Give reasons for following:-
(i) ZnO issued as white paint inspite of the fact that it has less covering power than white lead.
(ii) Zn readily liberates `H_(2)` from cold, dil `H_(2)SO_(4)` but not from cold, conc. `H_(2)SO_(4)`.

Explanation

(i) White lead pigments are backened after sometime due to the action of `H_(2)S` present in atmosphere where as ZnO pigments are not affected by `H_(2)S` and remains white `4PbO + H_(2)S to PbSO_(4) + H_(2)`
(ii) `H_(2)SO_(4)` is a covalent compound which in dilute solution ionises to appreciable extent to produce `H^(+)` ions and thus Zn reacts with dilute `H_(2)SO_(4)` to produce `H_(2)`.
`Zn + 2H^(+) to Zn^(+2) + H_(2)`
On the other hand the dissociation of `H_(2)SO_(4)` in conc. solution is not appreciable.