Mean ionic activity coefficient ratio of NaBr and DL-valine in the (water + DL-valine + NaBr + K3PO4) system at T = (298.2 and 303.2) K

• Ion selective electrodes are used in activity coefficient measurements.
• Mean ionic activity coefficient ratios of NaBr and DL-valine are evaluated.
• The system of DL-valine and two electrolytes has been studied.

The mean ionic activity coefficient of NaBr in the (water + DL-valine + NaBr + K3PO4) system was determined by potentiometry at T = (298.2 and 303.2) K by using two ion-selective electrodes, (Na+) against (Br−). The maximum concentrations of sodium bromide, potassium phosphate, and DL-valine were (1.0, 0.01, and 0.4) mol · kg−1, respectively. The activity coefficient of DL-valine was evaluated from mean ionic activity coefficients of NaBr by using a cross-differential thermodynamic relation.