How forests help in bringing rain?
Answer:
Trees absorbs water from the soil through their roots. They then release the excess of water through the process of transpiration in the form of water vapours. These water vapours form clouds and clouds bring rain.

Question 6.
How are forests useful to us?
Answer:
The forests are very useful to us for the following reasons:

1. They conserve soil and water.
2. They are helpful in causing rains.
3. They give us food and fruit.
4. They are the natural habitats of animals.
5. They help in the maintenance of ecological balance.

Question 7.
Write a short note on deforestation?
Answer:
Deforestation is another important cause which brings about soil erosion. Deforestation leads to depletion of water vapour in the atmosphere so which in turn adversely affects the formation of rain bearing clouds and consequently the rainfall. In the absence of adequate rainfall, the soil dries up and its nutrient value is affected.

The decrease in rainfall affects the growth of plants and trees, thus leads to the formation of deserts. When there is no plant cover over the earth, it becomes naked. When rain falls over this naked earth, the water does not percolate down the earth and washes away. Similarly, strong winds also take away the top soil, thus causing soil erosion.

Question 8.
In which layer of the soil would you find humus? What is its importance to the soil?
Answer:
Humus is found in the top of layer of soil. The presence of humus ensures that the nutrients of the dead plants and animals are released into the soil. From there, these nutrients are again absorbed by the roots of the living plants.

Forests: Our Lifeline Long Answer Type Questions

Question 1.
How we can conserved the forests?
Answer:

1. Unplanned and indiscriminate deforestation must be stopped.
2. Forest should not be over – exploited.
3. Use of wood as fuel should be discouraged.
4. Plant new fast growing trees.
5. Protect forest from fires, insects and diseases.
6. Protect national parks, wildlife sanctuaries or biosphere reserves.
7. Follow the guidelines of international organizations like W.W.F. and UNESCO for forest conservation.

Question 2.
Write the uses of forests?
Answer:
Forests are useful to us for the following reasons:

1. Forests provide timber for building and furniture.
2. Forests keep the environment cool and increase the chances of rainfall.
3. The roots of the trees hold the soil firmly thereby checking soil erosion.
4. Forests provide habitat to a variety of wild plants and animals.
5. The plants of forests use CO₂ and release oxygen in photosynthesis, thereby maintaining balance of gases in atmosphere.
6. Forests provide animal products such as honey, lac, wax, etc.
7. Forests provide plant products such as fruits, nuts, gums, resins, fibres, medicines, essential oil (like sandal wood), etc.
8. They are involved in the absorption of water which percolates in the soil, thereby becoming a part of the groundwater.

Question 3.
What will happen if forests disappear?
Answer:

1. Soil erosion will increase which will affect soil fertility and productivity.
2. Air pollution will increase which will ultimately threaten thirty existence of life on the Earth.
3. Unpredictable changes will take place in weather and climate.
4. Reduction in rainfall.
5. Reduction in recharging of existing water resources
6. Wildlife may also disappear along with forest.
7. Shortage of forest products.
8. Disturbance in ecological balance.
9. Increase in temperature
10. Global warming may reach in flooding of low lying area.

Question 4.
Draw a figure to show the difference between canopy and under stories?
Answer:

Question 5.
Draw a figure to show in the dependence of plant, soil and decomposers in a forest?
Answer:

MP Board Class 7th Science Solutions

MP Board Class 9th Science Solutions Chapter 12 Sound

Sound Intext Questions

Sound Intext Questions Page No. 162

Question 1.
How does the sound produced by a vibrating object in a medium reach your ear?
Answer:
When an object vibrates, it allows the particles of the medium around it to vibrate. It exerts force on the adjacent particles and continue oscillating in all directions and one of it, hit our ear’s medium which creates sound. This process continues in the medium till the sound reaches your ear.

Sound Intext Questions Page No. 163

Question 1.
Explain how sound is produced by your school bell.
Answer:
When the bell rings, it continues to move forward and backward which creates vibration and simultaneously a series of compressions and rarefactions which produce a very loud sound.

Question 2.
Why are sound waves called mechanical waves?
Answer:
Sound waves needs medium to propagate therefore, they are called mechanical waves. Sound cannot travel in the absence of a medium. Sound waves are propagated through a medium because of the interaction of the particles present in that medium.

Question 3.
Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
No, because sound waves needs a medium through which they can propagate. And since there is no medium on the moon due to absence of atmosphere, one cannot hear any sound produced by his / her friend on the moon.

Sound Intext Questions Page No. 166

Question 1.
Which wave property determines.

1. loudness
2. pitch?

Answer:

1. Amplitude determines loudness of a sound wave.
2. Frequency determines pitch of a sound wave.

Question 2.
Guess which sound has a higher pitch: guitar or car horn?
Answer:
Guitar has a higher pitch than car horn, because sound produced by the strings of guitar has higher frequency and since pitch is proportional to frequency, pitch of guitar will be higher.

Question 3.
What are wavelength, frequency, time period and amplitude of a sound wave?
Answer:

1. Wavelength: Wave length is the length between two consecutive peaks it is represented by Greek letter λ (lambda). Louder sound has shorter wavelength and softer sound has longer wavelength.
2. Frequency: The number of sound waves produced in unit time is called the frequency of sound waves. Frequency is measured in seconds. Frequency is denoted by Greek letter v (nu). The SI unit of frequency is ‘hertz’.
3. Amplitude: Amplitude of a wave is magnitude of maximum disturbance on either side of the normal position or mean value in a medium.

