Salwan Public School, Gurgaon

Salwan Public School, Gurgaon

Class XII Assignment

Solid State

1.  Differentiate between amorphous and crystalline solids

2.  Why is glass considered a super cooled liquid?

3.  Define the term 'amorphous'. Give a few examples of amorphous solids.

4.  Which solid is used in photovoltaic cells?

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

6.  Ionic solids conduct electricity in molten state but not in solid state. Explain

7.  What type of solids are electrical conductors, malleable and ductile?

8.  (i) What is meant by the term 'coordination number'?

(ii) What is the coordination number of atoms:

(a) in a cubic close-packed structure?

(b) in a body-centred cubic structure?

9. Give the significance of a ‘lattice point’.

10. Name the parameters that characterise a unit cell.

11. Distinguish between

(i) Hexagonal and monoclinic unit cells (ii) Face-centred and end-centred unit cells.

12. How will you distinguish between the following pairs of terms:

(i) Hexagonal close-packing and cubic close-packing? (ii) Crystal lattice and unit cell?

(iii) Tetrahedral void and octahedral void?

13. Calculate the efficiency of packing in case of a metal crystal for

(i) simple cubic (ii) body-centred cubic (iii) face-centred cubic (with the assumptions that atoms are touching each other).

14. What is a semiconductor? Describe the two types of semiconductors and contrast their conduction mechanism.

15. Which of the following lattices has the highest packing efficiency (i) simple cubic (ii) body-centred cubic and (iii) hexagonal close-packed lattice?

16. In terms of band theory, what is the difference

(i) between a conductor and an insulator (ii) between a conductor and a semiconductor?

17. Explain the following terms with suitable examples:

(i) Schottky defect (ii) Frenkel defect (iii) Interstitials and (iv) F-centres.

18. Explain the following with suitable examples:

(i) Ferromagnetism (ii) Paramagnetism (iii) Ferrimagnetism (iv) Antiferromagnetism

(v) 12-16 and 13-15 group compounds.

19. What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?

20. Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an

impurity in it. Explain what impurity defect is.

21. Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the

help of a suitable example.

22. What type of stoichiometric defect is shown by:

(i) ZnS (ii) AgBr

23. A group 14 element is to be converted into n-type semiconductor by doping it with a suitable impurity.

To which group should this impurity belong?

24. Why does ZnO appear yellow on heating? Or Why does ZnO exhibit increased electrical conductivity on heating?

25. Define the terms isotropy and anisotropy.

26. KCl crystals sometimes appear violet. Explain

27. What is the nature of of crystal defect produced when NaCl is doped with MgCl2.

28. What happens when a ferromagnetic substance is subjected to high temperature?

29. What is curie temperature?

30. Why is common salt yellow sometimes instead of white?

31. Why are Frenkel defects not found in pure alkali halides?

32. Why is Frenkel defect found in AgCl?

33. If the radius of the octahedral void is r and radius of the atoms in close packing is R, derive relation

between r and R.

34. Classify each of the following as being either a p-type or a n-type semiconductor: (i) Ge doped with In (ii) B doped with Si.

35. What type of substances would make better permanent magnets, ferromagnetic or ferrimagnetic. Justify

your answer.

36. Explain

(i) The basis of similarities and differences between metallic and ionic crystals.

(ii) Ionic solids are hard and brittle.

37. Explain how much portion of an atom located at (i) corner and (ii) body centre of a cubic unit cell is part of its neighbouring unit cell.

38. Give the significance of a ‘lattice point’.

39. What type of solids are electrical conductors, malleable and ductile?

40. Ionic solids conduct electricity in molten state but not in solid state. Explain.

41. Classify the following solids in different categories based on the nature of intermolecular forces

operating in them: Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite,

rubidium, argon, silicon carbide.

42. Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid,

teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.

43. Why do solids have a definite volume?

44. Why are solids rigid?

45. Refractive index of a solid is observed to have the same value along all directions. Comment on the

nature of this solid. Would it show cleavage property?

46. What makes a glass different from a solid such as quartz? Under what conditions could quartz be

converted into glass?

47.How can you determine atomic mass of an unknown metal if you know its density and dimension of the

unit cell?

Numericals

1.  The face centered unit cell of nickel has an edge length of 352.39 pm. the density of nickel is 8.9g/cm3. Calculate the value of Avogadro number. ( Ni = 58.7) (6.029 x 1023)

2.  CsCl has a body centered cubic lattice with with edge length 412.1 pm and aluminium has face centered cubic lattice with length of the side of unit cell 405pm. Which of the two has higher density? ( Cs= 132.9 ; Al = 29.9) ( Cs = 3.995 g/cm3 Al = 2.7 g/cm3.)

3.  Gold has cubic crystals whose edge length is 407.9 pm. Density of gold is 19.3 g/cm3. Calculate the number of atoms per unit cell and predict the type of crystal structure of gold. (4 : FCC)

4.  An element A (At. Mass = 100) having bcc structure has unit cell edge 400 pm. Calculte the density of A and the number of unit cells in 10 g of A. (5.188 g/cm3 : 3.01x 10 22 unit cells).

5.  Crystalline CsBr has bcc structure. Calculate the edge length if density is 4.24 g/cm3. ( Cs = 133: Br = 80) (436.9pm)

6.  Silver crystallizes in FCC lattice. If the edge length of unit cell is 4.077 x 10-8 cm and density is 10.5 g/cm3, calculate atomic mass of silver. (107.8 amu)

7.  A certain sample of cuprous sulphide is found to have a composition of Cu1.92S because of incorporation of Cu2+ in the lattice. What is the ratio of Cu2+ to Cu+ ? ( 0.043:1)

8.  Calculate the density of silver which crystallizes in the face centered cubic structure. The distance between nearest silver atoms in the structure is 287 pm. (Ag = 107.87) (10.714 g/cm3)

10. If KCl is doped with 10-4 mol% CaCl2, what is the concentration of cationic vacancies? (6.023 x 1017)

Previous Board Questions

2010

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

2.  The density of copper metal is 8.95 g/cm3. If the radius of the copper atom is 127.8 pm,is the copper unit cell simple cubic or body centered cubic or face centered cubic? ( Cu = 63.54 g/mol.)

2009

1.  How do metallic and ionic solids differ in their electrical conductivity?

2.  Silver crystallizes with face centered cubic unit cells. Each side of the unit cell has a length of 409 pm. What is the radius of atom of silver? ( Assume that each face atom is touching the four corner atoms.

2012.

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

2. Copper crystallizes with face centered cubic unit cell. If the radius of copper atom is 127.8 pm, calculate

the density of copper metal.

3. Iron has a body centered cubic unit cell. Density of iron is 7.87g/cm3. Use this information to calculate

the Avogadro number. (Fe = 56.0 u)