The Solid State Class 12 Chemistry Chapter 1

Very Important Questions for CBSE Class 12 Chemistry Chapter 1 – The Solid State

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01.Class 12 Chemistry Important Questions
02Very Important Questions for Class 12 Chemistry
03Important Questions for Class 12 Chemistry Chapter 1 The Solid State
04Solid State Class 12 Important Questions and Answers
05Chemistry Solid State Class 12 Important Questions and Answers PDF
06Solid State Class 12 Important Questions With Answers PDF
07Solid State Questions And Answers PDF
08Solid State Questions for Class 12 Chemistry
09Solid State Class 12 Important Questions With Answers
10Top Solid State Chemistry Questions and Answers PDF

SOLID STATE

  1. In the cubic arrangement the radius ratio is found to be 0.884. The structure of the crystal will be
    Ans. Body centered cubic
  2. Radius ratio of NaCl crystal is 0.532. The structure of the crystal is
    Ans. Octahedral

3.Number of particles present per unit cell of HCP crystal is
Ans. Six

  1. Iodine is an example of type of solid.
    Ans. Molecular
  2. The point defect which decreases the density of a solid is called as
    Ans. schottky defect
  3. Give an example of hcp and bcc crystal.
    Ans. hcp ZnS, ZnOP
    bcc = CsCI, CsBr
  4. Find the number of atoms per unit cell in a face centered cubic structure having only single atoms at its lattice point.
    Ans. For Fcc unit cell, no of atoms per unit cell
    = 8(corners)x 1/8+6(faces)x 1/2= 1 +3 =4
  5. Name the point defect responsible for colour in alkali metal halides.
    Ans. The defect is called as metal excess defect. Due to this F-centres are created which is responsible for colour in alkali metal halides.
  6. Name the element with which Germanium may be doped to produce n-type semi-conductor
    Ans. Arsenic (Gr-15)
  7. When Indium is added to Germanium which type of semiconductor is formed ?
    Ans. Indium (Gr-13) when added to Germanium (Gr-14) then p-type of semiconductor is formed.
  8. Write the Bragg’s equation
    Ans. nμ = 2d sin ∅
    where n = order of diffraction
    A= wave length of monochromatic light
    d= distance between two parallel planes containing constituent
    ∅= angle of diffraction
  9. Write two characteristies of ionic solid
    Ans. These are water soluble, possess high mp and bp, usually hard and brittle.
  10. In molecular solid the constituent particles are held together by.
    Ans. vander Waal’s force of attraction.
  11. Carborandum is a__type of solid while dry ice is a ___type of solid.
    Ans. Covalent, molecular.
  12. Which type of crystalline solids are good conductor of electricity ?
    Ans. Metallic crystals
  13. In a simple cubic crystal packing efficiency is
    Ans. 52.4%
  14. In which type of cubic crystal arrangement packing efficiency is maximum ?
    Ans. Face centered cubic crystal (74%)
  15. Which type of crystal defect decreases density of a crystal ?
    Ans. Schottky defect.
  16. If there are “N tetrahedral voids, then number of octahedral voids is
    Ans. N/2
  17. Octahedral void is created by lattice points
    Ans. Six
  18. Number of atoms in FCC crystal is
    Ans. 1+3 =4 atoms
  19. Which type of crystal defect increases the density of a solid 2
    Ans. interstitial defect.
  20. do metallic solid and ionic solid differ in conducting property ?
    Ans. Metallic solids conduct electricity due to movement of electrons and conductivity decreases with increase in temperature. lionic solids conduct electricity due to movement of ions only in fused state or in aqueous solution. The conductivity increases with increase in
    temperature.
  21. Which type of erystal defect does not change the density of solid ?
    Ans. Frenkel defect.
  22. What type of semiconductor is formed when silicon is doped with arsenic ?
    Ans. n-type semiconductor
  23. What is F-centres ?
    Ans. It is a centre where the electron is entrapped in the anion vacances. This type of crystal defect is also
    known as metal excess defect.
  24. What type of semiconductor is formed when silicon is doped with Gallium ?
    Ans.p-type semiconductor
  25. Write one application of semiconductor.
    Ans. Semiconductors are used in transistors to detect and amplify radio signals. There are also used in photovoltaic cell to convert light energy to electrical energy.
  26. Name the type of structure possessed by unit cell of CsCl.
    Ans. Body centered cubic (bcc) structure.
  27. How does electrical conductivity vary with temperature for semiconductors
    Ans. The electrical conductivity increases with increase in temperature for semiconductors due to increase in kinetic energy of electrons.
  28. What type of crystal defects are shown by ZnS.
    Ans. Frankel defect is shown by ZnS as the cationic SIze is less than the anionic size.
  29. What type of crystal defects are shown by AgBr?
    Ans. AgBr shows both Frenkel and Schottky defects.
  30. How many Chloride ions are there around Sodium ion in sodium chloride crystal
    Ans. Six