Question 4.
How are the wavelength and frequency of a sound wave related to its speed?
Answer:
Speed, wavelength, and frequency of a sound wave are related as follows:
Speed (ν) = Wavelength [λ] × Frequency (v)
⇒ ν = λ × v

Question 5.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Answer:
Given,
Frequency of the sound wave, v = 220 Hz
Speed of the sound wave, u = 440 ms^-1
Putting the equations,
Speed = Wavelength (λ) × Frequency (v)
ν = λ × v
∴ λ = \(\frac { ν }{ v  }\) = \(\frac { 440 }{ 220 }\) = 2 m
Hence, Wavelength = 2 m.

Question 6.
A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
Answer:
Given,
Frequency = 500 Hz
Distance = 450 m
Since, T = \(\frac { 1 }{ Frequency }\)
= \(\frac { 1 }{ 500 }\) = 0.002 sec.
Hence, person will listen the sound after every 0.002 sec.

Question 7.
Distinguish between loudness and intensity of sound.
Answer:
Intensity drives loudness of a sound. These both qualities of sound are proportional to each other. The amount of sound passing through a unit area per second represents intensity of a sound wave. While loudness is the response of the ear to the sound (amount received to pinna). The loudness of a sound is defined by its amplitude. The amplitude of a sound decides its intensity, which in turn is perceived by the ear as loudness.

Sound Intext Questions Page No. 167

Question 1.
In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
Answer:
Sound travels the fastest in solids medium (here Iron) then in liquids (water) and it is the slowest in gases (air). Therefore, for a given temperature, sound travels as follows (decreasing order): ⇒ Iron > water >air.

Sound Intext Questions Page No. 168

Question 1.
An echo returned in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms^-1?
Answer:
Given,
Speed, v = 342 ms^-1
Time, t = 3 s
Since, Distance = v × t
= 342 × 3 = 1026 m
Condition,
In fixed time interval, sound has to travel a distance that is twice the distance of the reflecting surface and the source.
Hence, the distance of the reflecting surface from the source = \(\frac { 1026 }{ 2 }\) m = 513 m.

Sound Intext Questions Page No. 169

Question 1.
Why are the ceilings of concert halls curved?
Answer:
Ceilings of concert halls are curved to:

1. Enhance loudness and echo of sound created.
2. Sound after reflection (from the walls) spreads uniformly in all directions.

Sound Intext Questions Page No. 170

Question 1.
What is the audible range of the average human ear?
Answer:
The audible range of an average human ear is between 20 Hz to 20,000 Hz.

Question 2.
What is the range of frequencies associated with

1. Infrasound?
2. Ultrasound?

Answer:

1. Infrasound: frequencies less than 20 Hz.
2. Ultrasound: frequencies more than 20,000 Hz.

Sound Intext Questions Page No. 172

Question 1.
A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?
Answer:
Given,
Time taken by the sonar pulse to return, t = 1.02s
Speed of sound in salt water, v = 1531 ms^-1
Distance of the cliff from the submarine = Speed of sound × Time taken
= 1531 × 1.02 m = 1561.62 m
Distance travelled by the sonar pulse during its transmission and reception in water
= 2 × Actual distance = 2d
Actual distance,
d = Distance of the cliff from the submarine / 2 = \(\frac { 1561 }{ 2 }\) = 780.31 m.

Sound NCERT Textbook Exercises

Question 1.
What is sound and how is it produced?
Answer:
Sound is a form of energy which is received at our ear pinna and gives the sensation of hearing. It is a vibration which propagates in air and developed by vibrating objects.

Question 2.
Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
Answer:
When vibration is produced by a body, it moves in backward and forward direction till the energy lasts. During forward movement it creates a region of high pressure. This region of high pressure is known as compressions. When it moves backward, it creates a region of low pressure. This region is known as a rarefaction. This is shown in figure given below.

Here,
C = compressions
R = rarefaction.

Question 3.
Cite an experiment to show that sound needs a material medium for its propagation.
Answer:
Arrange the instrument according to the picture given below:

• Take an electric bell and an air tight jar with glass bell and connect it to a vacuum pump.
• Suspend the bell inside the jar, and press the switch of the bell.

Method: Now pump out the air from the glass jar. The sound of the bell will become fainter and after some time, the sound will not be heard. This shows that sound needs a material medium to travel.

Question 4.
Why is sound wave called a ‘longitudinal wave’?
Answer:
Sound wave is called longitudinal wave because the air particles vibrates parallel to the direction of propagation of sound wave,it is produced by compressions and rarefactions in the air.

Question 5.
Which characteristics of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer:
The quality of pitch and loudness of sound enables us to identify our friend by his voice.

Question 6.
Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Answer:
Speed difference is the main reason of this happening. The speed of sound (344 m/s) is very less than the speed of light (3 × 10⁸ m/s). A flash is seen before we hear a thunder because sound of thunder takes more time to reach the Earth as compared to light.

Question 7.
A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 ms^-1.
Answer:
We know,
Speed (ν) = Wavelength × Frequency v
ν = λ × v
Given,
Speed of sound in air ν = 344 m/s (Given)

(i) For, v = 20 Hz
λ₁ = \(\frac { ν }{ v }\)
= \(\frac { 344 }{ 20 }\) = 17.2 m

(ii) For, v = 20000 Hz
12 = \(\frac { ν }{ v }\)
= \(\frac { 344 }{ 20000 }\) = 0.172 m
Hence, for humans, the wavelength range for hearing is 0. 0172 m to 17.2 m.

Question 8.
Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of time taken by the sound wave in air and in aluminium to reach the second child.
Answer:
Velocity of sound in air= 346 m/s
Velocity of sound waves in aluminium 6420 m/s
Let length of rod be 1.
Time taken for sound wave in air, t₁ = \(\frac { 1 }{ Velocity }\) in air.
Time taken for sound wave in aluminium, t₂ = \(\frac { 1 }{ Velocity }\) in aluminium.
Therefore,

= \(\frac { 6420 }{ 346 }\) = 18.55.

