The apparent dissociation constants for arsenic acid in seawater, based on a free molal hydrogen scale, were determined in artificial seawater over a range of salinities and temperatures. A comparison between constants determined in a sodium chloride solution and artificial seawater of the same ionic strength suggests that a significant amount of the reactive arsenate in seawater is ion paired with cations other than sodium. Under typical seawater conditions, arsenic acid appears to be less dissociated than its analogue, phosphoric acid. A series of conversion factors was determined so that these constants could also be applied in conjunction with pH measurements in seawater based on the NBS activity scale
