The electric conductance of simple molten electrolytes

Abstract

Measurements of electric conductance as a function of temperature have been made for the pure liquids: MgCl 2 , MgBr 2 , Mgl 2 , CaCl 2 , CaBr 2 , Cal 2 , SrCl 2 , SrBr 2 , Srl 2 , BaCl 2 , BaBr 2 , Bal 2 , ZnCl 2 , ZnBr 2 , Znl 2 , CdCl 2 , CdBr 2 , Cdl 2 , HgCl 2 , HgBr 2 , and Hgl 2 , from the melting-point to a maximum temperature of 1100°C, and with an accuracy of 0.2 to 0.3%. Novel preparations have resulted in liquids free from oxy-halides. The energy of activation (∆ H 0↕ expt. ) for conductance is constant with temperature for the halides of group II A, except for that of beryllium chloride, and for certain cadmium and mercuric halides. For beryllium chloride and zinc halides, it varies markedly with temperature. For group II A halides, ∆ H 0↕ expt. increases with r cation , but depends little on r anion . A small increase in equivalent conductance (A) for this group at corresponding temperatures occurs with increase of r cation . It decreases with increase of r anion . For group II B halides, significant trends with r ion are absent. A cell model is not consistent with the magnitudes of ∆ H 0↕ expt . An expression for A is developed on the basis of a hole model. It yields concordance with data for group I A halides on the assumption of a model: M + + X - ⇌ holes. An analogous model for group II liquids is highly discrepant with the data reported. Reasonable agreement of this with a model: M X + + X - ⇌ holes is achieved for group II A halides, except beryllium chloride. Comparison of activation energies for viscous flow and conductance, and transport number data, supports the latter model. The behaviour of beryllium chloride is consistent with a model: (BeCl 2 ) n ⇌ ions ⇌ holes, the equilibrium being to the left at low temperatures. For the molten cadmium halides the results are substantially consistent with the model suggested for group II A halides, with an indication of a small degree of polymerization. Molten zinc halides resemble beryllium chloride in structural type. The conductance of mercuric chloride and bromide is consistent with a model: (Hg X 2 ) ⇌ ions ⇌ holes, the equilibrium being to the left at all measured temperatures.