34.How will you distinguish between tetrahedral void and octahedral void 2
Ans. Tetrahedral void is surrounded by four spheres which lie at the vertices of a regular tetrahedron.Octahedral void is surrounded by six spheres, which lie at the vertices of a regular octahedron.

  1. What is co-ordination number?
    Ans. Co-ordination number is the number of nearest neighbours with which an atom is in contact. e.g. In a body centred cubic structure the co-ordination number is 8.
  2. Write the equation by which you can find atomic mass of a metal from its density and dimensions of unit cell.
    Ans. M =Pa³Na/Z
    where p = density
    a edge length of unit cell
    z number of atoms in unit cell
    NÀ =Avogadro’s number
  3. An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of the faces of the cube. What is the empirical formula of the compound?
    Ans. Number of A ions per unit cell=x8 (corners) = 1 Number of B ions per unit cell =X6 (faces) = 3
    So the empirical formula of the compound is AB, .
  4. What is n-type semiconductor
    Ans. When a silicon crystal is doped with atoms of
    Gr 15 elements (P, As, etc) then four valency electrons
    of each impurity atom form cOvalent bonds with silicon
    atoms. Since there is a free electron which is used for
    conduction, so it is called as n-type semiconductor.
  5. Gold crystalises in a fcc structure, what is the
    edge length of the unít cell ? Given radius of gold
    atom is 0.144 nm

    Ans. For Fcc unit cell, r= √2a/4
    a = 4r/√2=2√2r
    = 2×1.414×0.144
    =0.4973nm
  6. What type of forces operate in molecular solids?
    Ans. vander Waal’s force, dipole dipole interaction
    or hydrogen bonds may operate between the molecules
    of molecular solid.
  7. Write two characteristic properties of molecular
    solid.

    Ans. These are generally soft and have low density. These are bad conductor of heat and electricity
  8. Write two characteristic properties of ionic solid.
    Ans. These are soluble in water These are hard and brittle
    These are good conductor of electricity in molten state or aqueous solution.
  9. What type of solids are electrical conductor and malleable ?
    Ans. Metallic solids
  10. What type of solids are very hard and electrical insulator in solid state as well as in moten state?
    Ans. Covalent solids
  11. What do you mean by packing efficiency ? In which type of crystal arrangements packing efficiency is more ?
    Ans. The percentage of total space filled by the particle in a crystal is called as packing efficiency. The packing efficiency is more in a face centred cubic structure (74%).
  12. Khat type of stoichiometric defect is shown by ZnS?
    Ans. Frankel defect.
  13. What type of stoichiometric defect is shown by AgBr ?
    Ans. Frankel defect as well as Schottky defect.
  14. What is meant by point defect in crystals ?
    Ans. The defects in crystals arises due to the irregularity in arrangement of atoms or ions are called as point defects
  15. If ‘a’ is the edge length of the unit cell of a fcc crystal, then what is the distance of closest approach between the two atoms in the crystal 2
    Ans. In a fec crystal 4r = √2a
    2r= a/√2 or d= a/√2
    where d= distance of closest approach between two atoms.
  16. An a bcc crystal what is the relationship between
    atomic radius (r) and edge length (a) ?
    Ans. r=a(√3/4)
  17. What is the packing efficiency in a bcc arrangement of crystals ?
    Ans. 68%

Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions

Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions

The Solid State Class 12 Important Questions Very Short Answer Type

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

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

Answer:
Schottky defect.

Question 3.
Which point defect in its crystal units increases the density of a solid?
Answer:
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?

Answer:
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?
Answer:
Schottky defect.

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

Answer:
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.

Answer:
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?

Answer:
Frenkel defect.

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

Answer:
Schottky defect.

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

Answer:
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?

