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NEET CHEMISTRYMedium

If EFe2+/Fe=0.441 VE^\circ_{\text{Fe}^{2+}/\text{Fe}} = -0.441 \text{ V} and EFe3+/Fe2+=0.771 VE^\circ_{\text{Fe}^{3+}/\text{Fe}^{2+}} = 0.771 \text{ V}, the standard emf of the reaction: Fe+2Fe3+3Fe2+\text{Fe} + 2\text{Fe}^{3+} \rightarrow 3\text{Fe}^{2+} will be:

A

0.330 V

B

1.653 V

C

1.212 V

D

0.111 V

Step-by-Step Solution

The overall cell reaction is given as: Fe+2Fe3+3Fe2+\text{Fe} + 2\text{Fe}^{3+} \rightarrow 3\text{Fe}^{2+}.

This reaction can be split into two half-reactions:

  1. Oxidation at Anode: FeFe2++2e\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^- (Standard reduction potential, Eanode=EFe2+/Fe=0.441 VE^\circ_{\text{anode}} = E^\circ_{\text{Fe}^{2+}/\text{Fe}} = -0.441 \text{ V})
  2. Reduction at Cathode: 2Fe3++2e2Fe2+2\text{Fe}^{3+} + 2e^- \rightarrow 2\text{Fe}^{2+} (Standard reduction potential, Ecathode=EFe3+/Fe2+=0.771 VE^\circ_{\text{cathode}} = E^\circ_{\text{Fe}^{3+}/\text{Fe}^{2+}} = 0.771 \text{ V})

The standard emf of the cell (EcellE^\circ_{\text{cell}}) is calculated using the formula: Ecell=EcathodeEanodeE^\circ_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}} Ecell=0.771 V(0.441 V)E^\circ_{\text{cell}} = 0.771 \text{ V} - (-0.441 \text{ V}) Ecell=0.771 V+0.441 V=1.212 VE^\circ_{\text{cell}} = 0.771 \text{ V} + 0.441 \text{ V} = 1.212 \text{ V}

Note: Standard electrode potential is an intensive property . Therefore, multiplying the stoichiometric coefficients of the reduction half-reaction by 2 to balance the electrons does not change the value of its EE^\circ.

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