Activity coefficients of HCl in HCL+GaCl3+H2O at 5 different temperatures from 278.15 to 318.15K have been determined at total ionic strengths from 0.4 to 1.5mol/kg using a cell of the type: Pt|H2(101.325kPa)|HCl(mA),GaCl3(mB),H2O|AgCl|Ag (A) The results for the 150 experimental emf data points have been used to determine the variation of the activity coefficients of HCl with the change in molality of GaCl3 in the solution. It is found that the linear form of Harned's rule is obeyed for HCl. Besides the ion-interaction model (Pitzer's electrolyte solution theory) has been applied to this system, the Pitzer's parameters of GaCl3:(β^(0)Ga,Cl+θGa,H),β^(1)Ga,Cl,CGa, Cl, ΨGa,H,Cl were obtained by the method of least squares. According to Yang and Pitzer, the mixing parametes,θ Ga,H and β^(O)Ga,Cl are obtained in terms of Harned coefficient of HCl,αA,from the value of (β^(0)Ga,Cl+ θGa,H). The activity coefficients of GaCl3 in the system are calculated using Pizter equation. It is found that the extensive Harned equation is obeyed for GaCl3.

Key words: METAL COMPOUNDS, HYDROCHLORIC ACID, GALLIUM CHLORIDE, WATER, ACTIVITY COEFFICIENT