Question
What is standard cell potential for the reaction
$ 3 Ni _{( s )}+2 Al ^{3+}(1 M ) \rightarrow 3 Nl ^{2+}(1 M )+2 Al _{( s )}$
$\text { if } E _{ Ni }^0=-0.25 V \text { and } E _{ Al }^0=-1.66 V ? $

Answer

Given: $E _{ Ni ^{2-} / Ni }=-0.25 V$
$E _{ Al ^{3+} / Al }=-1.66 V ; E _{\text {cell }}^0=?$
Since $Ni$ is oxidised and $Al ^{3+}$ is reduced,
$ E_{\text {cell }}^0=E_{ Al ^{3+} / Al }^0-E_{ Ni ^{2+} / Ni }^0$
$=-1.66-(-0.25)$
$=-1.41\ V $
Ans. $E_{\text {cell }}^0=-1.41\ V$
[Note : Since $E_{\text {cell }}^0$ is negative, the given reaction is not possible but reverse reaction is possible.]

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