The Solid State Class 12 Chemistry Important Questions

Important Questions Class 12

Please refer to The Solid State Class 12 Chemistry Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Chemistry based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Chemistry for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.

Class 12 Chemistry Important Questions The Solid State

Very Short Answer Questions

Question. Write a feature which will distinguish a metallic solid from an ionic solid.
Answer. (i) Metallic solids are malleable and ductile whereas ionic solids are hard and brittle. (ii) In solid state, ionic solids are electrical insulators because ions are not free to move about, e.g. NaCl, Na2SO4, etc. while metals are good electrical conductors in solid state because of the presence of free electrons e.g. copper, nickel etc.

Question. How many atoms per unit cell (Z) are present in bcc unit cell?
Answer. In a body centred cubic unit cell.

Question. What type of interactions holds the molecules together in a polar molecular solid? 
Answer. Strong dipole-dipole interactions

Question. 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?
Answer.

Question. What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 2/3rd of octahedral voids?
Answer. No. of Y atoms per unit cell in ccp lattice

[ ccp is same as face-centred cubic packing. us, no. of atoms = 4]
No. of octahedral voids = No. of atoms present in ccp lattice
No. of octahedral voids occupied by atoms

Question. Based on the nature of intermolecular forces, classify the following solids : Sodium sulphate, Hydrogen 
Answer : Sodium sulphate : Crystalline solid 
Hydrogen : Non-polar molecular solid.

Question. What happens when CdCl2 is doped with AgCl?
Answer : When CdCl2 is added to AgCl, a cationic vacancy defect is created i.e., an Ag+ ion from the lattice is absent from its position due to presence of adjacent Cd2+ ion.

Question. Give reason :
In stoichiometric defects, NaCl exhibits Schottky defect and not Frenkel defect. 
Answer : Since Schottky defect is shown by highly ionic compounds having small difference in the size of cations and anions, whereas Frenkel defect is shown by compounds having large difference in the size of cations and anions. Therefore, NaCl exhibits Schottky defect.

Question. AgCl shows Frenkel defect while NaCl does not. Give reason.
Answer : Frenkel defect is shown by those ionic substances which have large difference in the size of ions. Hence, AgCl shows frenkel defect but NaCl does not.

Question. What is meant by groups 12-16 compounds? Give an example.
Answer : Groups 12-16 compounds are formed by the combination of elements of group-12 and group-16. In groups 12-16 compounds, the bonds are not perfectly covalent and the ionic character depends upon the electronegativities of the two elements, e.g., ZnS. 

Question. Give reason :
Ferrimagnetic substances show better magnetism than antiferromagnetic substances. 
Answer : Ferrimagnetic substances have a net dipole moment due to unequal parallel and antiparallel 
alignment of magnetic moments whereas antiferromagnetic substances have net magnetic moment zero due to compensatory alignment of magnetic moments. Therefore, ferrimagnetic substances show better magnetism than antiferromagnetic substances. 

Question. Based on the nature of intermolecular forces, classify the following solids : Silicon carbide, Argon 
Answer : Silicon carbide : Covalent or network solid.
Argon : Non-polar molecular solid.

Question. Give reason :
Silicon on doping with phosphorus forms n-type semiconductor.
Answer : Since group 15 elements (e.g., phosphorus) have one electron excess to group 14 elements (e.g., silicon) after forming four covalent bonds. Thus, the extra free electron is responsible for the formation of n-type semiconductor.

Question. ZnO turns yellow on heating. Why?
Answer : Initially ZnO is white in colour at room temperature but on heating it loses oxygen which creates anion vacancy defect and it turns yellow.

The Solid State Class 12 Chemistry Important Questions

Question. What type of semiconductor is formed when Ge is doped with Al?
Answer : When germanium (Ge) is doped with aluminium (Al), p-type semiconductor is formed.

Question. Based on the nature of intermolecular force, classify the following solids : Benzene, Silver
Answer : Benzene : Non-polar molecular solid.
Silver : Metallic solid

Question. How will you distinguish between the following pair of terms :
Tetrahedral and octahedral voids?

Answer. A void surrounded by four atoms whose centre when joined forms tetrahedron is tetrahedral void. Number of tetrahedral voids = 2 × Number of atoms. A void surrounded by six atoms whose centre when joined forms an octahedron is called octahedral voids.
Number of octahedral voids = Number of atoms.

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

Question.  What type of point defect is produced when AgCl is doped with CdCl2?
Answer. Addition of CdCl2 to AgCl crystal causes impurity defect.
In this defect also one Cd2+ ion replaces two Ag+ ions from the crystal. One site is occupied by one Cd2+ ion and other site remains vacant.

