Physico-chemical studies on acidity functions in mixed solvents II Studies on the pH of potassium hydroxide solutions in ethanol-, n-propanol-, Iso-propanol- and ethylene glycol water mixtures

ABSTRACT

The slope factors of the lines relating the electromotive force E of the pH-meter cell with the pH reading R agree consistently with the theoretical values for all test solutions at 25 degree. This may be considered as an indication of the proper function of the glass electrode as a standard hydrogen electrode. A discussion is made of the factor governing the glass electrode function such as chemical composition, water content, alkali and acid errors. The validity of Dole 's theory is examined by plotting the voltage deviation E against-log H2O of the solvent mixtures and determining the number of water molecules associated with proton in its migration from the solution into the surface of the electrode glass membrane. Deviation of the experimental points from the fitted least squares -lines proves that the theory is not valid, particularly for solutions of potassium hydroxide in ethylene glycol-water mixtures. Although the availability of the transferable protons is considerably affected by changes of the activity of water, it seems unlikely that the transfer of water through the surface of the galss membrane plays any part in the electrochemical process responsible for the development of the pH response. Calculated values of the operational pHx and liquid-junction potentials Ej are obtained for the different test solutions. Variation of the pHx with solvent composition is explained in terms of solvent-solvent and ion-solvent interactions