Give reasons for the following observations:
(i) Ionic compounds in general have high melting and boiling points.
(ii) Highly reactive metals cannot be obtained from their oxides by heating them with carbon.
(iii) Copper vessels get a green coat when left exposed to air in rainy season.
Reasons:
(i) Ionic compounds in general have high melting and boiling points due to strong electrostatic force of attraction between them.
(ii) Highly reactive metals like Na, K, Ca cannot be obtained from their oxides by heating them with carbon because these metals have higher affinity for oxygen. Therefore, they are isolated from their fused chloride by passing electric current.
(iii) When copper vessels left exposed to air in rainy season, the metals react with gases and moisture present in air to form a mixture of copper carbonate and copper hydroxide. This gives a green colour to the vessels.