Indirect polarographic determination of silicic acid using solvent extraction

Abstract

For the determination of 0.010.2% silicon in steels, a 0.25 g sample was decomposed with 12 ml of (1+6) sulfuric acid and 5 ml of 15% hydrogen peroxide, and then boiled to destroy the excess of the peroxide. After an addition of 5 g of ammonium sulfate, the solution was transfered into a 100 ml volumetric flask, and filled to the mark with water. The pH of the final solution should have been 1.1 ± 0.1. A 20 ml aliquot was transfered into a separatory funnel, and 4 ml of 10% ammonium molybdate solution was added. After 4 minutes' standing, 12 ml of 9 N sulfuric acid was added and the silicomolybdic acid formed was extracted immediately with 10 ml of iso-butanol. The extract washed 4 times with 5 ml of 2 N sulfuric acid was transfered into a 25 ml volumetric flask, and filled up to the mark with 8 ml of ethanol and water. The polarogram was then recorded in the usual way, the double waves of silicomolybdic acid being at -0.3 V and -0.5 V vs. the S. C. E. Germanium(IV) took the same behavior under the condition. The values by this method agreed well with the certificated values of the standard steels.
Another method involving the measurement of the maximum wave produced in a perchloric acid-hydrogen peroxide-iso-butanol mixture, was also investigated for determining minute amounts of silicon and germanium.