Question. Account for the following : Schottky defects lower the density of related solids. 
Answer. Schottky defects occur when cations and anions are missing from their lattice site. Mass of unit cell decreases which decreases the density of the solid.

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

Question. What type of stoichiometric defect is shown by AgBr and AgI?
Answer. Frenkel defect is shown by ionic solids in which difference in size of cations and anions is large.
Examples : ZnS, AgI and AgBr.

Question. What type of defect can arise when a solid is heated?
Answer. On heating a solid vacancy defect is produced in the crystal. is is because on heating, some lattice sites become vacant.

Question. What are diamagnetic susbtances?
Answer. Substances which are weakly repelled by magnetic field are called diamagnetic and this property is called diamagnetism. Diamagnetism is shown by those substances in which all electrons are paired.
Examples : NaCl, H2O, C6H6, Zn2+

Question. Deffne the following term : Ferromagnetism
Answer. Ferromagnetism : Materials which are strongly attracted by magnetic field are called ferromagnetic materials and the property thus exhibited is caused ferromagnetism.
e.g., Fe, Co, Ni show ferromagnetism at room temperature.

Question. Why is Frenkel defects not found in pure alkali metal halides?
Answer. Frenkel defects is not found in alkali metal halides because the ions cannot get into the interstitial sites due to their larger size.

Question. What type of semiconductor is formed when silicon is doped with As?
Answer. n-type semiconductor is formed when silicon is doped with arsenic.

Question. What type of semiconductor is obtained when silicon is doped with boron?
Answer. p-type semiconductor is obtained when silicon is doped with boron

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

Question. What type of substances would make better magnets, ferromagnetic or ferrimagnetic?
Answer. Ferromagnetic substances because these substances become a permanent magnet.

Question. What type of magnetism is shown in the following alignment of magnetic moments?
Answer. Ferromagnetism

Question. Write the type of magnetism observed when the magnetic moments are oppositely aligned and cancel out each other.
Answer. Antiferromagnetism

Question. An ionic compound AB2 possesses CaF2 type crystal structure. Write the coordination number of A2+ and B– ions in crystals AB2.
Answer. Coordination number of A2+ = 8
Coordination number of B– = 4

Question. Write a distinguishing feature of metallic solids.
Answer. Malleable, ductile, lustrous and conductor of heat and electricity.

Question. Account for the following : Conductivity of silicon increases on doping it with phosphorus.
Answer. Silicon when doped with phosphorus, which contains five valence electrons, they occupy some of the lattice sites in silicon crystal. Four out of five electrons are used in the formation of four covalent bonds with the four neighboring silicon atoms. The fifth electron is extra and becomes delocalised. These delocalised electrons increases the conductivity of doped silicon.

Question. Explain the following with suitable examples : Piezoelectric effect
Answer. Piezoelectric effect : When the electricity is produced by applying mechanical stress on some polar crystals, it is known as piezoelectric effect. Quartz shows this property.

Question. “Stability of a crystal is related to the magnitude of its melting point.” How?
Answer. The crystalline solids have sharp melting points. Melting point of a solid is related to the force of attraction between its molecules. Higher the melting point of a crystalline substance, greater is the force between the constituent particles and hence, greater is the stability.

Question. Deffne primitive unit cells.
Answer. A unit cell in which constituent particles (lattice points) are present only at the corner positions is called primitive or simple unit cell.

Short Answer Questions

Question. Aluminium crystallises in a fcc structure. Atomic radius of the metal is 125 pm. What is the length of the side of the unit cell of the metal? 
Answer. For fcc (or ccp), a = 2 2r = 2 × 1.414 × 125 pm = 354 pm

Question. Calculate the packing efficiency of a metal for a simple cubic lattice. 
Answer. Packing efficiency

Question. The unit cell of an element of atomic mass 108 u and density 10.5 g cm–3 is a cube with edge length, 409 pm. Find the type of unit cell of the crystal. [Given : Avogadro’s constant = 6.023 × 1023 mol–1]
Answer. Atomic mass, M = 108 u, d = 10.5 g/cm3, a = 409 pm

Question. An element X crystallises in fcc structure. 208 g of it has 4.2832 × 1024 atoms. Calculate the edge of the unit cell, if density of X is 7.2 g cm–3.
Answer. For fcc structure Z = 4, d = 7.2 g/cm3
Let a be the edge length in pm

Question. Chromium metal crystallises in a body centred cubic lattice. The length of the unit cell edge is found to be 287 pm. Calculate the atomic radius of chromium.
Answer.

Question. The edge of the face-centred cubic unit cell of aluminium is 404 pm. Calculate the radius of aluminium atom.
Answer. Edge of the face-centred cubic unit cell,
a = 404 pm

Question. Account for following : (i) Zinc oxide on heating becomes yellow. (ii) Frenkel defect does not change the density of AgCl crystals.
Answer. (i) Zinc oxide is white in colour at room temperature. On heating, it loses oxygen and turns yellow.

