JEE MAIN - Chemistry (2022 - 30th June Morning Shift - No. 4)
In which of the following half cells, electrochemical reaction is pH dependent?
$$Pt\,|\,F{e^{3 + }},\,F{e^{2 + }}$$
$$MnO_4^ - \,|M{n^{2 + }}$$
$$Ag\,|\,AgCl\,|C{l^{ - 1}}$$
$${1 \over 2}{F_2}\,|{F^ - }$$
Explanation
Reduction of $\mathrm{MnO}_{4}^{-}$ is $\mathrm{pH}$ dependent.
In acidic medium
$$ \mathrm{MnO}_{4}^{-}+5 \mathrm{e}^{-} \longrightarrow \mathrm{Mn}^{2+} $$
In neutral medium
$$ \mathrm{MnO}_{4}^{-}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Mn}^{4+} $$
In basic medium
$$ \mathrm{MnO}_{4}^{-}+\mathrm{e} \longrightarrow \mathrm{Mn}^{6+} $$
So, according to $\mathrm{pH}$, the reaction and potential of cell changes.
In acidic medium
$$ \mathrm{MnO}_{4}^{-}+5 \mathrm{e}^{-} \longrightarrow \mathrm{Mn}^{2+} $$
In neutral medium
$$ \mathrm{MnO}_{4}^{-}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Mn}^{4+} $$
In basic medium
$$ \mathrm{MnO}_{4}^{-}+\mathrm{e} \longrightarrow \mathrm{Mn}^{6+} $$
So, according to $\mathrm{pH}$, the reaction and potential of cell changes.
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