Standard electrode potentials are Fe²⁺/Fe: E°= -0.44 V and Fe³⁺/Fe²⁺: E°= 0.77… | Electrochemical Series and Feasibility

Looking for classes? Ksquare Career Institute, Bengaluru →

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 :-

A $Fe^{3+}$ increases

B $Fe^{3+}$ decreases

C $\dfrac{Fe^{2+}}{Fe^{3+}}$ remains unchanged

D $Fe^{2+}$ decreases

The answer is B.

Solution

$Fe^{3+}/Fe^{2+}$ 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).

Concept Comproportionation of iron

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 :-

Solution

Electrochemistry in past papers

Practice

Free resources

Platform

At the institute