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Thursday, 15 October 2015


                                          VSA QUESTIONS (1 MARK)
1. What are Bravais lattices?

2. Why are amorphous solids isotropic in nature?

3. Why glass is regarded as an amorphous solid?

4. Define the term 'crystal lattice.’

5. Name the crystal system for which all four types of unit cells are possible.
[Ans. Orthorhombic]

6. What is the total number of atoms per unit cell in a fcc crystal structure?

[Ans. 4]

7. What difference in behaviour between the glass and sodium chloride would
you expect to observe, if you break off a piece of either cube?

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 atoms is double to B, so it occupied tetrahedral void]

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 < simple cubic]

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. Write dimensions and bond angles of match-box type of unit cells.
[Hint : Orthorhombic crystal system].

17. Calculate the number of atoms in a cubic unit cell having one atom on
each corner and two atoms on each body diagonal.
[Hint : No. of atoms = 8 × 1/8 + 4 × 2 = 9]

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

19. In Corundum, O2– ions fromhcp and Al3+ occupy two third of octahedral
voids. Determine the formula of corundum. [Ans. : Al2O3]

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

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

22. Define the term ‘doping’.

23. Why does conductivity of Silicon increase with the rise in temperature.

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

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

26. Which Point defect in ionic crystal does not alter the density of the relevant

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

28. Which type of defects are known as thermodynamic defects?
[Ans. : Stoichiometric defects]

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

30. 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]


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 two consequences.

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 becomes 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 located at (a) corner (b) body centre
(c) face-centre and (d) edge centre of a cubic unit cell, is part of its
neighbouring unit cells.

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 corners, what is the formula of the

12. A compound made up of elements ‘A’ and ‘B’ crystallises in a cubic close packed structure. Atom 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?

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.

1. Sodium crystallises in a bcc unit cell. What is the approximate number of
unit cells in 4.6 g of sodium? Given that the atomic mass of sodium is 23
g mol–1. 

2. In a crystalline solid anions ‘C’ are arranged in cubic close packing, cations
‘A’ occupy 50% of tetrahedral voids and cations ‘B’ occupy 50% of octanedral
voids. What is the formula of the solid? 

3. A metal crystalises into two cubic lattices fcc and bcc, whose edge lengthare 3.5Å and 3.0Å respectively. Calculate the ratio of the densities of fcc and bcc lattices. 

5. An element of atomic mass 98.5 g mol–1 occurs in fcc structure. If its unit
cell edge length is 500 pm and its density is 5.22 g cm–3. Calculate the
value of Avogadro constant. [Ans. : 6.03 × 1023 mol–1]

6. An element crystallises in a cubic close packed structure having a fcc unit
cell of an edge 200 pm. Calculate the density if 200 g of this element
contain 24 × 1023 atoms. [Ans. : 41.6 g cm–3]

7. A fcc unit cell containing atoms of element (molar mass 60.4 g mol–1) has
cell edge 4 × 10–8 cm. Calculate the density of unit cell.[Ans. : 6.23 g/cm3]

8. The metal calcium (atomic mass = 40 gm mol–1] crystallises in a fcc unit
cell with a = 0.556 nm. Calculate the density of the metal if (i) It contains
0.2% Frenkel defect. (ii) It contains 0.1% schottky defect.
[Ans. : (i) 1.5463 g/cm3; (ii) 1.5448g/cm3]

9. Analysis shows that a metal oxide has a empirical formula M0.96O. Calculate the percentage of M2+ and M3+ ions in this crystal.
[Ans. : M2+ = 91.7%, M3+ = 8.3%]

10. AgCl is doped with 10–2 mol% of CdCl2, find the concentration of cation vacancies. [Ans. : 6.02 × 1019 mol]

11. A metallic element has a body centered cubic lattice. Edge length of unit
cell is 2.88 × 10–8 cm. The density of the metal is 7.20 gcm–3. Calculate
(a) The volume of unit cell.
(b) Mass of unit cell.
(c) Number of atoms in 100 g of metal.
[Ans. : (a) 2.39 × 10–23 cm3 (b) 1.72 × 10–22 g, (c) 1.162 × 1024 atoms]

12. Molybednum has atomic mass 96 g mol–1 with density 10.3 g/cm3. The
edge length of unit cell is 314 pm. Determine lattice structure whether
simple cubic, bcc or fcc.
(Given NA = 6.022 × 1023 mol–1) [Ans. : Z = 2, bcc type]

13. The density of copper metal is 8.95 g cm–3. If the radius of copper atom
is 127 pm, is the copper unit cell a simple cubic, a body-centred cubic or
a face centred cubic structure?
(Given at. mass of Cu = 63.54 g mol–1 and NA = 6.02 × 1023 mol–1]

14. The well known mineral fluorite is chemically calcium fluoride. It is known
that in one unit cell of this mineral there are 4 Ca2+ ions and 8F– ions and
that Ca2+ ions are arranged in a fcc lattice. The F– ions fill all the tetrahedral
holes in the fcc lattice of Ca2+ ions. The edge of the unit cell is 5.46 × 10–
8 cm in length. The density of the solid is 3.18 g cm–3 use this information
to calculate Avogadro’s number (Molar mass of CaF2 = 78.08 g mol–1]
[Ans. : 6.02 × 1023 mol–1]

Chemistry for class 12 ...........
enzyme-catalysis regulation

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