Thermodynamic studies of some electrolytes in formamide.

The work presented in this thesis constitutes a thermodynamic study of the behaviour of the electrolytes CdCl2, HCl, HBr and CdBr2 in formamide by means of e.m.f., solubility and calorimetric measurements. The e.m.f. of cells, (1) Cd/CdCl2(s)/Cl-/AgCl-Ag, and (2) Cd-Hg/CdCl2(s)/Cl-/AgCl-Ag where CdCl2(s) is a solid solvate with formamide, have been measured using HCl and KCl solutions in formamide at various chloride concentrations, at 5, 10,15, 20, 25 and 30°C. The standard potential of the Cd/CdCl2(s) electrode in formamide has thus been evaluated at these temperatures. The thermodynamic quantities, ? G° and ? H° for the interaction of anhydrous cadmium chloride with formamide to form the solid solvate have been calculated. The heat of this interaction has been measured calorimetrically and is in excellent agreement with the calculated from the temperature dependence of e.m.f. data. The composition of the complex has been established by thermo-gravimetric analyses to be CdCl2.21/2 HCONH2. The solubility of CdCl2 in NaCl solutions in formamide has been measured, using a radio-chemical technique at various chloride concentrations and temperatures. At 25°C, the solubility of CdCl2 in pure formamide is 0.022 g moles Kg-1. Measurements of the e.m.f. of the cell, Cd-Hg/CdCl2(m)/AgCl-Ag, where m is the molality of the CdCl2 in unsaturated solutions in formamide, have also been made at 25°C, with the object of determining the standard potential of the cadmium electrode in formamide. The cells, (1) Pt, H2 / HCl (m) in formamide/ AgCl-Ag, and (2) Pt, H2 / HBr (m) in formamide/ AgBr-Ag, have been examined at 5, 15 and 25°C. The standard potential of AgCl-Ag and AgBr-Ag electrodes have been evaluated at these temperatures. The results for the cell Pt, H2/ HCl (m) in formamide / AgCl-Ag at 25°C are in good agreement with a recent literature value. The activity coefficients of HCl and HBr in this solvent have been calculated. Measurements on the cell Pt, H2/HCl (m) in formamide/AgCl-Ag were combined with the solubility products of AgCl in formamide, measured at 15 and 25°C by Dhabanandana1 and the standard potential of the silver electrode E°Ag was calculated at these temperatures. Measurements on the cell Pt, H2 / HBr (m) in formamide/AgBr-Ag together with the above E°Ag values have then been used to calculate the solubility products for AgBr in formamide at 15 and 25°C, The heat of precipitation of AgBr in formamide has been measured calorimetrically and is in good agreement with the value calculated from the temperature dependence of the solubility product. The cells, (1) Cd/CdBr (s)/Br-/AgBr-Ag and (2) Cd-Hg/CdBr(s) /Br-/AgBr-Ag have also been studied at 5,15 and 25°C. The e.m.f.'s of these cells were combined with the standard potential of AgBr-Ag electrode at these temperatures to evaluate the standard potential of the Cd-CdBr2 electrode.