Why do the following reactions proceed differently? `Pb_(3)O_(4)+8HClrarr3PbCl_(2)+Cl_(2)+4H_(2)O` and `Pb_(3)O_(3)+4HNO_(3)rarr 2Pb(NO_(3))_(2)+PbO_(2)+2H_(2)O`

Explanation

`Pb_(3)O_(4)` is actually a stoichiometric mixture of 2 mol, of PbO and 1 mol. Of `PbO_(2)`"in"`PbO_(2)` lead is present in +4 oxidation state, whereas the stable oxidation state of lead in PbO is + 2. `PbO_(2)` thus can act as an oxidant (oxidising agent) and therefore, can oxidise Cl ion of HCl into chlorine. We may also keep in mind that PbO is a basic oxide. Therefore the reaction
`Pb_(3)O_(4)+8HCl to 3PbCl_(2)+Cl_(2)+4H_(2)O`
can be splitted into two reactions namely:
`2PbO+4HCl to 2PbCl_(2)+2H_(2)O` (acid base reaction )
+4 -1 +2 0
`PbO_(2)+4HCl to PbCl_(2)+Cl_(2)+2H_(2)O` (redox reaction )