Give suitable reasons for the following statements:
(i) Rain water conducts electricity but distilled water does not.
(ii) We feel burning sensation in the stomach when we over seat.
(iii) A tarnished copper vessels regain its shine when rubbed with lemon.
(iv) The crystals of washing soda change to white powder on exposure to air.

Explanation

(i) Distilled water does not conduct electricity because it does not contain any ionic compound like acids, bases or salts dissolved in it.
(ii) When we over eat, excess of acid is produced in the stomach which causes burning sensation.
(iii) Copper vessels tarnish due to formation of basic copper carbonate which gets neutralized when rubbed with lemon and the copper vessels regains its shine.
(iv) Washing soda is sodium carbonate decahydrate which when exposed to air loses 10 molecules of water and changes to white powder.