Standard Potentials in Water for the Potassium Amalgam Electrode from 283.15 to 343.15 K and for the Potassium Electrode at 298.15 K, and Thermodynamic Functions for Dilute Potassium Amalgams and for Aqueous Potassium Chloride

The standard potentials of the potassium amalgam electrode have been determined from e.m.f. measurements of the reversible cell: Pt|xK+(1+-x)Hg|KCl(aq,m)|AgCl|Ag|Pt, over the temperature range 283.15 to 343.15 K. The results can be represented accurately by the equation: E° V = -1.053755 - 4.561286 × 10-3( T K+4.927894×10-6( T K)2 Combining Eo at 298.15 K with the reversible e.m.f. of the potassium concentration cell: Pt|K|K| in ethylamine|xK+(1 - x)Hg|Pt, which is available in the literature, the standard potential at 298.15 K of the potassium electrode has been redetermined as -2.9284 V. The standard thermodynamic functions at 298.15 K for the potassium amalgam and for the potassium amalgamation reaction have also been obtained. In addition, the mean molar activity coefficients of aqueous KCl have been determined at molalities up to 0.5 mol kg-1 over the temperature range 283.15 to 343.15 K. The logarithm of the rational activity coefficient of potassium in dilute amalgams is a linear function of the mole fraction of potassium: log10fK = Qx, where Q is in turn a linear function of temperature: Q = 61.1122-0.103734( T K).