| Abstract: | The solubility-product constant of LaF,(s) was obtained by potentiometric titration of sodium fluoride with lanthanum perchlorate in sodium perchlorate solutions of various ionic strengths. The limiting value of pKs.p were found to be 17.65 and 17.95 at 20° and 25°C, respectively. Thermodynamic calculation from these values gives δG° =-102.46 kJ mol?1, δH° = 100.40 kJ mol?1 and δS° = 680.40 JK?1 for the reaction, La+3 (aq)+3F-(aq)=LaF,(s), and δG° =-1613.8kJ mol-1, δH1° =-1594.0kJ mol?1 and S° =433.1 J K?1 mol?1 for the formation of LaF2,(s) at 25°C. The mean activity coefficients and solubilities of LaF2,(s) in NaCIO4 solution at various ionic strengths at 25°C were evaluated. |