Question 9.
The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Answer:
Frequency =100 Hz. (Given)
This means the source of sound vibrates 100 times in one second.
Therefore, number of vibrations in 1 minute, i.e. in 60 seconds = 100 × 60 = 6000 times.

Question 10.
Does sound follow the same laws of reflection as light does? Explain.
Answer:
Yes, sound waves also follow the same laws of reflection as light wave do because:

1. Angle of incidence of sound is always equal to that of angle of reflection of sound waves.
2. The direction in which sound is incident, the direction in which it is reflected and normal all lie in the some plane.

Question 11.
When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of
sound production remains the same. Do you hear echo sound on a hotter day?
Answer:
An echo is heard when the time for the reflected sound is just 0.1 s
Time taken = \(\frac { Total Distance }{ Velocity }\)
On a hotter day, due to lighter medium the velocity of sound is more then a colder day. Hence, sound wave will move faster and if time taken by echo is less than 0.1 sec it will not be heard.

Question 12.
Give two practical applications of reflection of sound waves.
Answer:
Two practical applications of reflection of sound waves are:

1. Reflection of sound is used to measure the distance and speed of underwater objects. This method is known as SONAR.
2. Working of a stethoscope is also based on reflection of sound. In a stethoscope, the sound of the patient’s heartbeat reaches the doctor’s ear by multiple reflection of sound.

Question 13.
A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 10 ms^-2 and speed of sound = 340 ms^-1.
Answer:
Height of the tower, s = 500 m
Velocity of sound, v = 340 ms^-1
Acceleration due to gravity, g = 10 ms^-2
Initial velocity of the stone, u = 0 (since the stone is initially at rest)
Time taken by the stone to fall to the base of the tower t₁,
According to the second equation of motion:
s = ut₁ + \(\frac { 1 }{ 2 }\) gt₁²
500 = 0 × t₁ + \(\frac { 1 }{ 2 }\) × 10 t₁²
t₁² = 500
t₁ = 10 s
Now, time taken by the sound to reach the top from the base of the tower,  t₂ = \(\frac { 500 }{ 340 }\) = 1.47 s.
Therefore, the splash is heard at the top after time, t Where, t = t₁ + t₂ = 10 + 1.47 = 11.47 s.

Question 14.
A sound wave travels at a speed of 339 ms^-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Answer:
Speed of sound, v = 339 ms^-1
Wavelength of sound, λ = 1.5 cm = 0.015 m
Speed of sound = Wavelength × Frequency
ν = λ × v
∴ v = \(\frac { ν }{ λ }\)
= \(\frac { 339 }{ 0.015 }\)
= 22600 Hz.
The frequency range of audible sound for humans lies between 20 Hz to 20,000 Hz.
Since, the frequency of the given sound is more than 20,000 Hz, it is not audible.

Question 15.
What is reverberation? How can it be reduced?
Answer:
The repeated multiple reflections of sound in any big enclosed space is known as reverberation. The reverberation can be reduced by covering the ceiling and walls of the enclosed space with sound absorbing materials, such as fibre board, loose woollens, etc.

Question 16.
What is loudness of sound? What factors does it depend on?
Answer:
The effect produced in the brain by the sound of different frequencies is called loudness of sound. Loudness depends on the amplitude of vibrations. In fact, loudness is proportional to the square of the amplitude of vibrations.

Question 17.
Explain how bats use ultrasound to catch a prey.
Answer:
Bats produce high – pitched ultrasonic squeaks. These high – pitched squeaks are reflected by objects such as preys and returned to the bat’s ear. This allows a bat to know the distance of his prey.

Question 18.
How is ultrasound used for cleaning?
Answer:
Objects to be cleansed are put in a cleaning solution and ultrasonic sound waves are passed through that solution. The high frequency of these ultrasound waves detaches the dirt from the objects.

Question 19.
Explain the working and application of a SONAR.
Answer:
Sonar stands for Sound Navigation And Ranging. It is a device used to measure the depth, direction and speed of under – water objects such as submarines and ship wrecks with the help of ultrasounds and is also used to measure the depth of seas and oceans. An ultrasonic sound is produced and transmitted by the transducer (it is a device that produces ultrasonic sound) of the Sonar, which travels through sea water.

The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is converted into electrical signals. The distance (d) of the under – water object is calculated from the time (t) taken by the echo to return with speed (v) is given by 2d = v × t.

Question 20.
A SONAR device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.
Answer:
Given,
Time taken to hear the echo, t = 5 s
Distance of the object from the submarine, d = 3625 m
Total distance travelled by the sonar waves during the transmission and reception in water = 2d
Using formula:
Velocity of sound in water,
v = 2 \(\frac { d }{ t }\)
= 2 × \(\frac { 3625 }{ 5 }\) = 1450 ms^-1.

Question 21.
Explain how defects in a metal block can be detected using ultrasound.
Answer:
Defects in metal blocks do not allow ultrasound to pass through them and they are reflected back. This fact is used to detect defects in metal blocks. Ultrasound is passed through one end of a metal block and detectors are placed on the other end. The defective part of the metal block does not allow ultrasound to pass through it. As a result, it will not be detected by the detector. Hence, defects in metal blocks can be detected using ultrasound.

Question 22.
Explain how the human ear works.
Answer:
The human ear consists of three parts – the outer ear, middle ear and inner ear.

