Simultaneous Determination of Selenious Acid and Alkali Halide in Their Mixture by Short-circuit Argentometric Amperometric Titration

Abstract

The argentometric titration of selenious acid by the short-circuit amperometric technique using a rotating platinum wire electrode (1000 rpm) vs. SCE, and the differential determination of alkali halide and selenious acid have been studied.
Selenious acid (0.00005-0.01 N) can be directly titrated with silver nitrate after adjusting the pH to 9.5-12.5 with sodium hydroxide. The precise determination is testified at the concentration range of 0.001-0.01 N; either the relative error or the coefficient of variation. being about 0.2%. The whole procedure requires only 5 minutes. The presence of sodium selenate does not interfere determination, but ammonium salts give serious interference.
A recommended procedure for the simultaneous titration of alkali halide and selenious acid. is as follows.
Triton X-405 is added to the aqueous solution of a mixture of selenious acid and one of alkali halide (potassium iodide, potassium bromide or potassium chloride) in a titration cell. The solution is diluted to 100 ml so that the final concentrations are 0.0005-4/ 001 N in selenious acid, 0.0005-M.001 N in alkali halide, and 0.O2 w/v % in Triton X-405. After the solution is titrated with O.1 N silver nitrate standard solution to the end point of alkali halide, sodium hydroxide is added to the same solution in order to make the pH about 10, and then titration is continued to the end point of selenious acid. The relative errors are about 0.2% for O.001 N potassium iodide and selenious acid, respectively. The whole procedure can be performed in 10 minutes.