COMPUTER CALCULATION OF LIQUID-JUNCTION POTENTIALS .3. TEMPERATURE-DEPENDENCE OF JUNCTION POTENTIALS

Junction potentials for KCl(4M) parallel-to X where X is one of NaCl, LiCl, NaOH, HCl, Li2SO4, Mg(NO3)2, LaCl3 ranging in concentration from 0.001 to 4 M have been calculated at 0, 25, 100-degrees-C by using the simulation and numerical methods of Parts I and II [J. Bagg, Electrochim. Acta 35, 361, 367 (1990)]. Junction potentials ranged from -36.2 mV (4 M HCl, 0-degrees-C) to 26.1 mV (NaOH 4 M, 25-degrees-C) and their average temperature coefficients ranged from -0.16 (0.001 M NaCl) to 0.05 (4 M LiCl) mV C-1. The variation of junction potentials with temperature can lead to large liquid junction errors in those pIon determinations where standardization and measurement are carried out at markedly different temperatures. For example, the pH of hot water may have to be determined when monitoring cooling systems in the electrical generation industry. In such a determination if a glass electrode standardized in an NBS buffer (Na2CO2/NaHCO3) at 25-degrees-C was used to measure pH of water at 100-degrees-C then this pH would be subject to a liquid junction error of DELTA-pH = 0.38. If the water was cooled to 25-degrees-C before pH measurement then the junction error would be DELTA-pH = 0.14.