At what pH does the potential (EMF) for the disproportionation of chlorine change from a negative value to a positive value, assuming 1.0 bar pressure and 1.0 M concentration for all species except hy

Question

At what pH does the potential (EMF) for the disproportionation of chlorine change from a negative value to a positive value, assuming 1.0 bar pressure and 1.0 M concentration for all species except hydrogen ion? Given: Cl2 + 2e^– -> 2Cl^– ; E° = 1.36 V and 2OCl^– + 4H^+ + 2e^– -> Cl2 + 2H2O; E° = 1.63 V. [2.303RT/F = 0.06]

Prashant Kotian · Accepted Answer

Correct answer: C. The disproportionation reaction is Cl2 + H2O -> Cl^- + OCl^- + 2H^+. E°_cell = 1.36 - 1.63 = -0.27 V. The Nernst equation for this reaction is E = E° - (0.06/2)*log([H^+]^4) = -0.27 + 0.12*pH. Setting E > 0 gives 0.12*pH > 0.27, so pH > 2.25. Therefore, correct answer is C.

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