Now, there is excess of zinc in the crystal and excess Zn2+ ions move to interstitial sites and the electrons to neighbouring interstitial sites.
(ii) Due to Frenkel defect, no ions are missing from the crystal as a whole. thus, there is no change in density.

Question. A copper crystal has a face-centred cubic lattice structure. Atomic radius of the copper atom is 128 pm. Calculate the density of copper. Atomic mass of copper = 63.5
Answer. For fcc, Z = 4

Question. Write any two differences between amorphous solids and crystalline solids. 
Answer : Differences between crystalline and amorphous solids are as follows :

The Solid State Class 12 Chemistry Important Questions

Question. An element has 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. 
Answer : 

The Solid State Class 12 Chemistry Important Questions

Question. Calculate the number of unit cells in 8.1 g of aluminium if it crystallizes in a fcc structure. (Atomic mass of Al = 27 g mol–1)
Answer : As 27 g of Al will contain 6.023 × 1023 atoms
∴ 8.1 g Al will contain
= 6.023 × 1023/27 × 8.1 atoms
= 1.8069 × 1023 atoms
In fcc, 4 atoms are present in one unit cell
∴ 1.8069 × 1023 atoms will be present in
1.8069 × 1023/4 = 4.517 × 1022 unit cells.

Question. Examine the given defective crystal.

Answer the following questions : (i) What type of stoichiometric defect is shown by the crystal? (ii) How is the density of the crystal affected by this defect? (iii) What type of ionic substances show such defect?
Answer. (i) Schottky defect
(ii) Density of the crystal decreases.
(iii) is defect is shown by ionic substances in which the cation and anion are of almost similar sizes.

Question. What are point defects? Describe two types of point defects.
Answer. Point defects are the irregularities or deviations from ideal arrangement around a point or an atom in a crystalline solid. Types of point defects are :
Stoichiometric defects : These are the point defects that do not disturb the stoichiometry of the solid.
They are also called intrinsic or thermodynamic defects.
In non-ionic solids :
(i) Vacancy defect : Some of the lattice sites are vacant, decreases the density of the substance.
(ii) Interstitial defect : Some constituent particles (atoms or molecules) occupy an interstitial site, increases the density of the substance. In ionic solids :
(i) Frenkel defect or dislocation defect : The smaller ion (usually cation) is dislocated from its normal site to an interstitial site. It does not change the density of the solid and is shown by ionic substances in which there is a large difference in the size of ions, e.g., ZnS, AgCl, AgBr and AgI due to small size of Zn2+ and Ag+ ions.
(ii) Schottky defect : Equal number of cations and anions are missing. It decreases the density of the substance and is shown by ionic substances in which the cation and anion are of almost similar sizes e.g., NaCl, KCl, CsCl and AgBr. AgBr shows both, Frenkel as well as Schottky defects.
Non-stoichiometric defects : When the ratio of the cations to the anions becomes different from that indicated by the ideal chemical formula, the defects are called non-stoichiometric defects.
Metal excess defect : (i) Due to anionic vacancies e.g., on heating crystals of NaCl in presence of Na vapour, some anions (Cl) leave lattice sites which are occupied by electrons called F-centres giving colour to crystals.
(ii) Due to presence of extra cations at interstitial sites e.g., on heating, white ZnO turns yellow as it loses oxygen and Zn2+ ions and the electrons occupy interstitial sites.
Metal deficiency defect : There are many solids which are difficult to prepare in the stoichiometric composition and less amount the metal as compared to the stoichiometric proportion

Question. Explain the following terms with suitable examples :
(a) Crystal defects
(b) Metal deffciency defects 

Answer. (a) Point defects are the irregularities or deviations from ideal arrangement around a point or an atom in a crystalline substance, whereas the line defects are the irregularities or deviations from ideal arrangement in entire rows of lattice points. These irregularities are called crystal defects.
(b) This type of defects generally occurs when metal shows variable valency. The defect arises due to the missing of cation from its lattice site and the presence of the cation having higher charge in the adjacent lattice site, e.g., FexO.

Question. An element with density 11.2 g cm–3 forms a fcc lattice with edge length of 4 × 10–8 cm. Calculate the atomic mass of the element. (Given : NA = 6.022 × 1023 mol–1)
Answer. Given : d = 11.2 g cm–3, Z = 4, a = 4 × 10–8 cm,
M = ?, NA = 6.022 × 1023 mol–1

Long Answer Questions

Question. The radius of Na+ ion is 95 pm and that of Cl ion is 181 pm. Predict whether the coordination number of Na+ ion is 6 or 4.
Answer. Radius of Na+ = 95 pm
Radius of Cl = 181 pm

The radius ratio lies between 0.414 – 0.732.
Hence, Na+ ions prefer to occupy octahedral holes having coordination number 6.

