The net formation constant for tetrachloromercurate(II) ion is 1.2 × 10¹⁵.Calculate the approximate standard electrode potential for:
[HgCl₄]^2-(aq) + 2 e^- → Hg(l) + 4 Cl^-(aq)
Given: Hg²⁺(aq) + 2 e^- → Hg(l) E° + 0.85 V

Question

Quizplus · Accepted Answer

The standard electrode potential for the given reaction can be calculated using the Nernst equation and the given formation constant. The formation constant (Kf) for [HgCl4]^2- is 1.2 × 10^15. This high value indicates a strong tendency to form the complex ion, which affects the electrode potential. The given standard electrode potential for the reduction of Hg^2+ to Hg(l) is +0.85 V. The formation of the complex ion from Hg^2+ involves the binding of 4 Cl^- ions, which shifts the equilibrium and affects the potential. The calculation involves thermodynamic relationships, including the Nernst equation and the relationship between the formation constant and the Gibbs free energy change (ΔG° = -RT ln Kf), which ultimately affects the electrode potential. The exact calculation requires detailed thermodynamic data, but the provided information and the high formation constant suggest an adjustment to the standard potential, leading to the correct answer of +0.41 V, indicating a less positive potential than for the reduction of Hg^2+ alone due to the formation of the complex ion.

The Net Formation Constant for Tetrachloromercurate(II)ion Is 1