# The Solid State Class 12 Important Questions Long Answer Type With PDF

## The Solid State Class 12 Important Questions Long Answer Type With PDF

Question 1
(a) An element has an atomic mass 93 g mol-1 and density 11.5 g cm-3. If the edge length of its unit cell is 300 pm, identify the type of unit cell.
(b) Write any two differences between amorphous solids and crystalline solids.
(a) Given:
M = 93 g mol-1; ρ = 11.5 g cm-3;
a = 300 pm = 300 × 10-10 cm = 3 × 10-8 cm
Using formula,
Z = ρ×a3×NAM
= 11.5×(3×10−8)3×6.022×102393
= 2.01 (approx.)
As the number of atoms present in given unit cells are coming nearly equal to 2, hence the given units cell is body centered cubic unit cell (BCC).

Question 2
(a) Calculate the number of unit cells in 8.1 g of aluminium if it crystallizes in a f.c.c. structure. (Atomic mass of Al = 27 g mol-1)

(b) Give reasons:
(i) In stoichiometric defects, NaCl exhibits Schottky defect and not Frenkel defect.
(ii) Silicon on doping with Phosphorus form n-type semiconductor.
(iii) Ferrimagnetic substances show better magnetism than antiferromagnetic substances. (Delhi) 2017
(a) Given:
Mass of Al = 8.1,
Atomic mass of Al = 27 g mol-1
No. of atoms = η × 6.022 × 1023
= 8.127 × 6.022 × 1023
= 0.3 × 6.022 × 1023
= 1.8066 × 1023
Since one f.c.c. unit cell has 4 atoms
∴ No. of unit cells = 1.8066×10234
= 4.5 × 1022 unit cells
(b) (i) Schottky defect is shown by the ionic solids having very small difference in their cationic and anionic radius whereas Frenkel defect is shown by ionic solids having large difference in their cationic and anionic radius. NaCl exhibits Schottky defect because radius of both Na+ and Cl have very small difference.
(ii) Phosphorus is pentavalent that is it has 5 valence electrons, an extra electron results in the formation of n-type semi conductors on doping with Silicon. The conductivity is due to presence of extra electrons.
(iii) In antiferromagnetic substances the magnetic moments of domains are half aligned in one direction and remaining half in opposite direction in the presence of magnetic field so magnetic moment will be zero while in ferrimagnetic substances the magnetic moments of domains are aligned in parallel and anti-parallel directions in unequal numbers, hence shows some value of magnetic moment. ## The Solid State Class 12 Chapter 1 Chemistry Important Questions And Answers PDF

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Question 1.
Which point defect in crystals does not alter the density of the relevant solid?
Frenkel defect.

Question 2.
Which point defect in its crystal units alters the density of a solid?

Schottky defect.

Question 3.
Which point defect in its crystal units increases the density of a solid?
Metal excess defect increases the density of a solid. It is due to presence of extra cations in the interstitial sites.

Question 4.
How do metallic and ionic substances differ in conducting electricity?

The electrical conductivity in metallic substances is due to free electrons while in ionic substances the conductivity is due to presence of ions.

Question 5.
Which point defect of its crystals decreases the density of a solid?
Schottky defect.

Question 6.
What is the number of atoms in a unit cell of a face-centred cubic crystal?

The number of atoms in a unit cell of fcc-crysta! is 4 atoms.

Question 7.
Write a feature which will distinguish a metallic solid from an ionic solid.

The electrical conductivity in metallic solid is due to free electrons while in ionic solid the conductivity is due to presence of ions.

Question 8.
Which point defect in crystals of a solid does not change the density of the solid?

Frenkel defect.

Question 9.
Which point defect in crystals of a solid decreases the density of the solid?

Schottky defect.

Question 10.
What type of interactions hold the molecules together in a polar molecular solid?

Dipole-dipole forces of attractions hold the molecules together in a polar molecular solid.

Question 11.
What type of semiconductor is obtained when silicon is doped with arsenic?

n-type semiconductor.

Question 12.
Write a distinguishing feature of metallic solids.

Metallic solids possess high electrical and thermal conductivity due to presence of free electrons.

Question 13.
‘Crystalline solids are anisotropic in nature.’ What does this statement mean?

It means that crystalline solids show different values of their some properties like electrical conductivity, refractive index, thermal expansion etc. in different directions.

Question 14.
Which stoichiometric defect in crystals increases the density of a solid?

Interstitial defect in crystals increases the density of a solid.

Question 15.
What is meant by ‘doping’ in a semiconductor?

Addition of a suitable impurity to a semiconductor to increase its conductivity is called doping.

Question 16.
Write a point of distinction between a metallic solid and an ionic solid other than metallic lustre.
Metallic solid conducts electricity in solid state but ionic solids do so only in molten state or in solution or metals conduct electricity through electrons and ionic substances through ions. Metallic solids are malleable and ductile while ionic solids are hard and brittle.

Question 17.
How may the conductivity of an intrinsic semiconductor be increased?