Question. In a face centred lattice of X and Y, X atoms are present at the corners while Y atoms are at face centres.
(a) What is the formula of the compound?
(b) What would be the formula of the compound if
(i) one of the X atom is missing from a corner in each unit cell.
(ii) two atoms of X are missing from the corners.
(iii) one atom of X from a corner is replaced by Z atom (also monovalent)?
Answer. 

Question. Silver crystallises with face-centred cubic unit cell. Each side of this unit cell has a length of 409 pm. What is the radius of silver atom?
Assume the atoms just touch each other on the diagonal across the face of the unit cell.
Answer. As the atoms just touch each other on the diagonal across the face of unit cell, therefore
b2 = a2 + a2 = 2a2
b = √2a                                                                      …(i)
Also b = r + 2r + r = 4r                                             …(ii)
From (i) and (ii), we get

Question. An element crystallises in a fcc lattice with cell edge of 250 pm. Calculate the density if 300 g of this element contains 2 × 1024 atoms.
Answer. Molar mass of element (M)

Question. The density of copper is 8.95 g cm–3. It has a face centred cubic structure. What is the radius of copper atom? (Atomic mass Cu = 63.5 g mol–1, NA = 6.02 × 1023 mol–1)
Answer. Let us assume Z = 4 (copper has fcc)

Question. Iron has a body centred cubic unit cell with a cell dimension of 286.65 pm. The density of iron is 7.87 g cm–3. Use this information to calculate Avogadro’s number.
(Gram atomic mass of Fe = 56 g mol–1).
Answer. Given : For bcc, Z = 2
a = 286.65 pm = 2.87 × 10–8 cm
d = 7.874 g cm–3, NA = ?

Question. The density of copper metal is 8.95 g cm–3.
If the radius of copper atom be 127.8 pm, is the copper unit cell simple cubic, body-centred cubic or face-centred cubic?
(Given : atomic mass of Cu = 63.54 g mol–1 and NA = 6.02 × 1023 mol–1
Answer. Given : d = 8.95 g cm–3, r = 127.8 pm,
M = 63.54 g mol–1
NA = 6.02 × 1023 mo1–1

Question. Silver crystallises in fcc lattice. If the edge length of the unit cell is 4.077 × 10–8 cm and density of the crystal is 10.5 g cm–3, calculate the atomic mass of silver. (NA = 6.02 × 1023 atoms mol–1)
Answer. Given, edge length a = 4.077 × 10–8 cm
density d = 10.5 g cm–3
For fcc lattice Z = 4, Atomic mass M = ?

Question. What are point defects? Describe two types of point defects.
Answer. Point defects are the irregularities or deviations from ideal arrangement around a point or an atom in a crystalline solid. Types of point defects are :
Stoichiometric defects : These are the point defects that do not disturb the stoichiometry of the solid.
They are also called intrinsic or thermodynamic defects.
In non-ionic solids :
(i) Vacancy defect : Some of the lattice sites are vacant, decreases the density of the substance.
(ii) Interstitial defect : Some constituent particles (atoms or molecules) occupy an interstitial site, increases the density of the substance. In ionic solids :
(i) Frenkel defect or dislocation defect : The smaller ion (usually cation) is dislocated from its normal site to an interstitial site.
It does not change the density of the solid and is shown by ionic substances in which there is a large difference in the size of ions, e.g., ZnS, AgCl, AgBr and AgI due to small size of Zn2+ and Ag+ ions.
(ii) Schottky defect : Equal number of cations and anions are missing. It decreases the density of the substance and is shown by ionic substances in which the cation and anion are of almost similar sizes e.g., NaCl, KCl, CsCl and AgBr. AgBr shows both, Frenkel as well as Schottky defects.
Non-stoichiometric defects : When the ratio of the cations to the anions becomes different from that indicated by the ideal chemical formula, the defects are called non-stoichiometric defects.
Metal excess defect :
(i) Due to anionic vacancies e.g., on heating crystals of NaCl in presence of Na vapour, some anions (Cl–) leave lattice sites which are occupied by electrons called F-centres giving colour to crystals.
(ii) Due to presence of extra cations at interstitial sites e.g., on heating, white ZnO turns yellow as it loses oxygen and Zn2+ ions and the electrons occupy interstitial sites.
Metal defiiency defect : There are many solids which are difficult to prepare in the stoichiometric composition and less amount the metal as compared to the stoichiometric proportion (any two).

The Solid State Class 12 Chemistry Important Questions