Question

State reasons for the following:
(a) Zinc oxide is an amphoteric oxide.
(b) Sodium metal is stored in bottle filled with kerosene oil.
(c) In the reactions of nitric acid with metals, generally hydrogen gas is not evolved.

Answer 1

(a).Zinc oxide (ZnO) is classified as an amphoteric oxide because it exhibits both acidic and basic properties. It can react with both acids and bases. For example, it reacts with hydrochloric acid to form zinc chloride (\(ZnCl_2\)) and with sodium hydroxide to form sodium zincate (\(Na_2ZnO_2\)).

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(b).Sodium is a highly reactive metal that reacts vigorously with oxygen and water. To prevent it from reacting with moisture in the air or any water it might come into contact with, it is stored under kerosene oil, which prevents its contact with air and moisture.

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(c).When nitric acid reacts with metals, hydrogen gas is generally not produced because the nitrate ion (\(NO_3^-\)) in nitric acid is a strong oxidizing agent. It tends to oxidize the hydrogen produced in the reaction to water and instead, different nitrogen oxides (like \(NO,\ NO_2,\ or \  N_2O\)) might be formed depending on the concentration of the acid and the nature of the metal.