 Solution

ID: past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2021/paper-1/4/d/ii/solution

(0.1)^{4} (0.3) / (3 \times 1 0^{- 6}) = 10

. Hence

Q = 101 0^{11 pH}, E = 1.945 - \frac{RT l n 10}{4 F} (1 + 11 pH) .

Using the supplied constants at

298 K

E ≃ 1.9302 - 0.1626 pH V .

At pH 7, $E ≃ 0.792 V$ . This is the formal fixed-thermodynamic activity calculation requested; actual cerium speciation and thermodynamic activities would need to remain compatible with the chosen pH to realize it experimentally.

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