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Electrochemistry
Electrochemical Series and Feasibility
1 question from 1 paper, each with its answer.
- question
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- paper
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Concepts tested
- Comproportionation of iron
All Questions
2001 AIPMT 1 question
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Standard electrode potentials are $Fe^{2+}/Fe$: $E^\circ = -0.44$ V and $Fe^{3+}/Fe^{2+}$: $E^\circ = 0.77$ V. If $Fe^{2+}$, $Fe^{3+}$ and Fe block are kept together, then :-$Fe^{3+}/Fe^{2+}$ has the higher reduction potential (+0.77 V), so $Fe^{3+}$ is reduced. $Fe^{2+}/Fe$ has the lower potential (–0.44 V), so Fe metal is oxidised.
Reaction: $Fe + 2Fe^{3+} \rightarrow 3Fe^{2+}$
$E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode} = 0.77 - (-0.44) = 1.21$ V, which is positive, so the reaction is spontaneous.
So $Fe^{3+}$ decreases (and $Fe^{2+}$ increases).