(e) Give reasons why:
(i) Hot water has no action on aluminium.
(ii) Concentrated nitric acid makes iron passive.
(iii) Cryolite and fluorspar are added to alumina, in the metallurgy of aluminium.
(iv) Metals are good reducing agents.
(v) Carbon tetrachloride does not dissolve in water.

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Solution

(i) Aluminium has a hard yet thin oxide layer over its surface, which prevents it from reacting with hot water.
(ii) Concentrated nitric acid is a powerful oxidising agent. It leads to the formation of a thin yet hard oxide layer on the surface of iron, thereby inhibiting further reactions.
Fe + 6HNO₃ → Fe(NO₃)₂ + 3H₂O + 3NO₂
(iii) Cryolite and fluorspar are added to alumina because of the following reasons:
(a) They increase the conductivity of the molten mixture during electrolytic extraction of aluminium from alumina.
(b) They decrease the melting point of alumina.
(c) Fluorspar help in the mobility of the fused mixture.
(d) Cryolite acts as solvent for the electrolytic mixture.

(iv) Metals donate electrons easily; hence, they are known as reducing agents.
(v) Carbon tetrachloride is non-polar; hence, it does not dissolve in a polar solvent like water.

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Q. Give reasons for the following:
(i) In laboratory preparation of nitric acid all the apparatus including cork should be made up of glass.
(ii) Commercial nitric acid is yellow in colour, but when it is diluted with water, it turns colourless.
(iii) Aluminium does not react with nitric acid of any concentration.
(iv) Conc. nitric acid renders iron passive.
(v) Nitric acid is used in purification of gold.
(vi) Aqua regia dissolves gold and platinum.
(vii) Nitric acid usually does not yield hydrogen from acids.
(viii) Lightning is a blessing in disguise.
(ix) Concentrated nitric acid is brown in colour.
(x) Concentrated nitric acid is a stronger oxidizing agent.

Explain the reason why:
(i) HCl gas fumes in moist air.
(ii) Dilute HCl cannot be concentrated beyond 22.2% by distillation.
(iii) Dilute acids are stronger electrolytes as compared to concentrated acid.
(iv) Liquid ammonia has no action on litmus while liquor ammonia has an effect.
(v) Ammonia is not collected over water.
(vi) Pure nitric acid does not dissolve gold or platinum, but aqua regia dissolves them.

Q. Explain the following:
(i) Galvanisation protects iron from rusting.
(ii) Stainless steel is more useful than steel.
(iii) Aluminium is extensively used for making aircraft parts.
(iv) Hot water has no action on aluminium.

Q. Give the reasons for the following:
(i) Zinc is used in galvanisation and dry cells.
(ii) Nitric acid can be stored in aluminium containers.
(iii) Aluminium oxide cannot be reduced by carbon.
(iv) A neutral gas other than oxygen is formed at the anode during electrolysis of fused alumina.
(v) Extraction of aluminium was very difficult in the beginning.
(vi) Carbon anodes are used in the electrolytic extraction of aluminium.
(vii) Galvanized metal ions should not be used for storing food.

(c) Write balanced equations for the following reactions:
(i) dissolving sulphur trioxide in water.
(ii) Aluminium powder is warmed with hot and concentrated caustic soda solution.
(iii) Concentrated nitric acid is added to copper turnings kept in a beaker.
(iv) Red lead (trilead tetroxide) is warmed with concentrated hydrochloric acid.

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(e) Give reasons why: (i) Hot water has no action on aluminium. (ii) Concentrated nitric acid makes iron passive. (iii) Cryolite and fluorspar are added to alumina, in the metallurgy of aluminium. (iv) Metals are good reducing agents. (v) Carbon tetrachloride does not dissolve in water.

(e) Give reasons why:
(i) Hot water has no action on aluminium.
(ii) Concentrated nitric acid makes iron passive.
(iii) Cryolite and fluorspar are added to alumina, in the metallurgy of aluminium.
(iv) Metals are good reducing agents.
(v) Carbon tetrachloride does not dissolve in water.