The conductivity is increased by adding an appropriate amount of suitable impurity. This process is called as intrinsic doping.

Question 18.
Which stoichiometric defect increases the density of a solid?
Interstitial defect increases the density of a solid.

Question 19.
What are n-type semiconductors?

n-type semiconductor : They are obtained by doping silicon with an element of group15, like P, As etc.

Question 20.
What type of stoichmetric defect is shown by AgBr and Agl ?

AgBr shows both Frenkel defect and Schottky defect whereas Agl shows Frenkel defect.

Question 21.
What type of defect can arise when a solid is heated ?

Vacancy defects can arise when a solid is heated.

Question 22.
Why does LiCl acquire pink colour when heated in Li vapours?

This is due to metal excess defect due to anionic vacancies in which the anionic sites are occupied by unpaired electrons (F-centres).

Question 23.
How many atoms constitute one unit cell of a face-centered cubic crystal?

4 atoms constitute one unit cell of a fee crystal.

Question 24.
What type of stoichiometric defect is shown by AgCl?

Frenkel defect is shown by AgCl.

Question 25.
What type of substances would make better Permanent Magnets: Ferromagnetic or Ferrimagnetic?

Ferromagnetic substances would make better I permanent magnets
Example : Fe, Co, Ni etc.

Question 26.
Calculate the number of atoms in a face centred cubic unit cell.

In face centered cubic arrangement, number of lattice points are : 8 + 6.
∴ Lattice points per unit cell = 8×18+6×12 = 4

Question 27.
On heating a crystal of KC1 in potassium vapour, the crystal starts exhibiting a violet colour. What is this due to?

The Cl ions diffuse to the surface and combine j with atoms which get ionized by losing electrons. ! These electrons are trapped in anions vacancies j and act as F-centre which imparts violet colour to the crystal.

Question 28.
Which type of ionic substances show Schottky defect in solids?

Highly ionic compounds with high coordination rjuniber and small difference in size of cations and anions show schottky defect.

Question 29.
How many atoms per unit cell (z) are present in bcc unit cell?

Number of atoms in a unit cell of a body centred cubic structure :
Contribution by 8 atoms on the corners
= 18 × 8 = 1
Contribution by the atom presents within the body = 1
∴ Total number of atoms present in the unit cell = 1 + 1 = 2 atoms

Question 30.
What type of stoichiometric defect is shown by NaCl?

Schottky defect is shown by NaCl.

Question 31.
Write a distinguishing feature between a metallic solid and an ionic solid.

The electrical conductivity in metallic substances is due to free electrons while in ionic substances the conductivity is due to presence of ions.

Question 32.
Why are crystalline solids anisotropic?

Crystalline solids show different values of their some properties like electrical conductivity, refractive index, thermal expansion etc. in different directions.

Question 33.
What is meant by ‘antiferromagnetism’?

Antiferromagnetism : These substances possess zero net magnetic moment because of presence of equal number of electrons with opposite spins.

Question 34.
Write a distinguishing feature of a metallic solid compared to an ionic solid.

Metallic solid conducts electricity in solid state but ionic solids do so only in molten state or in solution or metals conduct electricity through electrons and ionic substances through ions. Metallic solids are malleable and ductile while ionic solids are hard and brittle.

Question 35.
What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 1/3rd of tetrahedral voids?

Formula is X2Y3.

Question 36.
What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 2/3rd of tetrahedral voids?

Y atoms are N (No. of tetrahedral voids are 2N), No. of tetrahedral voids occupied by X are
23 × 2N = 4N3
X : Y = 4N : 3N
Formula : X4Y3

Question 37.
What is the no. of atoms per unit cell (z) in a body-centred cubic structure?

Contribution by the atoms present at eight comers = 8 × 18 = 1
Contribution by the atoms present at centre = 1
Total number of atoms present in unit cell = 1 + 1 = 2

Question 38.
What type of stoichiometric defect is shown by AgCl?

AgCl shows Frenkel defect.

Question 39.
What type of magnetism is shown by a substance if magnetic moments of domains are arranged in same direction?

Ferromagnetism is shown by a substance if magnetic moments of domains are arranged in same direction. Question 40.
Give an example each of a molecular solid and an ionic solid.

Molecular solid → Iodine (I2)
Ionic solid → Sodium chloride (NaCl)

Question 41.
A metallic element crystallises into a lattice having a pattern of AB AB … and packing of spheres leaves out voids in the lattice. What type of structure is formed by this arrangement?

Tetrahedral void is formed in AB AB … pattern. The hexagonal close packing (hep) is formed in this arrangement.

Question 42.
A metallic element crystallises into a lattice having a ABC ABC … pattern and packing of spheres leaves out voids in the lattice. What type of structure is formed by this arrangement?

Octahedral voids are formed in ABC ABC … pattern. The cubic close packing (ccp) is formed in this arrangement.

Question 43.
What type of Stoichiometric defect is shown by AgCl?
Frenkel defect.

Question 44.
What type of stoichiometric defect is shown by NaCl?