Answer:
n-type semiconductor.

Question 12.
Write a distinguishing feature of metallic solids.

Answer:
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?

Answer:
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?

Answer:
Interstitial defect in crystals increases the density of a solid.

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

Answer:
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.
Answer:
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?

Answer:
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?
Answer:
Interstitial defect increases the density of a solid.

Question 19.
What are n-type semiconductors?

Answer:
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 ?

Answer:
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 ?

Answer:
Vacancy defects can arise when a solid is heated.

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

Answer:
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?

Answer:
4 atoms constitute one unit cell of a fee crystal.

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

Answer:
Frenkel defect is shown by AgCl.

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

Answer:
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.

Answer:
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?

Answer:
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?

Answer:
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?

Answer:
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?

Answer:
Schottky defect is shown by NaCl.

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

Answer:
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?

Answer:
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’?

Answer:
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.

Answer:
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?

Answer:
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?

Answer:
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?

Answer:
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?

Answer:
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?

Answer:
Ferromagnetism is shown by a substance if magnetic moments of domains are arranged in same direction.

Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions 1

Question 40.
Give an example each of a molecular solid and an ionic solid.

Answer:
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?

Answer:
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?

Answer:
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?
Answer:
Frenkel defect.

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

Answer:
Schottky defect is shown by NaCl.

Question 45.
Which ionic compound shows both Frenkel and Schottky defects?

Answer:
Silver bromide (AgBr) shows both Schottky and Frenkel defect.

The Solid State Class 12 Important Questions Short Answer Type – I (SA – 1)

Question 46.
Explain how you can determine the atomic mass of an unknown metal if you know its mass density and the dimensions of unit cell of its crystal.

Answer:
Suppose edge of the unit cell = a pm
Number of atoms present per unit cell = Z
∴ Volume of unit cell = (a pm)3
= (a × 10-10cm)3 = a3 × 10-30 cm3
Density of unit cell =  Mass of unit cell  Volume of unit cell  ……………… (i)
Mass of unit cell = Number of atoms in the unit cell × mass of each atom
= Z × m
Mass of each atom =  Atomic mass  Avogadro’s no. =MN0
Substituting these values in equation (i), we get
Density of unit cell = Z×Ma3×10−30×N0
If a is in cm, d = Z×Ma3×N0 g/cm3
∴ Molar mass can be calculated as
M = d×a3×N0Z

Question 47.
Calculate the packing efficiency of a metal crystal for a simple cubic lattice.

Answer:
Percentage efficiency of packing of simple cubic lattice = 52.4%.

Question 48.
Define the following terms in relation to crystalline solids :
(i) Unit cell (ii) Coordination number Give one example in each case. (All India) 2011
Answer:
(i) Unit cell : The smallest three dimensional portion of a complete space lattice which when repeated over and again in different directions produces the complete space lattice is called the unit cell.
Example: Cubic unit cell, Hexagonal unit cell etc.
(ii) Coordination number : The number of nearest spheres with which a particular sphere is in contact is called co-ordination number.
Example : Co-ordination number of hexagonal (hep) structures is 12.

Question 49.
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:
Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions 2
So it forms cubic- closed packed (ccp) lattice or fee structure.

Question 50.
Explain the following terms with suitable examples : Ferromagnetism and Ferrimagnetism

Answer:
Ferromagnetic solids : The solids which are strongly attracted by external magnetic field and do not lose their magnetism when the external field is removed are called ferromagnetic solids. The property, thus exhibited, is termed as ferromagnetism.
Example: Fe, Co and Ni show ferromagnetism at room temperature.

Ferrimagnetic solids : The solids which are expected to show large magnetism due to the presence of unpaired electrons but in fact have small net magnetic moment, are called ferrimagnetic solids.
Example : Fe3O4 and ferrites.

Question 51.
An element X crystallizes in f.c.c 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:
Z = 4(fcc) A = 7,2 g/cm3 a = ?
4.2832 × 1024 atoms have mass = 208 g
6.022 × 1023 atoms have mass
= 2084.2832×1024 × 6.022 × 1023 = 29.24 (at. mass)
a3 = Z×Md×NA=4×29.247.2×6.022×1023
= 269.6 x 10-24 cm3
∴ a = 6.46 x 10-8 cm = 6.46 Å

Question 52.
What is a semiconductor? Describe the two main types of semiconductors.

