Determination of chromate and cyanide by anion-exchange with lead iodate, and the analysis of mixtures of cyanide, thiocyanate and halides.
Chromate and cyanide have been determined by their ability to displace iodate from sparingly soluble lead iodate. The released iodate is treated with acidified iodide to give iodine, which is determined either by titration with thiosulphate, or spectrophotometrically as its blue complex with starch. Chromium(III) has been determined as chromate after its oxidation with peroxydisulphate. Sulphate, iodide, bromide, chloride, fluoride, oxalate, tartrate, phosphate and thiocyanate do not interfere. Thiosulphate, sulphite, sulphide, hexacyanoferrate(II) and molybdate ions vitiate the results. Silver, mercury, barium and iron(III) should be masked. Mixtures of cyanide, thiocyanate and halides have been analysed by using complementary procedures that employ the iodates of lead and mercury, and bromine oxidimetry. It has been shown that cyanide or thiocyanate interferes in the determination of iodide by oxidation to iodic acid, because of formation of cyanogen bromide.
Verma
K K
KK
Department of Chemistry, Rani Durgavati University, Jabalpur 482 001, India.
Tyagi
P
P
Ekka
M G
MG