Question

Which substance/ion is oxidised and which substance/ion is reduced in the following reactions?
$PbS+4H_2{O}_2\to PbS{O}_4+4H_{2}O$.

Answer 1

$PbS+4H_2{O}_2\to PbS{O}_4+4H_{2}O$.

Oxidised : $PbS$. The oxidation number of S increases from -2 to +6. Thus, S itself is oxidised and acts as reducing agent.

Reduced: $H_2{O}_2$ The oxidation number of O decreases from -1 to -2. Thus, O itself is reduced and acts as oxidising agent.

Note:
Any species that is oxidised acts as reducing agent.
Any species that is reduced acts as oxidising agent.