Amperometric titration of the weak acids with the use of a tungsten electrode

Abstract

A tungsten electrode gives a well-defined current-voltage curve with good depolarization in pH buffers aerated by carbon dioxide-free air. The mixed potential obtained by the reduction of dissolved oxygen and the oxidation of tungsten electrode is shifted at a rate of about -40 mV/ unit pH.
Accordingly, an amperometric titration of weak acid by the standard barium hydroxide solution is made by setting the tungsten electrode potential on an expected mixed potential at pH of the end point previously calculated out. Titration of 0.1N and 0.01N weak acids, such as acetic acid, benzoic acid, formic acid, sodium hydrogen phthalate, ο-nitrophenol, maleic acid, oxalic acid, malic acid, succinic acid and salicylic acid, gave satisfactory results with coefficient of variance less than 0.9% better than those of pH titration with glass electrode. It was noticed that the first equivalence point of maleic acid was obtained by this titration while it was difficult to be determined by the conventional pH titration. The presence of an oxidant disturbs the titration.