Precise coulometric determination of acids in cells without liquid junction. Part II. The silver-silver bromide auxiliary anodic reaction

Abstract

The solubilities of silver halides in solutions of their respective halides have been examined. The anodic deposition of silver bromide on silver electrodes has been studied, and mass-transfer limited current densities determined. The resistance of silver bromide films has been investigated, and the critical thickness at which the resistance suddenly rises was found to be inversely proportional to current density. The thickness of films in terms of coulombs per square centimetre and of micrometres was determined, and the specific resistance of various films measured. The magnitude of the “silver error” arising from solubility of silver bromide in bromide solutions and anodic stripping of silver ions to form a precipitate in the bulk of the solution has been established and found to be unacceptably high for precise work, although it can be reduced to less than 0·01 per cent. for less critical work. The behaviour of anodically deposited silver bromide films is explained on the basis of a porous deposit that becomes non-porous at the critical thickness. Conditions are chosen for determinations of 0·05 mol of a monobasic acid at high total currents that are well within the capacity of the silver anode.