Date of Award


Degree Type


Degree Name

Master of Science in Oceanography



First Advisor

M. Pilson


The object of this study was the determination of the first, second and third apparent dissociation constants for arsenic acid in seawater, based on a free molal hydrogen scale. This was accomplished through potentiometric monitoring of acid-base titrations of arsenate in artificial seawater and data analysis using a computerized curve fitting technique. Experiments were carried out at atmospheric pressure over a range of salinities and temperatures. Constants determined in artificial seawater and sodium chloride solutions at equal effective ionic strengths were compared in order to evaluate the effects of specific ion interactions on the dissociation of arsenic acid in seawater. The results suggest that about 25% of the reactive arsenate in seawater is ion paired with cations other than sodium. A comparison of arsenic acid with its analogue, phosphoric acid, revealed the latter as the more dissociated under typical seawater conditions. 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.



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