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The Solid State - Important Questions Model Paper In 12th Chemistry

Published on: 27/07/2018

The chapter The Solid State contains important questions in CBSE 12th Standard chemistry. It also covered with most important questions in The Solid State.
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Std: 12th Standard CBSE - Chemistry

chapter: - Model Question paper

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Questions:

1 Marks

7 x 1 = 7

What is meant by point defect in crystals?

Arrange the following according to their packing fractions:
Simple cubic, face-centred cubic, body-centred cubic.

Classify the following substances into ionic, covalent, molecular or metallic:
MgO, SO₂,I₂,H₂O (ice), SiO₂ (quartz), brass.

What type of crystalline solid is graphite?

Give an example of an ionic compound which shows Frenkel defect.

What is meant by an 'intrinsic semiconductor'?

Write a point of distinction between a metallic solid and an ionic solid other than metallic lustre.

Generic 2

3 x 2 = 6

Explain each of the following with a suitable example:
(i) Paramagnetiwsm
(ii) Frenkel defect in crystals.

Calculate the packing efficiency in case of a metal crystal for simple cubic lattice.

10.

A group 14 element is to be converted into n-type semiconductor by doping it with suitable impurity. To which group should this impurity belong?

Multiple Choice Question

10 x 1 = 10

11.

A compound M_pX_qhas cubic close packing(ccp) arrangement of X.Its unit cell structure is shown below.The empirical formula of the compound is

(a)

(b)

MX₂

(c)

M₂X

(d)

M₅X₁₄

12.

The fraction of the total volume occupied by the atoms present in a simple cube is

(a)

\(\pi\over4\)

(b)

\(\pi\over6\)

(c)

\(\pi\over3\sqrt{2}\)

(d)

\(\pi\over4\sqrt{2}\)

13.

Which of the following FCC structure contains cations in alternate tetrahedral voids ?

(a)

NaCl

(b)

ZnS

(c)

Na₂O

(d)

CaF₂

14.

In crystal structure of NaCl, total number of Cl^- ions in a unit cell is

(a)

(b)

(c)

(d)

15.

Which is not the correct statement for ionic solids in which positive and negative ions are held by strong electrostatic attractive forces ?

(a)

The radius ratio r^₊/r^- increases as coordination number increases

(b)

As the difference in size of ions increases, coordination number increases

(c)

When coordination number is eight, r⁺/r^- ratio lies between 0.225 to 0.414

(d)

In ionic solid of the type AX (ZnS, Wurtzite), the coordination number of Zn²⁺ and S^2- respectively are 4 and 4.

16.

The number of octahedral sites per sphere in fcc structure is

(a)

(b)

(c)

(d)

17.

An example of a face centered cubic lattice is

(a)

Zinc

(b)

Sodium

(c)

Copper

(d)

Caesium chloride

18.

In a tetragonal crystal

(a)

\(a=b=c,\alpha =\beta ={ 90 }^{ ° }\neq \gamma \)

(b)

\(\alpha =\beta =\gamma ={ 90 }^{ ° },a=b\neq c\)

(c)

\(\alpha =\beta =\gamma ={ 90 }^{ ° },a\neq b\neq c\)

(d)

\(\alpha =\beta ={ 90 }^{ ° }\gamma ={ 120 }^{ ° },a=b\neq c\)

19.

Wax is an example of

(a)

ionic crystal

(b)

covalent crystal

(c)

molecular crystal

(d)

amorphous crystal

20.

The property of crystalline solid is not

(a)

anisotropic

(b)

isotropic

(c)

hard

(d)

dense

Generic 5

2 x 5 = 10

21.

Compounds having general molecular formula \(AFe_{ 2 }O_{ 4 }\) are called ferrites and posses spinel type structures. Some common examples are \(MgFe_{ 2 }O_{ 4 }\) and \(ZnFe_{ 2 }O_{ 4 }\) They may be thought of being formed by replacing \(Fe^{ 2+ }\) ions present in \(Fe_{ 3 }O_{ 4 }\) by bivalent cations such as \(Mg^{ 2+ },Zn^{ 2+ }\) ions etc. Now answer the following questions :
(i) What types of materials are ferrites?
(ii) What are the main uses of ferrites?

