Reagents for analysis of iron(II)-iron(III) mixtures

and

s.

Sudarshan Lal N. Srivastava Agro College Agra, U.P. India

I

1

Reagentntr for Analysis of hon(ll)-hon(W) Mixtures

Iron(111) salts are usually detected by their characteristic behavior toward IL[F~(CN)B], KCNS, Cupferron, etc., while iron(I1) salts are detected with reagents, viz: a-a' dipyridyl and dimethylglyoxime. We hereby report the use of A few familiar analytical reagents which may be helpful in detection of iron(I1)-iron(II1) mixtures. Sodium cobaltinitn'te. Iron(I1) yields a yellow p r e cipitate with the reagent, while iron(II1) is unaffected. To a few drops of the mixture solution, add sodium cabaltinitrite solution until there is no further precipitation. Warm, centrifuge, and filter in a microcone. Residue responds to tests for iron(II), and the centrifugate yields a blood red coloration with potassium thiocyanate. A m m o n i u m fluoride. It forms a white precipitate with iron(III), but does not yield any precipitate with iron(I1). Iron(II1) is completely precipitated by adding NHIF, and the centrifugate responds to tests for

482 / Journal o f Chemical Education

iron(I1) with reagents viz dimethylglyoxime, and a-cur dipyridyl. The residue acquires a buff color on warming and is used for detection of iron(II1). I-Nttroso-2-naphthol. Alcoholic or aqueous alcoholic solution of the reagent can he employed. Iron(II1) yields a brown color, while iron(I1) gives a green color. The test is best performed as a spot on paper. To one drop of the test solution on a spot paper, a drop of the reagent is added. Iron(I1) gives a green color at the periphery, whereas a dark brown spot due to iron(II1) appears at the center. Iron(II1) produces a deep red color with thiocyanate which is discharged by mercuric chloride. To the mixture solution (2 drops) KCNS (1%) is added, and the red color is discharged on subsequent addition of mercuric chloride (0.1 M). The colorless solution thus obtained can be used for detection of iron(I1) with reagents, i.e., a-a' dipyridyl and &[Fe(CiY)6]. The dimethylglyoxime test is inhibited in presence of mercury salts.