Spectrophotometric investigations in aqueous solution at elevated temperatures. The effect of temperature on the ionisation constant of the 2,2′ bipyridyl cation

Abstract

The ionisation constant, K_a, of the 2,2′ bipyridyl cation has been determined at various temperatures between 298 and 473 K from spectrophotometric data. The results, expressed as a function of absolute temperature, are given by the equation pK_a=(968.58/T)+ 0.735 53 + 0.001 131 1 T. The increase in ionisation with increasing temperature is attributed to increasing solvation of the hydronium ion relative to the 2,2′ bipyridyl cation.

The changes of enthalpy, entropy and heat capacity for the ionisation reaction have been calculated from the temperature coefficients of the ionisation constant at each of the experimental temperatures.