Question

Give reasons:

(i) Copper vessels develop a green coating when exposed in air.(ii) Acids like HCl and HNO3 show acidic characters in aqueous solutions while solutions of compound like alcohol and glucose do not show acidic character.(iii) Dry HCl gas does not change the colour of the dry litmus paper

Answer 1

(i) 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.

(ii) Acids like HCl and HNO₃ show acidic character by releasing H+ ions in water. Similarly, alcohols also show acidic behaviour, however strength of their acidity is less and also varies in different alcohols. In glucose, there is no release of H+ ions -in the solution. Hence it is- neutral.

(iii) Dry.HCl do not change colour of litmus paper because there is no release of H⁺ ions which is cause of acidity and change of colour of litmus.