CBSE Class 12 Chemistry The Solid State Notes Set C

THE SOLID STATE

QUESTIONS

1. What are anistropic substances.

2. Why are amorphous solids isotropic in nature?

3. Why glass is regarded as an amorphous solid?

4. Define the term 'crystal lattice.’

8. Define the term voids.

9. What type of stochiometric defect is shown by (i) ZnS and (ii) CsCl?

[Hint. : (i) Frenkel defect (ii) Schottky defect]

*10. If the formula of a compound is A₂B, which sites would be occupied by A ions?

[Hint. : Number of A ions is double to B ions, so ions will occupy tetrahedral voids]

11. What is the coordination number for

(a) an octahedral void

(b) a tetrahedral void.

[Hint. : (a) 6; (b) 4 ]

*12. How many octahedral voids are there in 1 mole of a compound having cubic closed packed structure? [Ans. : 1 mole]

13. Arrange simple cubic, bcc and fcc lattice in decreasing order of the fraction of the unoccupied space.

[Hint. : fcc < bcc < sc]

14. How much space is empty in a hexagonal closed packed solid?

15. An element crystallises separately both in hcp and ccp structure. Will the two structures have the same density? Justify your answer.

[Hint : Both crystal structures have same density because the percentage of occupied space is same.]

16. In NaCl crystal, Cl^– ions form the cubic close packing. What sites are occupied by Na⁺ ions.

17. In Corundum, O^2– ions from hcp and Al³⁺ occupy two third of octahedral voids. Determine the formula of corundum. [Ans. : Al₂O₃]

18. Why is Frenkel defect not found in pure alkali metal halides?

19. Which point defect is observed in a crystal when a vacancy is created by an atom missing from a lattice site.

20. Define the term ‘doping’.

21. Why does conductivity of silicon increase with the rise in temperature.

22. Name the crystal defect which lowers the density of an ionic crystal. [Ans. : Schottky defect]

23. What makes the crystal of KCl sometimes appear violet? [Hint : F-Centre]

24. Which point defect in ionic crystal does not alter the density of the relevant solid?

25. Name one solid in which both Frenkel and Schottky defects occur.

26. Which type of defects are known as thermodynamic defects?

[Ans. : Stoichiometric defects]

27. In a p-type semiconductor the current is said to move through holes. Explain.

28. Solid A is very hard, electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it?

[Hint : Covalent solid]

SA (I) TYPE QUESTIONS (2 - MARK QUESTIONS)
1. List four distinctions between crystalline and amorphous solids with one example of each.

2. Give suitable reason for the following–
(a) Ionic solids are hard and brittle.
(b) Copper is malleable and ductile.

3. Define F–centre. Mention its one consequence.

4. What is packing efficiency. Calculate the packing efficiency in body-centered cubic crystal.

5. Explain :
(a) List two differences between metallic and ionic crystals.
(b) Sodium chloride is hard but sodium metal is soft.
6. Account for the following :
(a) Glass objects from ancient civilizations are found to become milky in appearance.
(b) Window glass panes of old buildings are thicker at the bottom than at the top.

7. Why is graphite soft lubricant and good conductor of electricity?

8. What do you understand by the following types of stacking sequences :
(a) AB AB ............... (b) A B CABC .................
What kind of lattices do these sequences lead to?

9. Derive the formula for the density of a crystal whose length of the edge of the unit cell is known?

10. Explain how much portion of an atom is located at (a) corner (b) body centre (c) face-centre and (d) edge centre of a cubic unit cell.

*11. In a fcc arrangement of A and B atoms A are present at the corners of the unit cell and B are present at the face centres. If one atom of A is missing from its position at the corner, what is the formula of the compound?
[Ans. : A7B24]

*12. A compound made up of elements ‘A’ and ‘B’ crystallises in a cubic close packed structure. Atoms A are present on the corners as well as face centres, whereas atoms B are present on the edge-centres as well as body centre. What is the formula of the compound? [Ans. AB]
13. Explain the terms :
(a) Intrinsic semiconductor
(b) Extrinsic semiconductor.

14. Explain how vacancies are introduced in a solid NaCl crystal when divalent cations are added to it.

15. What is meant by non-stoichiometric defect? Ionic solids which have anionic vacancies due to metal excess defect develop colour. Explain with the help of suitable example.

16. Define the term ‘point defects’ Mention the main difference between stoichiometric and non-stoichiometric point defects.

THE SOLID STATE (2 - MARK QUESTIONS)

17. A compound MpXq has cubic close packing (ccp) arrangement of X. Its unit cell structure is show below :
Determine the empirical formula of the compound. [Ans : MX2]

18. The concentration of cation vacancies in NaCl crystal doped with CdCl2 is found to be 6.02 x 1016 mol–1. What is the concentration of CdCl2 added to it? [Ans : 10–5 mol% CdCl2]

19. Iron changes its crystal structure from body contred to cubic close backed structure when heated to 916°C. Calculate the ratio of the density of the BCC crystal to that of CCP crystal. Assume that the metallic radius of the atom does not change.

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