Adsorption of sulphur-containing species at the mercury/water interphase

Abstract

The adsorption of SCN^– ions and thiourea has been investigated by measuring the capacity of a mercury electrode. Adsorption isotherms for SCN^– indicate a large ion-ion interaction which appears to decrease as the bulk solution concentration increases. In contrast, thiourea adsorption can be expressed by a Frumkin isotherm with constant interaction parameter equivalent to a second virial coefficient of 84 Ų molecule^–1. The apparent dielectric constant passes through a maximum at a charge on the electrode of about + 6_µC cm^–2. Thiourea displaces adsorbed nitrate ions from the mercury electrode. Inaccuracies in the drop-time method for determining interfacial tension are discussed and a new method for obtaining an approximate value of the absolute mercury-water interfacial tension is described.