1. Outer ear: It is also termed ‘pinna’. It collects the sound from the surrounding and directs it towards auditory canal.
2. Middle ear: It is at the auditory canal where there is a thin membrane called eardrum or tympanic membrane. The sound waves set this membrane to vibrate. These vibrations are amplified by three small bones hammer, anvil and stirrup.
3. Inner ear: When vibration reach the cochlea in the inner ear and are converted into electrical signals which are sent to the brain by the auditory nerve, and the brain interprets them as sound.
   

Sound Additional Questions

Sound Multiple Choice Questions

Question 1.
Which of the following waves have no requirement of any medium to propagate?
(a) sound
(b) radio
(c) light waves
(d) none of above.
Answer:
(c) light waves

Question 2.
What kinds of waves are produced by sound?
(a) longitudinal only
(b) transverse waves only
(c) electromagnetic Waves
(d) both Longitudinal and Transversal.
Answer:
(a) longitudinal only

Question 3.
When a wave propagate, it transfers ___________ .
(a) energy only
(b) matter only
(c) both energy and matter
(d) none of these.
Answer:
(a) energy only

Question 4.
Note is a sound ___________ .
(a) of mixture of several frequencies
(b) of mixture of two frequencies only
(c) of a single frequency
(d) always unpleasant to listen.
Answer:
(a) of mixture of several frequencies

Question 5.
A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case:
(a) sound will be louder but pitch will not be different.
(b) sound will be louder and pitch will also be higher.
(c) sound will be louder but pitch will be lower.
(d) both loudness and pitch will remain unaffected.
Answer:
(d) both loudness and pitch will remain unaffected.

Question 6.
Earthquake produces which kind of sound before the main shock wave begins ___________ .
(a) ultrasound
(b) Infrasound
(c) audible sound
(d) none of the above.
Answer:
(b) Infrasound

Question 7.
Infrasound can be heard by ___________ .
(a) dog
(b) bat
(c) rhinoceros
(d) human beings.
Answer:
(c) rhinoceros

Question 8.
Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting ___________ .
(a) intensity of sound only.
(b) amplitude of sound only.
(c) frequency of the sitar string with the frequency of other musical instruments.
(d) loudness of sound.
Answer:
(c) frequency of the sitar string with the frequency of other musical instruments.

Question 9.
What we term to the number of oscillations completed in one second?
(a) time period
(b) velocity
(c) frequency
(d) wavelength.
Answer:
(c) frequency

Question 10.
Sound waves which can be propagate in solids are ___________ .
(a) Longitudinal only.
(b) Transverse only.
(c) Either longitudinal or transverse.
(d) Non mechanical waves only.
Answer:
(c) Either longitudinal or transverse.

Question 11.
In SONAR, we use ___________ .
(a) ultrasonic waves
(b) infrasonic waves
(c) radio waves.
(d) audible sound waves.
Answer:
(a) ultrasonic waves

Question 12.
Sound travels in air if ___________ .
(a) particles of medium travel from one place to another.
(b) there is no moisture in the atmosphere.
(c) disturbance moves.
(d) both particles as well as disturbance travel from one place to another.
Answer:
(c) disturbance moves.

Question 13.
When we change feeble sound to loud sound we increases ___________ .
(a) Frequency
(b) Amplitude
(c) Velocity
(d) Wavelength.
Answer:
(b) Amplitude

Question 14.
In the curve (Figure) half the wavelength is ___________ .
image
(a) AB
(b) BD
(c) DE
(d) AE
Answer:
(a) AB

Question 15.
The time taken to complete an osoillation ___________ .
(a) time period
(b) velocity
(c) frequency
(d) wavelength.
Answer:
(a) time period

Question 16.
The period of a vibrating body of frequency 100 Hz is ___________ .
(a) 100 seconds
(b) 10 seconds
(c) 0.1 second
(d) 0.01 second.
Answer:
(a) 100 seconds

Question 17.
Which of the following is SI unit of amplitude?
(a) metre
(b) s^-1
(c) metre / second
(d) Hertz.
Answer:
(a) metre

Question 18.
The quantity λ is known as ___________ .
(a) wave velocity
(b) frequency
(c) wavelength
(d) wave number.
Answer:
(c) wavelength

Question 19.
Sound wave of which of the following frequency is an ultrasonic sound?
(a) 30 Hz
(b) 300 Hz
(c) 3000 Hz
(d) 30,000 Hz.
Answer:
(d) 30,000 Hz.

Question 20.
In which of the following, speed of the sound is maximum?
(a) air
(b) water
(c) steel
(d) kerosene.
Answer:
(c) steel

Sound Very Short Answer Type Questions

Question 1.
How does sound travels in gases and liquids – as longitudinal or as transverse waves?
Answer:
As longitudinal waves.

Question 2.
Give examples of longitudinal waves.
Answer:
Sound waves.

Question 3.
What is speed of sound in air?
Answer:
At 0° C, it is 331 m/s. At 20°C, it is 341 m/s.

Question 4.
What is reverberation?
Answer:
The repeated reflection that results in the persistence of sound is called reverberation.

Question 5.
Among solids, liquids and gases sound travels faster in which medium?
Answer:
Sound travels the fastest in solids.

Question 6.
What is one Hz?
Answer:
Hz is the unit of frequency, called as Hertz. One Hertz is equal to one cycle per second.

Question 7.
What is ‘note’ of second?
Answer:
The sound produced due to a mixture of several frequency is called a note, it is pleasant to listen to.

Question 8.
What is pitch?
Answer:
The way our brain interprets the frequency of an emitted sound is called the pitch.

Sound Short Answer Type Questions

Question 1.
What is Sound? Why it is important for us?
Answer:
Sound is a longitudinal mechanical wave. Sound has great importance in our daily life. It gives us a sensation of hearing. It makes it possible to communicate with other persons through speech.

