Standard aqueous potentials for the {thallium amalgam|thallium(I) iodide} electrode, and thermodynamic solubility product of thallium(I) iodide at temperatures from 298.15 K to 328.15 K

The std. potential E°{TlI + e- = Tl(in TlxHg1-x) + I-} of the {thallium-amalgam|thallium(I) iodide} electrode was detd. from electromotive-force measurements of the double cell: Ag|AgI|KI(aq)|TlI|TlxHg1-x|TlCl|KCl(aq)|AgCl|Ag. The results are: E°/V = -(0.72872 ± 0.00021), -(0.73266 ± 0.00010), and -(0.73711 ± 0.00026), at the temps. 298.15, 313.15 and 328.15 K, resp. Therefrom the thermodn. soly. product K°s of aq. thallium(I) iodide was obtained, giving pK°s = 7.354 ± 0.004, 6.729 ± 0.003, and 6.198 ± 0.005, resp., at the 3 temps. mentioned above. Comparing with the analogous literature values for thallium(I) bromide and thallium(I) chloride, a strikingly linear relation between pK°s and the reciprocal of the crystallog. radius of the relevant halide ion emerges, pointing to a dependence of pK°s on the primary hydration nos. of such ions.