Answer:
Semiconductor : The solid materials whose electrical conductivity lies between those of the typical metallic conductors and insulators are termed as semiconductors. The semiconductors possess conductivity in the range of 102 to 10-9 ohm-1 cm-1.
These are of two types :
(a) n-type semiconductors : Doping of higher group element impurity forms n-type semiconductors, e.g. when ‘As’ is doped in ‘Ge’.
(b) p-type semiconductors : Impurity of lower groups forms electron deficient bond in the structure. Electron deficiency develops to p-hole.

Question 53.
Account for the following:
(i) Schottky defects lower the density of related solids.
(ii) Conductivity of silicon increases on doping it with phosphorus.

Answer:
(i) Schottky defect produced due to missing of equal number of cation and anion from lattice as a result of which the density of the lattice solid decreases.
(ii) The conductivity of silicon increases due to negatively charged extra electron of doped pentavalent phosphorus.

Question 54.
Aluminium crystallizes in an fee 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 fee, Formula : r = a22√
Given: r = 125 pm
∴ a = 22–√r ÷ a = 22–√ × 125
⇒ a = 2 × 1.414 × 125 = 353.5 pm

Question 55.
(a) Why does presence of excess of lithium makes LiCl crystals pink?

(b) A solid with cubic crystal 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? (All India) 2013
Answer:
(a) This is due to metal excess defect due to anionic vacancies in which the anionic sites are occupied by unpaired electrons (F-centres).
(b) As atoms of Q are present at the 8 centres of the cube, therefore, number of atoms of Q in the unit cell = 18 × 8 = 1
The atom P is at the body centre .-. Number of atoms = 1
Ratio of atoms P : Q = 1 : 1
Hence, the formula of the compound is PQ.

Question 56.
(a) What change occurs when AgCl is doped with CdCl2?

(b) What type of semiconductor is produced when silicon is doped with boron? (All India) 2013
Answer:
(a) Impurity defect of ionic solids is produced when AgCl is doped with CdCl2. Due to this defect vacancies are created that result in higher electrical conductivity of the solid.
(b) p-type semi-conductor is obtained when silicon is doped with boron.

Question 57.
If NaCl is doped with 10-3 mole percent SrCl2, what will be the concentration of cation vacancies? (NA = 6.02 × 1023 mol-1)
Answer:
10-3 mol percent means 100 moles of NaCl are doped with 10-3 moles of SrCl2
∴ 1 mole of NaCl is doped with SrCl2
= 10−3100 = 10-5 mole
Since each Sr2+ ion introduces one cation vacancy
∴ Concentration of cation vacancies
= 10-5 mol/mol of NaCl
= 10-5 × 6.02 × 1023 mol-1
= 6.02 × 1018 mol-1

Question 58.
What is a semiconductor? Describe the tivo main types of semiconductors and contrast their conduction mechanism.
Answer:
Semiconductor : The solids which have intermediate conductivities between metals and non-metals i,e. between 10-6 to 104 π-1 m-31 are called semiconductors.
Example : Germanium and Silicon.
Main types of semiconductors are of two types :
(i) Intrinsic semiconductor : These are insulators at room temperature and become semiconductors when temperature is raised
(ii) Extrinsic semiconductor :
p-type semiconductor
n-type semiconductor
These are formed by dropping impurity of lower or higher group.
These are subdivided into two types :
• p-type semiconductor : When a silicon crystal is doped with atoms of group-13 elements like B, Al, Ga etc., the atom forms only 3 covalent bonds with the Si atom and 4th missing electron creates a hole which conducts electricity.
• n-type semiconductor : When a silicon crystal is doped with atoms of group-15 elements like P, As etc., then only four of the five valence electrons of each impurity atom, participate in 4 covalent bond formation and 5th e conducts electricity.

Question 59.
A compound forms hep structure. What is the total number of voids in 0.5 mol of it? How many of these are tetrahedral voids?

Answer:
No. of atoms in the hep = 0.5 × 6.022 × 1023
= 3.011 × 1023
No. of octahedral voids
= No. of atoms in packing = 3.011 × 1023
No. of tetrahedral voids
= 2 × No. of atoms in packing
= 2 × 3.011 × 1023 = 6.022 × 1023
∴ Total no. of voids
= 3.011 × 1023 + 6.022 × 1023 = 9.033 × 1023

Question 60.
An element crystallizes in a structure having fee unit cell of an edge 200 pm. Calculate the density if 200 g of this element contains 24 × 1023 atoms.

