The rate of reduction of selenium(VI) to selenium(IV) in hydrochloric acid.

The reduction of selenium(VI) to selenium(IV) in 4, 5 and 6M hydrochloric acid was studied at temperatures between 50 and 95 degrees . The reaction rate was determined by measurement of the selenium(IV) formed, by continuous-flow hydride-generation atomic-absorption spectrometry. The most notable feature of the reaction is the strong increase in rate with increasing hydrogen-ion concentration and temperature. The rate increases initially with chloride concentration at constant acidity (mixtures of hydrochloric and perchloric acid) but levels off to an almost constant value at high chloride concentrations.