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ISC Class 12 Chemistry Solved Question Paper 2008

Short Answer Type

31.

Write balanced equations for each of the following reactions :

(i) Silver Sulphide and Sodium Cyanide.

(ii) Water is added to aluminium chloride.

(iii) Bromine water and sodium sulphite.

(iv) Phosphorous is boiled with a solution of sodium hydroxide.

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32.

How will you bring about the following conversions :

(i) Chloroacetic acid to Glycine.

(ii) Formic acid to Oxalic acid.

(iii) Diethyl ether to ethanol.

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33. Draw the resonating structures of Chlorobenzene.

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34.

State the reagents for the following conversions:

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35.

Give one example each of the following name reactions :

(i) Hofmann’s Degradation

(ii) Cannizzaro’s Reaction

(iii) Benzoin Condensation

(iv) Friedel Craft’s Reaction.

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36.

How will you distinguish between the following pairs of compounds ? Give one good chemical test.

(i) Glucose and Sucrose
(ii) Ethanol and Phenol

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37.

Write balanced equations of the following reactions :

(i) Aniline and Bromine water

(ii) Ethylamine and Nitrous Acid

(iii) Acetic Anhydride and Ammonia

(iv) Acetone and Phosphorous Pentachloride.

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38. Give one example each of addition and condensation polymer. Name the monomers in each case.

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Long Answer Type

39. Name the chief ore of tin. Describe the extraction of tin from the concentrated ore.

The chief ore of tin is galena (PbS). Lead is extracted from galena by pyrometallurgy. The following steps are involved in the extraction of lead from galena. When the ore is rich in lead, and method is called self-reduction iron process.

(i) Roasting : The concentrated and crushed ore is heated below 1023 K in excess of air in a reverberatory furnace. As a result, PbS is partly oxidised to PbO and PbSO₄.

2PbS + 3O₂ ----> 2PbO +2SO₂
(Galena) (Lead Oxide)

PbS +2O₂ ---> PbSO₄
(lead sulphate)

(ii) Reduction : The roasted ore is now heated in a limited supply of air at a higher temperature (which is equal to fusion temperature). Excess of galena is added in the furnace. It results in a reduction of PbS0₄ and PbO to Pb.

PbSO₄ +PbS ----> 2Pb +2SO₄
2PbO +PbS -----> 3Pb +SO₂

The molten lead settles at the bottom of the furnace and drawn off from there.

When galena is poor in lead, it is extracted by carbon reduction process. Following steps are involved in it.

(i) Roasting and sintering : The concentrated galena is taken to a special type of furnace called sinterner. Galena is heated in excess of air.

2PbS +3O₂ ---> 2PbO +2SO₂

ii) Smelting : The sintered ore is mixed with coke (fuel) and lime (flux) and taken to the blast furnace. When the blast of air is passed into this mixture, following reactions take place in a blast furnace.

PbO +C ---> Pb +CO

PbO +CO ----> Pb +CO₂

CaO +SiO2 ---> CaSiO₃

Molten slag and molten lead are removed via separate hole in a blast furnace.

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