22.

Certain crystals, when subjected to a mechanical stress get deformed and produce electricity due to displacement of ions. The electricity thus produced is called piezoelectricity and such crystals are called piezoelectric crystals. On the other hand, when such crystals are subjected to an electric field, the atomic displacements are produced which cause mechanical distortion in the crystals. These unique properties of piezoelectric crystals find several applications. Now, answer the following questions:
(i) How do piezoelectric crystals behave?
(ii) Mention one application of piezoelectric crystals.
(iii) Just like certain crystals piezoelectric crystals perform better even under mechanical stress and show' various application, how do you behave under stress? What values we can adopt from even these non-living crystals?

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Answers Key:

1 Marks

7 x 1 = 7

()
The defect caused by missing or displacement of atoms or ions in a crystal is called point defect.

()
Simple (0.52)

()
MgO=Ionic, SO₂=Polar molecular, I₂=non-polar molecular, H₂O=Hydrogen bonded molecular, SiO₂=Covalent or network, brass=metallic.

()
Graphite is covalent crystalline solid.

()
AgCl shows Frenkel defect.

()
Those semiconductors which are used in pure form are called 'intrinsic semiconductors'.

()
Metallic solids can conduct electricity due to movement of electrons in solid state, whereas ionic solids conduct electricity in molten state or in aqueous solution by movement of ions.

Generic 2

3 x 2 = 6

(i) Those substances which are attracted by a magnet and have unpaired electrons are called paramagnetic substances and the phenomenon is called paramagnetism, e.g. Ni, Co, and Cr are paramagnetic.
(ii) When in an ionic solid, the cation is, occupying void instead of its normal site, it leads to Frenkel defect. e.g. in AgCl, Ag+ occupies void,

Suppose the edge length of the unit cell = a and radius of the sphere = r Since the spheres are touching each other, a = 2r Now, there are eight spheres at the corners of the cube: Each sphere at the corner is shared by eight unit cells and the contribution per unit cell is 1/8 so that number of spheres per unit cell is 8 x 1/8 = 1 Volume of cube = a³ = (2r)³ = 8r³. Since simple cubic unit cell has only one atom per unit cells the volume of space occupied is \(\frac { 4 }{ 3 } \pi { r }^{ 3 }\)

\(Packing \ efficiency=\frac { Volume \ of \ one \ sphere }{ Volume \ of \ cubic \ unit \ cell } \times 100\)
\(\\ \frac { \frac { 4 }{ 3 } \pi { r }^{ 3 } }{ 8{ r }^{ 3 } } \times 100\)
= 52.37 or 52.4

10.

When a group 14 element having four valence electrons is doped with a group 15 element having 5 valence electrons, n-type semiconductor is formed, e.g. silicon is doped with phosphorus of group 15, four electrons of phosphorus out of five; make covalent bonds with four electrons of silicon leaving one electron free; which increases the electrical conductivity of silicon.

Multiple Choice Question

10 x 1 = 10

11.

MX₂

12.

\(\)

13.

(b)
ZnS

14.

(b)
4

15.

16.

(d)
1

17.

18.

(b)
\(\alpha =\beta =\gamma ={ 90 }^{ ° },a=b\neq c\)

19.

20.

(b)
isotropic

Generic 5

2 x 5 = 10

21.

(i) Ferrites are magnetic material.
(ii) They are used in telephones and memory loops in computers.

22.

(i) Piezoelectric crystals behaves as mechanical electrical transducer.
(ii) Piezoelectric crystals are used as pickups in record players where they produce electric signals by application of pressure.
(iii) We generally become tense and pessimistic under stress. But we should face every situation, accept every worst situation as challenge and maintain our mental balance. It will definitely result in our performance just like in piezoelectric crystals. We can learn from these non-living crystals to be optimistic as worst situations can be converted into an opportunity.