Question 2.
What is a mechanical wave?
Answer:
A mechanical wave is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion. The particles vibrating in turn do not move forward but the disturbance is carried forward.

Question 3.
What is a longitudinal wave?
Answer:
If the particles of a medium vibrate in a direction, parallel to or along the direction of propagation of wave, it is called longitudinal wave.

Question 4.
What type of waves can travel in vacuum? Give example(s).
Answer:
Electromagnetic waves can travel in vacuum. Sun light, x – rays are examples of electromagnetic waves.

Question 5.
Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?
Answer:
No, we will not hear any sound on the Moon. The Moon does not have any atmosphere, since sound is a mechanical wave and requires a medium to travel.

Question 6.
What are the factors, speed of sound wave depends upon?
Answer:
Speed of the sound depends on the following factors:

1. Inertial property of the medium (to store kinetic energy).
2. Elastic property of the medium (to store potential energy).
3. Temperature of the medium.
4. Density of the medium.
5. Humidity present in the medium (in air / gases).

Question 7.
Three persons A, B and C are made to hear a sound travelling through different mediums as given below:

Who will hear the sound first ? Why ?
Answer:
Person A will hear the sound first because sound travels the faster in solids than in liquids and gases.

Question 8.
If 20 waves are produced per second, what is the frequency in hertz?
Answer:
Number of waves per second is known as frequency.
∴ Frequency (v) = 20 Hz.

Question 9.
What is echo?
Answer:
The sound waves produced bounce back or gets reflected from the mountains or buildings and come to our ears, this reflected sound is known as Echo. To hear echo, the barrier reflecting the sound should be atleast at a distance of 17 metres.

Question 10.
What is infrasonic? Give an example.
Answer:
Sound having frequency less than 20 Hz is known as infrasonic sound or infrasonic. Waves produced during earthquake are infrasonic.

Sound Long Answer Type Questions

Question 1.
Establish the relationship between speed of sound, its wave length and frequency. If velocity of sound in air is 340 m s^-1, calculate:

1. wavelength when frequency is 256 Hz.
2. frequency when wavelength is 0.85 m.

Answer:
Derivation of formula ν = v λ

1. 340 = 256 λ ⇒ λ = 1.33 m.
2. 340 = v (0.85) ⇒ v = 400 Hz.

Question 2.
A girl is sitting in the middle of a park of dimension 12 m × 12 m. On the left side of it there is a building adjoining the park and on right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain answer.
Answer:
If the time gap between the original sound and reflected sound received by the listener is around 0.1 s, only then the echo can be heard. The minimum distance travelled by the reflected sound wave for the distinctly listening the echo, distance = velocity of sound × time interval;
= 344 × 0.1 = 34.4 m.
But, in this case the distance travelled by the sound reflected from the building and then reaching the girl will be (6 + 6 = 12 m),  which is much smaller than the required distance. Therefore, no echo can be heard.

Sound Higher Order Thinking Skills (HOTS)

Question 1.
A key of piano is struck gently and then struck again but much harder this time. What will happen in the second case?
Answer:
In second case, the loudness will increase as this will increase the amplitude of vibration of string. Pitch and frequency will also increase in force or tension in the string.

Question 2.
At a hill station, a child could hear the echo of his voice after 0.2 s. But, when he went to the same place in the afternoon, he could not hear echo at all. What could be the reason?
Answer:
In afternoon, the temperature rises, therefore the speed of sound also increased. The reflected sound will take very less time to travel back and no echo is heard.

Sound Value Based Question

Question 1.
It is not advisable to construct houses near airports, inspite of that many new residential apartments are constructed near airports. Rajesh / Sumit files RTI and also complains the municipal office about the same.

1. Why one should not reside near airport?
2. Name other two places where there is noise pollution.
3. What value of Rajesh is reflected in this act?

Answer:

1. The landing and taking off of the air – planes causes lot of noise-pollution which may lead to deafness, high blood pressure and other health problems.
2. The other two places where there is noise-pollution are residing near the heavy traffic routes and railway stations or lines.
3. Rajesh shows participating citizen and moral responsibility values.

MP Board Class 9th Science Solutions

MP Board Class 9th Maths Solutions Chapter 10 Circles Ex 10.3

Question 1.
Draw different pairs of circles. How many points does each pair have in common? What is the maximum number of common points?
Solution:
Let us draw different pairs of circles as shown below:

We gave,
In figure           Maximum number of common points
(i)             –                     nil
(ii)            –                    one
(iii)           –                    two
Thus, two circles can have at the most two points in common.

Question 2.
Suppose you are given a circle. Give a construction to find its center.
Solution:
Steps of construction:

1. Mark any three points A, B and C on the circle.
   
2. Join AB and BC.
3. Draw the perpendicular bisector of AS. Let it be PQ.
4. Draw the perpendicular bisector of BC. Let it be RS.
5. PQ and RS intersect at point O.
6. O is the center of given circle.

Question 3.
If two circles intersect at two points, prove that their centers lie on the perpendicular bisector of the common chord.
Solution:
Given:
Circles C(O, r) and C(D, r₁) intersect at A and B.
To prove:
OD is perpendicular bisector of AS.

Construction:
Join OA, AD, OB and BD.
Proof:
In ∆AOD and ∆BOD,
OA = OB
DA = DB (Radii of the circle)
OD = OD (Common)
∆AOD ≅ ∆BOD (By SXS)
and ∠1 = ∠2 (By CPCT)
In ∆OAC and ∆OBC,
OA = OB (Radii of the circle)
OC =OC (Common)
∠1 = ∠2 (Proved)
∆AOC = ∆OBC (By SAS)
So ∠3 = ∠4 (By CPCT)
and AC = BC (By CPCT)
∠3 + ∠4 = 180.°
2∠3 = 180°
∠3 = \(\frac{180^{\circ}}{2}\) =90° (UA’s)
OD is perpendicular bisector of AB.

