Determination of thermodynamic properties of the ternary electrolyte system {CoCl2 + Co(NO3)2 + H2O} by the potentiometric method at T = 298.15

In this work, the Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system {CoCl2 + Co(NO3)2 + H2O}. The activity coefficients were determined using a potentiometric method. The galvanic cell used had no liquid junction of type: Co2+-ISE|CoCl2 (mA), Co(NO3)2 (mB), H2O|Ag.AgCl. The measurements were performed at T = 298.15 K and at total ionic strengths from 0.001 to 6.000 mol · kg−1 for different series of salt ratios r = mCoCl2mCo(NO3)2 = 1.00, 2.50, 5.00, 7.50, 10.00 and 15.00. The PVC based cobalt ion-selective electrode (Co2+-ISE), the PVC based nitrate ion-selective electrode (NO3−-ISE) and the Ag/AgCl electrode used in this work were prepared in our laboratory and showed a reasonably good Nernst response. The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this ternary system.

► The main aim of this work was to get relatively accurate thermodynamic data.
► This paper is a continuation of the research on ternary electrolyte solutions.
► The experimental results obeyed the Harned rule.
► The Pitzer model could be used to describe this ternary system satisfactorily.
► Thermodynamic parameters of the system were determined based on Pitzer model.