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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 5, Number 1
February 20, 1961 

Volumetric Determination of a small amount of Iron with Potassium Ferrocyanide

훼로시안화 칼리움에 의한 철의 미량적정법
Chong Hun Won

A titration of a small amount of iron with standard potassium ferrocyanide using potassium thiocyanate as indicator has been studied. A sample solution containing 0.1∼1.0 mg. Fe3+ in 60 ml. is pipeted into 100 ml. Erlenmyer flask and the pH of the solution is adjusted to 1.5∼3.0 with 0.1 N or 1 N HNO3 and NH4OH. To this solution one ml. of 1 M KCNS solution as indicator is added. The solution colored by iron thiocyanate complex is titrated with 1/200 M or 1/400 M standard solution of potassium ferrocyanide from a 5 ml. micro-buret. Near the end point, when the color of sample changes from deep red to green, about 20 ml. of ether is added and shake the flask vigorously. The red color is extracted to the ether layer. To settle the ether layer a few drops of ethanol is added and then standard solution is added dropwise and shake vigorously. The end point is reached when the color of the ether layer disappears owing to the quantitative formation of Fe4[Fe(CN)6]3. In this titration, 0.lmg. of Fe3+ can be determined within 1.0% of titration error, provided the following optimum conditions, i.e., pH 1.5∼3.0, final concentration of KCNS indicator; 0.01∼0.02M, at room temperature. The titration found to be interfered by the presence of slightly soluble salts, stable complex forming ions and the ions which would be reduced by ferrocyanide or oxidized by ferric ion.
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