Excess volumes of mixing of 1:1 electrolyte solutions at 308.15 K in aqua-DMF mixed solvent system

Excess volumes of mixing for six possible binary combinations of solutions of NaCl, KCl, NaBr and KBr have been determined at constant ionic strength of 1.000 and 2.000 mol kg− 1 at 308.15 K in water + N,N-dimethylformamide mixed solvent system using a dilatometer. Data were examined using the Friedman model and the mixing parameters related to the pair, triplet, and higher interactions, i.e., v0, v1, and v2 were calculated. Data follow the cross square rule (CSR) at I = 2.000 mol kg− 1 but not at I = 1.000 mol kg− 1. The deviation from CSR is considered to arise from preferential solvation of the ions and ion clusters in the mixed solvent system. It is observed that the higher number of DMF molecules is in the solvation shell of an ion the larger is the deviation from CSR.