MP Board Class 9th Maths Solutions

MP Board Class 7th Science Solutions Chapter 16 Water: A Precious Resource

Activities

Activity – 1
Given here is the rainfall map of India (Fig.) It gives the average annual rainfall in different regions of our country?

Question 1.
Are you blessed with sufficient rainfall?
Answer:
No.

Question 2.
Is there sufficient water available in your area throughout the year?
Answer:
Yes.

Question 3.
Can we attribute this to mismanagement of water resources?
Answer:
Yes.

Water: A Precious Resource Text Book Exercises

Question 1.
Mark T if the statement is true and F if it is false:

1. The freshwater stored in the ground is much more than that present in the rivers and lakes of the world.
2. Water shortage is a problem faced only by people living in rural areas.
3. Water from rivers is the only source for irrigation in the fields.
4. Rain is the ultimate source of water.

Answer:

1. True
2. False
3. False
4. True

Question 2.
Explain how groundwater is recharged?
Answer:
The ground water get recharged through the process of infiltration. The infiltration means seeping in water from rain, rivers and lakes into the empty spaces and crack deep below the ground.

Question 3.
There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?
Answer:
The effect on the water table depends on the replenishment of the underground water. As only five families will share a tubewell, the water used for daily domestic purpose will not effect the water table as such. But if there is acute shortage of rains the water used by the families will not replenished and water table will fall down.

Question 4.
You have been asked to maintain a garden. How will you minimise the use of water?
Answer:
By collecting rain water. Also to minimise the wastage of water we will use the new technique of drip irrigation, which directly throws water at the base of plants.

Question 5.
Explain the factors responsible for the depletion of water table?
Answer:
Increasing population:
Increasing population creates demand for construction of houses, shops, offices, roads and pavements. This decreases the open areas like parks, and playgrounds. This, in turn, decreases the seepage of rainwater into the ground. What could be the consequence? Recall that a pukka floor does not allow water to seep in easily, while in a grass lawn water seeps through in no time.

Moreover a huge amount of water is required for construction work. Often groundwater is used for this purpose. So, on the one hand we are consuming more groundwater, and on the other we are allowing lesser water to seep into the ground. This results in depletion of water table. In fact, the water table in some parts of many cities has gone down to alarmingly low levels.

Increasing industries:
Water is used by all the industries. Almost everything that we use needs water somewhere in its production process. The number of industries is increasing continuously. Water used by most of the industries is drawn from the ground.

Agricultural activities:
A majority of farmers in India depend upon rains for irrigating their crops. Irrigation systems such as canals are there only in a few places. Even these systems may suffer from lack of water due to erratic rainfall. Therefore, farmers have to use groundwater for irrigation. Population pressure on agriculture forces increasing use of groundwater day by day. This results in depletion of water table.

Question 6.
Fill in the blanks with the appropriate answers:

1. The water bearing layer of the earth is …………………………
2. The process of water seepage into the ground is called ………………………
3. The water bearing layer of the earth is ………………………
4. The process of water seepage into the ground is called ………………………….

Answer:

1. Well and handpumps
2. Solid (ice), liquid (water), gas (water vapour)
3. Aquifer
4. Infiltration.

Question 7.
Which one of the following is not responsible for water shortage?

1. Rapid growth of industries
2. Increasing population
3. Heavy rainfall
4. Mismanagement of water resources.

Answer:
3. Heavy rainfall.

Question 8.
Choose the correct option. The total water –

1. In the lakes and rivers of the world remains constant.
2. Under the ground remains constant.
3. In the seas and oceans of the world remains constant.
4. Of the world remains constant.

Answer:
3. In the seas and oceans of the world remains constant.

Question 9.
Make a sketch showing groundwater and water table? Lab T it?
Answer:

Extended Learning Activities and Projects

Question 1.
Role play?
You are a water detective in your school? You have a term of six members? Survey the campus and make a note of the following:

1. Total number of taps
2. Number of taps leaking
3. Amount of water wasted due to leakage
4. Reasons of leakage
5. Corrective measures taken.

Answer:
Do yourself.

Question 2.
Groundwater pumped out?
Try to find out if there are any hand pumps in your neighborhood. Go to the owner or the users of a few of these and find out the depth at which they struck water? If there are any differences/think of the probable reason? Write a brief report and discuss it in your class. If possible, visit a place water boring is going on to install a hand pump? Watch the process carefully and find out the depth of the water table at that place?
Answer:
Do yourself.

Question 3.
Catching rainwater – Traditional methods? Form groups of 4 to 5 students in the class and prepare a report on the various traditional ways of water harvesting. If possible, use the following web link: www.rainwaterharvesting.org.?
Answer:
Do yourself.

Question 4.
Conservation of water? Carry out a campaign to conserve water at home and in the school. Design posters to remind others of the importance of water resources?
Answer:
Do yourself.

Question 5.
Create a logo? Hold a competition to create a logo or a symbol depicting water scarcity?
Answer:
Do yourself.

Water: A Precious Resource Additional Important Questions

Objective Type Questions

Question 1.
Choose the correct alternative:

Question (a)
…………………………. is celebrated as the “world water day”?
(a) 22 March
(b) 20 March
(c) 22 April
(d) 20 April.
Answer:
(a) 22 March

Question (b)
Water is a Unique substance because?
(a) It is consumable
(b) It is colourless
(c) It exits in all three states
(d) Both (a) and (b)
Answer:
(c) It exits in all three states

Question (c)
Year …………………….. was observed as the International Year of fresh water to make people aware of this dwindling natural resource?
(a) 2002
(b) 2003
(c) 2004
(d) 2005.
Answer:
(b) 2003

Question (d)
The earth’s surface is covered with water about?
(a) 70%
(b) 71%
(c) 72%
(d) 73%.
Answer:
(b) 71%

Question (e)
Main source of water on earth is –
(a) rain
(b) snow
(c) glaciers
(d) all the above.
Answer:
(a) rain

Question (f)
One of these is not a source of surface water –
(a) lake
(b) rain
(c) river
(d) spring.
Answer:
(d) spring.

