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Vol.11, No.1, 46 ~ 52, 1973

Title

Acidimetric Determination of Tungsten ( Part 2 )

이원해 Won Hae Lee

Abstract

The neutralization of wolframate ion, WO₄^=, was studied in the presence of neutral salt. The equilibrium was established quickly for the region smaller than 1.15 of average number of H^+ bound per WO₄^=(Z). For the region of Z>1.15 the potential was found to drift slowly for long time without reaching a stationary value. At the region of Z=1.15 the potential drifted rapidly for tire first one minute after each addition of the acid, and then the rate of the drift was only 0.01 to 0.02 pH unit per minute. The neutralization curve of wolframate shows large potential break in the presence of neutral salt. The inflection point of neutralization curve appears at the point of Z=1.148±0.001 when the potentials were measured two to three minutes later after each addition of acid at the region of slow reaction. Only one or two potential measurements are enough to locate the inflection point at slow reaction range since the inflection point lies at the neighbour of starting point of slow reaction. In the presence of enough neutral salt the potential break was so large that such small changes of potential did not affect the accuracy of the titration. Also the influences of molybdate and carbonate have been studied. Analytical procedure was described for the determination of tungsten in the synthetic mixtures.

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