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Question

Give reasons for:

a) Platinum, gold and silver are used to make jewellery.

b) Sodium, potassium and lithium are stored under oil.

c) Aluminium is a highly reactive metal, yet it is used to make utensils.

d) Carbonate and sulphide ores are usually converted into their oxides during the process of extraction.

e) Copper vessels, when exposed to air, form a greenish coating all around.

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Solution

(a) Platinum, gold and silver are used to make jewellery because these are low reactive metals so rarely corrosion occur (In silver) and hence do not lost their shine and lustre.

(b) The reaction of these substances with oxygen is highly exothermic which may cause fire, also they react with water to form base so they are kept in oil.

(c) This is because aluminium is good conductor of heat and electricity. To prevent its reaction with food at high temperature a protective layer of aluminium oxide (Al2O3 ) is formed which prevent further corrosion.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because it is easier to obtain metal from its oxide as compared with its sulphides or carbonates ore.

(e) Copper metal when exposed to air turns green in colour due to corrosion. Thus, when copper vessels are exposed to air in rainy season for sometime, the metal reacts with gases and moisture present in air to form a mixture of copper carbonate and copper hydroxide [(CuCO3). Cu(OH)2]. This gives a green colour to the vessels.

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