LECLANCHE CELL INVESTIGATIONS .1. ZN(NH3)(2)CL-2 SOLUBILITY AND THE FORMATION OF ZNCL2-CENTER-DOT-4ZN(OH)(2)CENTER-DOT-H2O

The solubility of Zn(NH3)(2)Cl-2 in aqueous solutions containing ZnCl2 and NH4Cl at 298.15 K has been determined by pH titration with ZnO. I n addition, the curve defining the critical concentrations of free ZnC l2 and free NH4Cl which are in equilibrium at 298.15 K in aqueous solu tion with precipitates of both Zn(NH3)(2)Cl-2 and ZnCl2 . 4Zn(OH)(2) . H2O has been determined for the first time by a new method involving potentiometric titrations using ZnO as titrant and zinc electrode pote ntial as indicator. The new information has allowed the overall reacti ons which take place in three or four sequential stages during the dis charge of a traditional Leclanche cell to be reviewed and significantl y modified. The Gibbs free energies of formation of Zn(NH3)(2)Cl-2 and ZnCl2 . 4Zn(OH)(2) . H2O at 298.15 K have been estimated respectively as -505,375 and -2,896,060 J mol(-1). (C) 1997 Elsevier Science Ltd.