Individual activity of calcium ions in pure solutions of CaCl2 and in mixtures.

Individual ion activities were calculated for Ca(2+) in pure solutions of CaCl(2) and in mixtures of CaCl(2) with MgCl(2) and with NaCl, using different conventions to obtain gamma(Ca2+). The results were compared with potentiometric measurements, using calcium specific electrodes. It is found that significant differences should be obtained for emf's using the different conventions, when ionic strength is greater than 0.5. The experimental results obtained for ionic strengths up to 0.2 favor slightly the direct use of gamma(+/-CaCl2), but are fairly consistent also with the use of the Guggenheim and the MacInnes conventions.