The potential/pH diagram of silver in aqueous ammonium salt solution

Abstract

The potential/pH diagram of silver in aqueous ammonium salt solution at 25°C has been calculated and verified experimentally.

Calculations were carried out on the basis of the standard potential of the silver/silver-ion couple, the dissociation constants of the silver mono- and di-ammonia complex, and the dissociation constant of the ammonium ion, the total silver and nitrogen content being kept constant. The calculated diagram was verified by measuring the potential of the silver electrode at pH values varying from 2 to 12.

The measured diagram agrees well with the calculated one; minor differences (up to 15 mV) occur only in the alkaline range.

The establishment of the potential is sufficiently rapid to record the entire diagram on a suitable pen-and-ink X/Y recorder within a few minutes. Accordingly, such a recording may serve well as a lecture demonstration on potential/pH diagrams.