Question
How does Cu2O act as both oxidant and reductant? Explain with proper reactions showing the change of oxidation numbers in each example.
✓
Answer
Cu+ undergoes disproportionation to form Cu2+ and Cu. $2\text{Cu}^+(\text{aq})\xrightarrow{\ \ \ \ }\text{Cu}^{2+}(\text{aq})+\text{Cu}(\text{s})$ Thus, Cu+ or Cu2O acts both as an oxidant as well as reductant.
- When heated in air, Cu2O is oxidised to CuO.
$\stackrel{+1\ \ \ \ \ \ }{\text{Cu}_2}\stackrel{-2\ \ \ }{\text{O}}+\frac12\stackrel{0\ \ \ }{\text{O}_2}\xrightarrow{\ \ \ \ \ \ }2\stackrel{+2\ \ \ \ }{\text{Cu}}\stackrel{-2\ \ }{\text{O}}$
i.e. Cu2O acts as a reductant and reduces O2 to O2-.
- When heated with Cu2S, it oxidises S2- to SO2 and hence, Cu2O acts as an oxidant.
$2\stackrel{+1\ \ \ \ \ \ }{\text{Cu}_2}\stackrel{-2}{\text{O}}+\stackrel{+1\ \ \ \ \ }{\text{Cu}_2}\stackrel{-2}{\text{S}}\xrightarrow{\ \ \ \ \ \ }6\stackrel{0\ \ \ \ \ \ }{\text{Cu}}+\stackrel{+4\ \ \ \ \ \ \ }{\text{SO}_2}$
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