Potentiometric studies on bismuth ferrocyanide and the determination of bismuth

Summary

The reaction between bismuth nitrate and ferrocyanides of alkali metals such as sodium, potassium, lithium and ammonium, has been studied potentiometrically using platinum as an indicator electrode in conjunction with a saturated calomel electrode through KNO₃ bridge. The equivalence point obtained from the maximum value of dE/dV corresponds to the formation and complete precipitation of a compound having molecular formula BiMFe(CN)₆, where M represents an alkali metal. The potentiometric curves are symmetrical on both sides of the end point and the results obtained are very accurate and reproducible. The method of potentiometric titrations, though simple, offers a rapid and accurate means for the determination of bismuth solutions at fairly low concentrations. The effect of addition of ethanol and electrolytes on the course of the reaction has been studied.