Int J Thermophys (2016) 37:83 DOI 10.1007/s10765-016-2088-3 Measurement and Modeling of Mean Activity Coefficients of NaCl in an Aqueous Mixed Electrolyte Solution Containing Glycine Paniz Sheikholeslami 1 · M. R. Dehghani 1 · Tina Safahieh 1 Received: 11 January 2011 / Accepted: 11 June 2016 / Published online: 27 June 2016 © Springer Science+Business Media New York 2016 Abstract An electrochemical cell with two ion-selective electrodes (Na + glass) and (Cl − solid state) was used to measure the mean ionic activity coefficient of NaCl in an aqueous mixture containing NaCl, glycine, and NaNO 3 at 308.15 K. The experiments were conducted at fixed molality of NaNO 3 (0.1 m) and various molalities of glycine (0–1 m) and NaCl (up to 0.8 m). The experimental data were modeled using a modified version of the Pitzer equation. Finally the activity coefficient ratio of glycine was determined based on the Maxwell equation. Keywords Activity coefficient · Amino acids · Ion-selective electrodes · Mixed electrolyte solutions · Modified Pitzer equation Nomenclature E I Potential difference in the presence of NaCl E II Potential difference in the presence of NaCl and glycine E III Potential difference in the presence of NaCl, glycine, and NaNO 3 E o Standard potential difference of the cell S Nernstian slope m Concentration in molality m A Molality of amino acid m B Molality of NaCl m C Molality of NaNO 3 B M. R. Dehghani m_dehghani@iust.ac.ir 1 School of Chemical Engineering, Iran University of Science and Technology, Tehran, Iran 123