An Equation for the Activity Coefficient of the Ions of Strong Electrolytes for Concentrations up to 0.1 N

University College of Science, 92, Acharya. Prafulla. Chandra Road, Calcutta.-700 009 Manuscript received 7 November 1979, accepted 18 March 1980 It has been shown that the Debye Hϋckel equation for the activity coefficient of the ions of strong electrolytes requires modification. The modification consists in replacing (\(\Sigma n\))\( {1 \over 2}\) in the expression for Kappa by \((\Sigma n)\) \({1 \over 3}\) / (2πa)\({1 \over 2}\) where a = [(a+)(a_)]\({1 \over 2}\) and a_ re­presenting the "effective diameter" of the positive and negative ions of a symmetrical electrolyte and \(\Sigma\)n the sum of the number of positive and negative ions per cc of the solution. The volume of the composite cell in the phase space containing a pair of oppositely charged ions has been defined. The modified, equation has been subjected to test using the data available in the literature on HCl, NaCI, KCl and CuSO4 and ZnSO4 and has been found satisfactory