Answer:
24 × 1023 atoms of an element have mass = 200 g
∴ 6.022 × 1023 atoms of an element have mass
= 20024×1023 × 6.022 × 1023 = 50.18 g
Given : a = 200 pm = 200 × 10-12 cm,
Z = 4 (For fee), M = 50.18 g
Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions 3

Question 61.
An element with density 11.2 g cm-3 forms a f.c.c. 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 : p = 11.2 g cm-3, a = 4 × 10-8 cm
For fee lattice, Z = 4
Using formula,
Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions 4

Question 62.
Examine the given defective crystal 2014

Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions 5
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?
(tii) What type of ionic substances show such defect? (Delhi)
Answer:
(i) Schottky defect
(ii) Density of the crystal decreases
(iii) NaCl (Ionic solids having approximate equal size of cations and anions)

Question 63.
An element with density 2.8 g cm-3 forms a f.c.c. unit cell with edge length 4 × 10-8 cm. Calculate the molar mass of the element.
(Given : NA = 6.022 × 1023mol-1) (All India) 2014
Answer:
Important Questions for Class 12 Chemistry Chapter 1 The Solid State Class 12 Important Questions 6

Question 64.
(i) What type of non-stoichiometric point defect is responsible for the pink colour of LiCl?
(ii) What type of stoichiometric defect is shown by NaCl?

Answer:
(i) This is due to metal excess defect due to anionic vacancies in which the anionic sites are occupied by unpaired electrons (F-centres).
(ii) Schottky defect is shown by NaCl.

Question 65.
How will you distinguish between the following pairs of terms :
(i) Tetrahedral and octahedral voids
(ii) Crystal lattice and unit cell.

Answer:

Tetrahedral voidsOctahedral voids
1.It is much smaller than the size of spheres in  the packing.Size is much larger than tetrahedral voids.
2.Each tetrahedral void is surrounded by 4 spheres. Hence, co­ordination no. is 4.Each octahedral void is surrounded by 6 spheres. Hence, its co­ordination no. is 6.

(ii) A regular arrangement of the constituent particles of a crystal in a three dimensional space is called crystal lattice.
The smallest three dimensional portion of a complete crystal lattice, which when repeated over and again in different directions produces the complete crystal lattice is called the unit cell.

Question 66.
(i) Write the type of magnetism observed when the magnetic moments are appositively aligned and cancel out each other.
(ii) Which stoichiometric defect does not change » the density of the crystal?
Answer:

  1. Diamagnetism is observed when the magnetic moments are oppositively aligned and cancel out each other.
  2. Frenkel defect does not change the density of the crystal.

Question 67.
(i) Write the type of magnetism observed when the magnetic moments are aligned in parallel and anti-parallel directions in unequal numbers.
(ii) Which stoichiometric defect decreases the density of the crystal?

Answer:

  1. Ferrimagnetism is observed.
  2. Schottky defect decreases the density of the crystal.

68. Define the following terms:
(i) n-type semiconductor
(ii) Ferrimagnetism
Answer:
(i) n-type semiconductor : When Si/Ge is doped with group 15 element.
(ii) Ferrimagnetism : When magnetic domains are aligned in parallel and anti-parallel directions in unequal numbers.

Question 69.
Explain the following terms with suitable examples :
(i) Frenkel defect (ii) F-centres

Answer:
(i) Frenkel defect : The defect in which the smaller ion/cation is dislocated to a nearby interstitial site.
Example : Silver halides, ZnS.
(ii) F-centres : The anion vacancy occupied by an electron is called F-centre in Alkali metal halides.
Example : NaCl, KC1, Li Cl.

Question 70.
Calculate the number of unit cells in 8.1 g of aluminium if it crystallizes in a face-centered cubic (f.c.c.) structure. (Atomic mass of Al = 27 g mol-1)

Answer:
1 mole of Aluminium = 27 g = 6.022 × 1023
Hence, No. of atoms present in 27 g of Al
= 6.022×102327
As f.c.c. unit cell contains 4 atoms
∴ No. of f.c.c. unit cells present
= 6.022×1023×8.127×4
= 0.45165 × 1023 = 4.5165 × 1022

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