Question (g)
This is level …………………. of ground water?
(a) sea level
(b) rain
(c) aquifer
(d) (b) and (c).
Answer:
(d) (b) and (c).

Question (h)
Water has maximum density at –
(a) 0°C
(b) 4°C
(c) 98.4°C
(d) 100°C.
Answer:
(b) 4°C

Question (i)
Water is –
(a) a mixture
(b) a compound
(c) an element
(d) none of these.
Answer:
(b) a compound

Question (j)
The purest form of natural water is –
(a) river
(b) sea
(c) rain
(d) spring.
Answer:
(c) rain

Question (k)
Common salt content of sea water is –
(a) 1.5%
(b) 2.5%
(c) 3.5%
(d) 10%.
Answer:
(b) 2.5%

Question 2.
Fill in the blanks:

1. The amount of water recommended by the United Nations for drinking, cooking, washing and maintaining proper hygiene is a minimum of ……………………… liters per person per day.
2. The water that is fit for use is ………………………..
3. Solid form of …………………. water, and …………… , is present as ice caps at the poles of the earth.
4. ……………………. water is present in lakes, oceans, rivers and even underground.
5. The process of seeping of water into ground is called ………………………..
6. Water in the aquifiers can be usually pumped out with the help of …………………………. or ………………………..
7. Increase in population, industrial and agricultural activities are some common factors affecting ……………………….. table.
8. The rain water can be used to recharge the …………………………
9. Bhujpur in the Kutch area of ………………….. has a very erratic rainfall.
10. ……………………… irrigation is a technique of watering plants.

Answer:

1. 50
2. Fresh water
3. Snow, ice
4. Liquid
5. Infiltration
6. Tubewells, handpumps
7. Water
8. Groundwater
9. Gujarat
10. Drip.

Question 3.
Which of the following statements are true (T) or false(F):

1. Water is essential for all living beings.
2. Water exists in three forms.
3. There is an uneven distribution of water.
4. Water shortage has become a matter of concern throughout the world.
5. The gaseous form is the water vapour present in the air around us.
6. Many villages do not have water supply system.
7. The water – table does not varies from place to place.
8. Water drawn from under the ground gets replenished by seepage of rain water.
9. Rainwater harvesting is not necessary.
10. Rajasthan is a hot and dry place.
11. Water allows sunlight to pass through it.
12. Pure water has no taste.

Answer:

1. True
2. True
3. True
4. True
5. True
6. True
7. False
8. True
9. False
10. True
11. True
12. True.

Water: A Precious Resource Very short Answer Type Questions

Question 1.
What is the most important property of water?
Answer:
The most important property of water is its ability to dissolve various substances. Hence, it is called a universal solvent.

Question 2.
What are the sources of water?
Answer:
The two main sources of natural water are surface water and underground water or subsoil water.

Question 3.
What are the different states of water?
Answer:
The different states of water are solid, liquid and gas.

Question 4.
What are the characteristics of pure water?
Answer:
The pure water is colourless, odourless, tasteless and transparent.

Question 5.
What do you mean by a resource?
Answer:
Materials that we get from the environment to meet our needs are called resources.

Question 6.
A part from water, what are the other natural resources?
Answer:
A part from water, air, forests, minerals and fossilfuels are natural resources.

Question 7.
What is the percentage of water that is available for human beings?
Answer:
Only a tiny fraction about 0.01% of total water is used by human beings.

Question 8.
List the sources of water for your daily use?
Answer:
Sources of water for our daily use are well, lakes, rivers and ponds.

Question 9.
Define saturated solution?
Answer:
A saturated solution of a solute at a given temperature is a solution which contains as much of the solute as it can dissolve at that temperature.

Question 10.
Define unsaturated solution?
Answer:
If a solution contains less of the solute than what it can dissolve at that temperature, then it is called all unsituated  solution.

Question 11.
Name three forms of water?
Answer:
Three forms of water are solid, gaseous and liquid.

Question 12.
Which is universal solvent?
Answer:
Water.

Question 13.
What is the percentage of water (by weight) that an average elephant body has?
Answer:
An average elephant body has 80% water by weight.

Question 14.
If you have sample of tap water, well water and sea water, which do you think has the highest amount of salts?
Answer:
Sea water has highest amount of salts.

Question 15.
List the salts that can be obtained from the sea?
Answer:

1. Common salt (NaCl)
2. Sodium bromide (NaBr)
3. Potassium iodide (Kl)
4. Calcium salts.

Question 16.
Which sea has the highest salinity?
Answer:
Dead sea has the highest salinity.

Question 17.
Name two gaseous fuels which are prepared from water?
Answer:
Water gas and hydrogen gas.

Question 18.
Define water table?
Answer:
The depth at which water is found at a particular place is called water table.

Question 19.
What is Bawri?
Answer:
Bawri is a traditional way of collecting water.

Question 20.
What is potable water?
Answer:
The water which is fit for drinking is called potable water.

Question 21.
Define salinity of water?
Answer:
Water which has salts dissolved in it and is salty in taste is called salinity of water.

Question 22.
Define water cycle?
Answer:
The water from the earth reaches the atmosphere and from there it ultimately comes back to land, this is known as water cycle.

