CBSE Board Class 12 Chemistry Previous Year Question Papers 2008

CHEMISTRY (Theory)
Time allowed : 3 hours Maximum Marks : 70

General Instructions :
(i) All  questions are compulsory.
(ii) Marks for each question are indicated against it.
(iii) Question number  1 to  5 are very short-answer questions, carrying  1 mark each.
Answer these in one word or about one sentence each.
(iv) Question number  6 to  12 are short-answer questions, carrying 2 marks each.
Answer these in about  30 words each.
(v) Question number  13 to  24 are short-answer questicms of  3 marks each. Answer
these in about  40 words each.
(vi) Question number  25 to  27are long-answer questions of  5 marks each. Answer
these in about  70 words each.
(vii) Use Log Tables, if necessary. Use of calculators is not permitte

1. What is the coordination number in a rock salt type structure ? 1

2. State Raoult’s law for a binary solution containing volatile components. 1

3. What is meant by order of a reaction being zero ? 1

4. Write the IUPAC name of the following compound : 1
(CH3 ) 3 CCH2 COOH

5. Mention one commercial use of N,N-Dimethylaniline (DMA). 1

6. State as a mathematical formula the de Broglie relationship for moving particles. What
experimental evidence is available for this concept ? 2
OR
Specify the ranges of values for quantum numbers m l and m s for an electron in an atom when the n quantum number value for it is 2. What is the significance of these values for the orbitals ? 2

7. When can an endothermic process be spontaneous ? Give an example of such a process. 2

8. Write balanced chemical equations for the following reactions : 2

9. Explain any  one  of the following statements : 2
(i) The transition metals are well known for the formation of interstitial compounds.
(ii) The largest number of oxidation states are exhibited by manganese in the first
series of transition elements.

10. Draw the three dimensional representations of (R)- and (S)- butan-2-ol. 2

11. Write chemical reaction equations to illustrate the following reactions : 2
(i) Williamson synthesis of ethers
(ii) Reimer-Tiemann reaction

12. Distinguish between addition polymers and condensation polymers and give one example
of each class. 2

13. Answer the following in the light of MO theory : 3
(a) Which has a higher bond order, C 2?
or 
(b) Which species is not likely to exist, Li 2or Be 2 ?
                                   OR
(a) Compare the structural shapes of the following species :
SF 6   and  SF 4
(b) What type of intermolecular forces exist between Cl 2 and CBr 4 present in a mutual solution ? 3

14. (a) Name an element with which silicon can be doped to give an n-type semiconductor.
(b) Which type of crystals exhibits piezoelectricity ? 3

15. The vapour pressure of water is 12.3 kPa at 300 K. Calculate the vapour pressure of a
one molal solution of a non-volatile non-ionic solute in water. 3

16. Using the values of
and  , given herein, calculate the standard molar Gibbs
energy of formation,

17. The   rates of most reactions double when   their temperature is raised from 298 K to
308 K. Calculate activation energy of such a reaction. 3
(R = 8.314 J mol _1 K _ 1  log 2 = 0.3010)

18. State what is observed when
(i) the electrodes connected to a battery are dipped into a sol.
(ii) an  electrolyte solution is added to a sol.
(iii) an  emulsion is subjected to high speed centrifugation. 3

19. Answer the following questions : 3
(i) Which element in the first series of transition elements does not exhibit variable
oxidation states and why ?
(ii) What happens when a solution of copper (II) sulphate is saturated with ammonia ?
(iii) Why do actinoids, in general, exhibit a greater range of oxidation states than the
lanthanoids ?

20. (a) Illustrate the following with an example each :
(i) Linkage isomerism
(ii) Coordination isomerism
(b) Why is [NiCl 4 ]2

21. Write the nuclear reactions for the following radioactive changes : 3
(i) undergoes  α-decay
(ii)  undergoes  β _-decay
(iii) undergoes K-decay

22. Explain the mechanism of nucleophilic addition to a carbonyl group and give one example
of such addition reactions. 3

23. Write the chemical equations for the following chemical reactions : 3
(a) 1-Nitropropene is prepared from acetaldehyde
(b) Benzonitrile is converted to acetophenone
(c) A primary amine is prepared from a primary alkyl halide

24. Mention one important use of each of the following : 3
(i) Equanil
(ii) Sucralose
(iii) Carbon fibres

25. (a) Write the formulation for the galvanic cell in which the reaction,
Cu (s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag (s)   takes place.
Identify the cathode and the anode reactions in it.
(b) Write Nernst equation and calculate the emf of the following cell :
Sn (s) | Sn 2+ (0.04 M) || H + (0.02 M) | H 2 (g) (1 bar) | Pt (s) (Given    ) 2, 3
OR
(a) Explain with one example each the terms weak and strong electrolytes.
(b) Write the Nernst equation and calculate the emf of the following cell :
Fe (s) | Fe 2+ (0-001 M) || H + (1 M) | H 2 (g) (1 bar) | Pt (s) (Given   ) 2, 3

26. (a) How would you account for any  two  of the following :
(i) PbO2 is a stronger oxidising agent than SnO 2
(ii) H3 PO2 acts as a monobasic acid.
(iii) The pKa value for HOCl is higher than that of HOClO.
(b) Draw the structures of the following species :
(i)     Peroxodisulphuric acid, H 2 S 2 O8
(ii)    Xenon tetrafluoride, XeF 4 2, 3
                OR
(a) Assign reasons for any  two  of the following observations :
(i) The lower oxidation state becomes more stable with increasing atomic number
in Group 13.
(ii) Hydrogen iodide is a stronger acid than hydrogen fluoride in aqueous solution.
(iii) The basic character among the hydrides of Group 15 elements decreases with
increasing atomic numbers.
(b) Draw the structural formula for  XeOF

27. (a) Name   the   three    major   classes    of   carbohydrates    and    give   the    distinctive
characteristic of each class.
(b) What  are  nucleotides  ?  Name  two  classes  of nitrogen  containing  bases  found
amongst nucleotides. 3, 2
OR
(a) Describe the classification of lipids based on their chemical compositions. Mention
the chief chemical characteristic of each class.
(b) Explain the term ‘mutarotation’. 3, 2