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

                                                         CHEMISTRY

                                                              Set III

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.What are n-type semiconductors ?

2.Define `peptization'.

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

4.What is the basicity of H3PO2 acid and why ?

5.Write the IUPAC name of the following :

6.Write the IUPAC name of the following :

7.Write a reaction which shows that all the carbon atoms in glucose are linked in a straight chain.

8. What is the cause of a feeling of depression in human beings ? Name a drug which can be

useful in treating this depression.

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. Explain the role of each of the following :

(i) NaCN in the extraction of silver

(ii) SiO2 in extraction of copper.

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)C6H5NH2Br2(aq)→

18.Differentiate between disinfectants and antiseptics. Give one example of each group.

19.Copper crystallises with face centred 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 × 1023 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.Write three distinct features of chemisorptions which are not found in physisorptions.

23.Explain each of the following observations :

(i) With the same d-orbital configuration (d^4), Cr^2 is a reducing agent while Mn^3 is an oxidising agent.

(ii)Actinoids exhibit a much larger number of oxidation states than the lanthanoids.

(iii)There is hardly any increase in atomic size with increasing atomic numbers in a series of

transition metals.

24. Name the following coordination entities and describe their structures :

(i ) [Fe(CN)6]^4-

(ii) [Cr(NH3)4 Cl2]^

(iii) [Ni (CN)4]^2-

(Atomic numbers Fe = 26, Cr = 24, Ni = 28)

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. Define the following as related to proteins :

(i) Peptide linkage

(ii) Primary structure

(iii) Denaturation

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)