Sudarshan Lal
and S. N. Srivastava Agra College Agra, u.P., India
Some Analytical Reagents for Th(N)-Th(W) Mixtures
W e present below a few familiar reagents which may be used for the analysis of tin(I1)-tin(1V) mixtures. Amido black. A 0.1% aqueous solution of the reagent is prepared. Tin(I1) yields a red spot with the reagent on subsequent acidification with HCl, while tin(1V) gives a blue color. To a drop of the unknown solution on a spot paper, add one drop of amido black follo~r-edby a drop of concentrated HCI. Simultaneous appearance of a blue and red color confirms tin(1V) and tin(II), respectively. The intense blue color obtained in presence of tin(IV) is distinct from that of the original color of the reagent (light blue) used in a blank test. Potassium ferrocyanide-ammaium molybdate reagent. To a drop of the mixture solution on a spot paper add 1 drop of 1% potassium ferrocyanide followed by a few drops of ammonium molybdate. Blue spots due to molybdenum blue in presence of tin(I1) appear both a t center and periphery. A reddish-brown color like that of rusting iron confirms the presence of tin(1V). Potassium ferricyanide. Tin(I1) with ammonium molybdate and excess of K8[Fe(CN)s] yields a brown precipitate while tin(1V) is not affected. The test solution is treated with ammonium molybdate-K3[Fe(CN)a] reagent, centrifuged, and filtered. The residue responds to tests of tin(I1) while centrifugate obeys tests for tin(1V). Potassium thiocyanate. Tin(I1) yields only a fine yellowish opalescence and tiu(IV) gives a white precipi-
tate. A few drops of the mixture are boiled with potassium thiocyanate (0.5 M) and, after centrifugation, filtered in a microcone. The centrifugate gives molybdenum blue with ammonium molybdate showing, thereby, the presence of tin(I1). The residue is soluble in concentrated HCl and yields a rusty brown precipitate with Kp[Fe(CN)s]-ammoniummolybdate confirming the presence of tin(1V). Brmnophenol blue. A 2% aqueous solution of the reagent is used. Tiu(1V) yields a yellow precipitate which separates out on warming, whereas tin(I1) gives no precipitate. To two drops of the mixture solution, 2% solution of the reagent until a permanent turbidity appears. Warm, centrifuge, and filter in a microcone. The centrifugate gives positive tests with ammonium molybdate; amido black confirms the presence of tiu(II), while the residue on dissolution in concentrated HC1 with the subsequent addition of K,[Fe(CN)e]ammonium molybdate reagent gives a rusty brown precipitate showing the presence of tin(1V). Indigo carmine. The presence of tin(I1) can be ascertained by ammonium molybdate in the mixture solution. Tin(I1) gives a green color with an aqueous solution of indigo carmine, and tin(1V) yields a greenish precipitate. After ascertaining the presence of tin(I1) in the mixture, add an aqueous solution of indigo carmine and warm. The residue responds to tests for tin(1V).
Volume 44, Number 8, August 1967
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