CBSE PREVIOUS YEAR QUESTION PAPERS (MARCH)- 2012 (SOLVED)

  CHEMISTRY

     

Set I

Time allowed : 3 hours                                                                     

 Maximum Marks: 70

General Instructions:

(i) All questions are compulsory.

(ii) Questions number 1 to 8 are very short - answer questions and carry 1 mark each.

(iii) Questions number 9 to 18 are short - answer questions and carry 2 marks each.

(iv) Questions number 19 to 27 are also short- answer questions and carry 3 marks each.

(v) Question number 28 to 30 are long - answer questions and carry 5 marks each.

(vi) Use Log Tables, if necessary. Use of calculator is not allowed.

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

2. Define 'Peptization'.

3. How is copper extracted from a low grade ore of it ?

4. Which is a stronger reducing agent, SbH3 or BiH3, and why ?

5. What happens when bromine attacks CH2=CH-CH2-C=CH?

6. Write the 1UPAC name of the following :

                                  O

                                 //

CH3-CH2-CH=CH-C-H

7.Write the structure of the product obtained when glucose is oxidized with nitric acid.

8.Differentiate between disinfectants and antiseptics.

9.Express the relation among cell constant, resistance of the solution in the cell and conductivity of the

solution. How is molar conductivity of a solution related to its conductivity ?

Or

The molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9 S cm^2

mol^-1 Calculate the conductivity of this solution.

10.A reaction is of second order with respect to a reactant. How is its rate affected if the concentration of the reactant is (i) doubled (ii) reduced to half ?

11. Which methods are usually employed for purifying the following metals :

(i) Nickel

(ii) Germanium

Mention the principle behind each one of them.

12. Explain the following facts giving appropriate reason in each case :

(i) NF3 is exothermic compound whereas NCl3 is not

(ii) All the bonds in SF4 are not equivalent.

13.Complete the following chemical reaction equations :

(i)Cr2O7^2- I^-H________

(ii)MnO4^- NO2^- H________

14. Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.

15. Explain the following behaviours :

(i)Alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.

(ii)Ortho-nitrophenol is more acidic than ortho-methoxyphenol.

16.Describe the following giving the relevant chemical equation in each case :

(i)Carbylamine reaction

(ii)Hofmann's bromamide reaction.

17.Complete the following reaction equations :

(i)C6H5N2CIH3PO2H2O_____

(ii)C6H5NH2Br(aq)______

18. What are food preservatives ? Name two such substances.

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

calculate the density of copper metal.

(Atomic mass of Cu = 63.55 u and

Avogadro's number NA = 6.02 × 10^23 mol-1)

Or

Iron has a body centered cubic unit cell with the cell dimension of 286.65 pm. Density of iron is 7.87 g cm-3. Use this information to calculate Avogadro's number. (Atomic mass of Fe = 56.0 u).

20.The electrical resistance of a column of 0.05 M NaOH solution of diameter 1 cm and length 50 cm is 5.55 × 10^3 ohm. Calculate its resistivity, conductivity and molar conductivity.

21.The reaction,N2(g)O2(g)__2 NO (g) contributes to air pollution whenever a fuel is burnt in air at a high temperature. At 15000 K, equilibrium constant K for it is 1.0 × 10^-5. Suppose in a case [N2]= 0.80 mol L-1 and [O2] = 0.20 mol L^-1 before any reaction occurs. Calculate the equilibrium concentrations of the reactants and the product after the mixture has been heated to 1500 K.

22.Explain the following terms giving a suitable example for each :

(i) Aerosol

(ii) Emulsion

(iii) Micelle

23.How would you account for the following :

(i) Among lanthanoids, Ln (III) compounds are predominant. However, occasionally in

solutions or in solid compounds, 2 and 4 ions are also obtained

(ii) The E°M^2/M for copper is positive (0.34 V). Copper is the only metal in the first series of transition elements showing this behaviour.

(iii) The metallic radii of the third (5d) series of transition metals are nearly the same as those of the corresponding members of the second series.

24.Name the following coordination entities and draw the structures of their stereoisomers:

(i) [Co(en)2 Cl2] (en = ethane-1,2-diamine)

(ii) [Cr(C2O4)3]^3-

(iii) [CO(NH3)3 Cl3]

(Atomic numbers Cr = 24, Co = 27)

25. Answer the following questions :

(i) What is meant by chirality of a compound ? Give an example.

(ii) Which one of the following compounds is more easily hydrolyzed by KOH and why ?

CH3CHClCH2CH3 or CH3CH2CH2Cl

(iii) Which one undergoes SN2 substitution reaction faster and Why ?

26. What is essentially the difference between a-glucose and 13-glucose ? What is meant by pyranose structure of glucose ?

27.Differentiate between thermoplastic and thermosetting polymers. Give one example of each.

28.(a) Define the following terms :

(i) Mole fraction

(ii) Ideal solution

(b) 15.0 g of an unknown molecular material is dissolved in 450 g of water. The resulting solution

freezes at - 0.34°C. What is the molar mass of the material? (Kr for water = 1.86 K kg mol^-1)

Or

(a) Explain the following :

(i) Henry's law about dissolution of a gas in a liquid.

(ii) Boiling point elevation constant for a solvent.

(b) A solution of glycerol (C3H8O3) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42°C. What mass of glycerol was dissolved to make this solution? (Kb for water = 0.512 K kg mol^-1)

29.(a) Draw the molecular structures of the following compounds :

(i) N2O5 (ii) XeOF4

(b) Explain the following observations :

(i) Sulphur has a greater tendency for catenation than oxygen.

(ii) ICl is more reactive than I2.

(iii) Despite lower value of its electron gain enthalpy with negative sign, fluorine (F2) is a

stronger oxidising agent than Cl2.

Or

(a)Complete the following chemical equations :

(i)CuHNO3(dilute)_____

(ii)XeF4O2F2______

(b) Explain the following observations :

(i) Phosphorus has greater tendency for catenation than nitrogen.

(ii) Oxygen is a gas but sulphur a solid.

(iii) The halogens are coloured. Why ?

30.(a) Write a suitable chemical equation to complete each of the following transformations :

(i) Butan-1-ol to butanoic acid

(ii) 4-Methylacetophenone to benzene-1,4-dicarboxylic acid

(b) An organic compound with molecular formula C9H10O forms 2, 4-DNP derivative, reduces.Tollen's reagent and undergoes Cannizzaro's reaction. On vigorous oxidation it gives 1, 2- benzenedicarboxylic acid. Identify the compound.

Or

(a) Give chemical tests to distinguish between :

(i) Propanol and propanone

(ii) Benzaldehyde and acetophenone

(b) Arrange the following compounds in an increasing order of their property as indicated:

(i) Acetaldehyde,Acetone, Methyl tert-butyl ketone (reactivity towards HCN)

(ii) Benzoic acid, 3, 4-Dinitrobenzoic acid, 4-Methoxybenzoic acid (acid strength)

(iii) CH3CH2CH (Br) COOH, CH3 CH (Br) CH2 COOH, (CH3)2CH COOH (acid strength)