CBSE 2025, Set 3

Question

For a galvanic cell, the following half reactions are given. Decide, which will remain as reduction reaction and which will be reversed to become an oxidation reaction. Give reason for your answer.

(I) Cr$^{3+}$ + 3e$^-$ → Cr(s);  E° = −0.74 V

(II) Fe$^{2+}$ + 2e$^-$ → Fe(s);  E° = −0.44 V

Edvaya · Accepted Answer

The correct answer is Subjective. In a galvanic cell, the half reaction with the **more positive (or less negative) reduction potential** occurs as **reduction at the cathode**, and the other is **reversed to become oxidation at the anode**. Comparing the two reduction potentials: - Reaction (I): E° = −0.74 V (more negative) - Reaction (II): E° = −0.44 V (less negative) **Reaction (II) will remain as reduction reaction (cathode):** $$	ext{Fe}^{2+} + 2e^- ightarrow 	ext{Fe(s)}$$ **Reaction (I) will be reversed to become oxidation reaction (anode):** $$	ext{Cr(s)} ightarrow 	ext{Cr}^{3+} + 3e^-$$ **Reason:** Chromium has a **lower (more negative) electrode potential** than iron. A lower reduction potential means greater tendency to be oxidised (stronger reducing agent). Therefore Cr acts as the anode (undergoes oxidation) and Fe$^{2+}$ acts at the cathode (undergoes reduction).

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