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Chemistry Question 56 – JEE-MAIN 2025

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The standard cell potential (Ecell∘) of a fuel cell based on the oxidation of methanol in air that has been used to power television relay station is measured as 1.21 V. The standard half cell reduction potential for O2 (EO2/H2O∘) is 1.229 V. Choose the correct statement:

Understand the roles of anode and cathode in a fuel cell, specifically which species are oxidized and reduced.

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Ninja Strategy•Understand Fuel Cell Fundamentals

Knowing the basic principles of fuel cell operation (continuous reactant supply, oxidation at anode, reduction at cathode) allows for quick elimination of options 1, 2, and 4, leaving option 3 as the only plausible answer, which can then be verified by calculation.

Step 1: Identify Anode and Cathode Reactions and Potentials✦ Active

In a fuel cell based on methanol oxidation and oxygen reduction, methanol is oxidized at the anode and oxygen is reduced at the cathode.

\text{Cathode (Reduction): } \text{O}_2(g) + 4\text{H}^+(aq) + 4e^- \rightarrow 2\text{H}_2\text{O}(l) E^\circ_{\text{cathode}} = E^\circ_{\text{O}_2/\text{H}_2\text{O}} = 1.229 \text{ V} \text{Anode (Oxidation): } \text{CH}_3\text{OH}(l) + \text{H}_2\text{O}(l) \rightarrow \text{CO}_2(g) + 6\text{H}^+(aq) + 6e^- The standard reduction potential for this half-reaction is ECO2/CH3OH∘.
Step 2: Apply the Standard Cell Potential Formula○ Expand

The standard cell potential is given by Ecell∘=Ecathode∘−Eanode∘. Substituting the known values:

1.21 \text{ V} = 1.229 \text{ V} - E^\circ_{\text{CO}_2/\text{CH}_3\text{OH}}
Step 3: Calculate the Unknown Reduction Potential and Evaluate Options○ Expand

Rearranging the equation: ECO2/CH3OH∘=1.229 V−1.21 V=0.019 V. Converting to millivolts: 0.019 V=19 mV. Comparing this result with the options, statement 3 is correct. Statements 1, 2, and 4 are incorrect based on the principles of fuel cell operation.

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