Search

The following cell was used to determine the standard free energy of formation of Bi3+ (aq): (-)Pt, H2 HClO4, Bi(ClO4)3 Bi, Hg (sat.) (+) The saturated amalgam contained bismuth at the same chemical potential as the pure metal, but gave a more reproducible and rapidly reversible potential. Measurements were made at various perchloric acid concentrations between 0.6 and 4.0 M which served to repress hydrolysis and provided a constant ionic medium. At each perchloric acid concentration the Nernst equation was obeyed since [Bi3+] was small relative to the total ionic concentration, and thus activity coefficients were constant For 1 M HClO4. E = 0.2921 + RT/3F ln [B3+]/[H+]3 V, 25°C. It was found that the apparent standard electrode potential E′0 varied only slightly as the total ionic concentration C was changed. E′0 = 0.2928–0.00072 C ± 0.0005 V. Hence the standard electrode potential at infinite dilution is E0 = 0.2928 ± 0.0005 V, and the activity coefficient factor fBi3 + /f3H+ is close to unity in 0–4 M HClO4. δG0f, Bi3+(aq) = +20.26 kcal mole-1 and the free energy of hydration, Bi3+(g) → Bi3+(aq), δG0h = —1166 kcal mole-1 Hydration free energies of metallic cations appear to correlate with ionization potentials.