Experimental determination and prediction of activity coefficients of RbCl in aqueous (RbCl + RbNO3) mixture at T = 298.15 K

Activity coefficients for rubidium chloride in the (RbCl + RbNO3 + H2O) ternary system were determined from electromotive force (emf) measurements of the cell:Rb-ionselectiveelectrode(ISE)|RbCl(mA),RbNO3(mB),H2O|Ag|AgClat T = 298.15 K and over total ionic strengths from (0.01 upto 3.50) mol · kg−1. The Rb+ ion selective electrode (Rb-ISE) and Ag|AgCl electrode used in this work were made in our laboratory and had reasonably good Nernst responses, which demonstrate that the emf method can be applied to measure the above system with high precision. The experimental data were analyzed using the Harned rule and Pitzer model. The Harned coefficients and the Pitzer binary and ternary ionic interaction parameters for the system have been evaluated. The experimental results obey the Harned rule, and the Pitzer model can be used to describe this aqueous system satisfactorily. The activity coefficients of RbNO3, the osmotic coefficients of the mixtures and the excess free energy of mixing were also calculated.