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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). |
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Answer» Solution :(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. |
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