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Question:
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In which of the following reactions of \(\mathrm{H}_2 \mathrm{O}_2\) acts as an oxidising agent (either in acidic, alkaline or neutral medium)?
(i) \(2 \mathrm{Fe}^{2+}+\mathrm{H}_2 \mathrm{O}_2 \rightarrow\)
(ii) \(2 \mathrm{MnO}_4^{-}+6 \mathrm{H}^{+}+5 \mathrm{H}_2 \mathrm{O}_2 \rightarrow\)
(iii) \(\mathrm{I}_2+\mathrm{H}_2 \mathrm{O}_2+2 \mathrm{OH}^{-} \rightarrow\)
(iv) \(\mathrm{Mn}^{2+}+\mathrm{H}_2 \mathrm{O}_2 \rightarrow\)
Options:
(i) \(2 \mathrm{Fe}^{2+}+\mathrm{H}_2 \mathrm{O}_2 \rightarrow\)
(ii) \(2 \mathrm{MnO}_4^{-}+6 \mathrm{H}^{+}+5 \mathrm{H}_2 \mathrm{O}_2 \rightarrow\)
(iii) \(\mathrm{I}_2+\mathrm{H}_2 \mathrm{O}_2+2 \mathrm{OH}^{-} \rightarrow\)
(iv) \(\mathrm{Mn}^{2+}+\mathrm{H}_2 \mathrm{O}_2 \rightarrow\)
Solution:
2946 Upvotes
Verified Answer
The correct answer is:
(i), (iv)
Let us complete the reactions :
(i) \(\mathrm{Fe}^{2+}+\mathrm{H}_2 \mathrm{O}_2^{-} \longrightarrow \mathrm{Fe}^{3+}+\mathrm{H}_2 \mathrm{O}^{2-}\)
(ii) \(\mathrm{Mn}^{7+} \mathrm{O}_4^{-}+\mathrm{H}^{+}+\mathrm{H}_2 \mathrm{O}_2^{-} \longrightarrow \mathrm{Mn}^{2+}+\mathrm{O}_2^0+\mathrm{H}_2 \mathrm{O}\)
(iii) \(\mathrm{I}_2^0+\mathrm{H}_2 \mathrm{O}_2^{-}+\mathrm{OH}^{-} \longrightarrow \mathrm{I}^{-}+\mathrm{O}_2^0+\mathrm{H}_2 \mathrm{O}\)
(iv) \(\mathrm{Mn}^{2+}+\mathrm{H}_2 \mathrm{O}_2^{-} \longrightarrow \mathrm{Mn}^{4+}+\mathrm{OH}^{-}\)
In reactions, \(\mathrm{Fe}^{2+}\) of (i) and \(\mathrm{Mn}^{2+}\) of (iv) get oxidised to \(\mathrm{Fe}^{3+}\) and \(\mathrm{Mn}^{4+}\) respectively by \(\mathrm{H}_2 \mathrm{O}_2\), which itself is reduced to \(\mathrm{H}_2 \mathrm{O}\).
(i) \(\mathrm{Fe}^{2+}+\mathrm{H}_2 \mathrm{O}_2^{-} \longrightarrow \mathrm{Fe}^{3+}+\mathrm{H}_2 \mathrm{O}^{2-}\)
(ii) \(\mathrm{Mn}^{7+} \mathrm{O}_4^{-}+\mathrm{H}^{+}+\mathrm{H}_2 \mathrm{O}_2^{-} \longrightarrow \mathrm{Mn}^{2+}+\mathrm{O}_2^0+\mathrm{H}_2 \mathrm{O}\)
(iii) \(\mathrm{I}_2^0+\mathrm{H}_2 \mathrm{O}_2^{-}+\mathrm{OH}^{-} \longrightarrow \mathrm{I}^{-}+\mathrm{O}_2^0+\mathrm{H}_2 \mathrm{O}\)
(iv) \(\mathrm{Mn}^{2+}+\mathrm{H}_2 \mathrm{O}_2^{-} \longrightarrow \mathrm{Mn}^{4+}+\mathrm{OH}^{-}\)
In reactions, \(\mathrm{Fe}^{2+}\) of (i) and \(\mathrm{Mn}^{2+}\) of (iv) get oxidised to \(\mathrm{Fe}^{3+}\) and \(\mathrm{Mn}^{4+}\) respectively by \(\mathrm{H}_2 \mathrm{O}_2\), which itself is reduced to \(\mathrm{H}_2 \mathrm{O}\).
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