Question 23.
How does water cycle help in maintaining global climate?
Answer:
Liquid water on heating turns into water vapours. Water vapour on cooling again forms liquid water. This change of state of water over and over again makes the cycle in nature.

Question 24.
How are clouds formed?
Answer:
Water vapours being lighter and rise up in the atmosphere. At the upper layer of the atmosphere, where the temperature is lower. The vapours get condensed into tiny water droplets and clouds are formed.

Question 25.
Which unwanted material could be present in the water that you get from your local water supply?
Answer:
The unwanted materials in our water supply are dust particles, germs, bacteria and many other materials as impurities.

Question 26.
Define water harvesting?
Answer:
Most of the water that we get as rainfall just flows aways. This is a waste of precious natural resource. The rainwater can be used to recharge the groundwater. This is known as water harvesting or rainwater harvesting.

Question 27.
Define drip irrigation?
Answer:
Drip irrigation is a technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant.

Water: A Precious Resource Short Answer Type Questions

Question 1.
Wrote a short note on source of water?
Answer:
Water is available to us through various sources. Rain water, lake Water, river water, sea water are some of the sources. Natural water from all these sources contain some impurities these are the dissolved minerals and salts. Apart from that, they contain some insoluble impurities too.

Question 2.
List the sources of water on the earth?
Answer:
There are two main sources of natural water:

1. Underground water
2. Surface water.
3. Underground Water: There are mainly two types of underground water –
   • (a) Well water
   • (b) Spring water.

2. Surface water:
It is of three types:

• Rain water
• River and lake water
• Sea water.

Question 3.
Write a short rote an river water?
Answer:
The river water is mainly due to rain or due to melting of snow on the mountains. The river water usually carries some suspended impurities and some soluble impurities. The soluble impurities are the dissolved salts and minerals. Apart from that they may carry certain micro – organisms and organic matter due to contamination.

Question 4.
Write a short note on sea water?
Answer:
Sea water is the largest source of natural water. But it is not fit either for drinking or for irrigation directly. This is because it contains a large number of dissolved salts of chlorides, bromides, iodides, sulphates and carbonates. The sea water is a rich source for common salt. It is recovered from sea water by evaporation and then is purified to remove the other impurities present.

Question 5.
Write a short note an underground water?
Answer:
Water present underneath the earth is tapped as it is an excellent source of pure drinking water. We usually dig wells. Depending on the geographical conditions of the place, the depth in which water is available is estimated. Well water contains some dissolved impurities.

Again the nature of the impurities depends on the geographical conditions. We also get water from springs under the earth. Such springs usually contain some dissolved mineral salts. However the spring water does not contain suspended impurities as it comes from deep under the earth.

Question 6.
Write a short note on rain water?
Answer:
It is the purest form of natural water available to us. Though the first few droplets of rain bring along with them some dust particles and micro-organisms, the later drops are free from impurities.

Question 7.
What are the properties of water?
Answer:
Properties of Water:

1. Pure water is colourless, odourless and tasteless.
2. Pure water freezes at 0 degree Celsius and boils at 100 degree celsius.
3. The density of water is 1 g/cc. It means that 1 cc of water at 1 degree Celsius weighs 1 gram.

Question 8.
What are the different ways by which water vapour is put into the atmosphere?
Answer:
The different ways by which water vapours put into atmosphere are as follows:

1. Factories and thermal stations produce a lot of steam and put is into the atmosphere.
2. Water in ponds, rivers and lakes, ocean gets evaporated due to atmospheric heat.
3. Plants throughout water vapours during respiration.

Question 9.
What makes the sea water so saline?
Answer:
Rivers flowing from different places bring water containing dissolved salts and minerals into the sea. Sea water is continuously evaporated by the heat of the sun. This evaporated water forms clouds and again fall on the earth as rain. This rain water again dissolves salts into it and goes into the sea. Thus the amount of salts in sea water goes on increasing.

Question 10.
How will you show that saline water is not fit for agriculture?
Answer:
Take two healthy plants of same type. Water both the plants separately one with ffesh water and other with saline water. Continue to water similarly for seven days and observe. The plant which was watered with saline water wilts. This shows that saline water is not fit for plants or agriculture.

Water: A Precious Resource Long Answer Type Questions

Question 1.
Draw a diagram to show water cycle?
Answer:

Question 2.
What are the causes of water scarcity?
Answer:
Causes of Water Scarcity:

1. Overpopulation
2. Over – irrigation for agriculture
3. Water pollution
4. Climatic change and variability
5. Indiscriminate cutting of forest
6. Increase in demand for water
7. Misuse of water
8. Poor water resource management
9. Disputes between the states for sharing water
10. Destruction of natural water reservoirs.

Question 3.
What are the methods to prevent water scarcity? Ans. Methods to prevent water scarcity:

1. Control population by adopting small family norms
2. Prevent misuse and wastage of water
3. Prevent water pollution
4. Replace large flush tanks with smaller ones.
5. Build dams, bunds and tanks to store rainwater.
6. Replace large flush tanks with smaller ones.
7. Recharge underground water
8. Recycle waste water for gardening
9. Follow drip irrigation or low water sprinklers for agriculture.

Question 4.
What are the effect of water scarcity on the life of people?
Answer:
Effect of water scarcity on the life of the people:

1. Long walk to fetch water.
2. Have to pay high price for buying water.
3. Low scope for generating employment.
4. Uncertainty over availability of water for agriculture.
5. Area will remain backward and neglected.
6. Increase incidents of crime.
7. More incidence of diseases due to poor sanitary conditions.
8. Fall in the productivity of animals.

MP Board Class 7th Science Solutions