N. S. Poonia and W. V. Bhogwat Vikrom Universitv Uiiain, India
II
Qualitative Analysis without Removing Phosphate
A scheme for analysis of groups 111, IV, and V, carried out below pH 7.0, which does not necessitate removing phosphate, is described.' The H2S from the group I1 filtrate is boiled off and treated with 0.5 ml of conc. HNOI. Ammonium chloride and then ammonia is added until there is slight turbidity which can be dissolved in very dilute HC1. For about 30 ml of the solution, about 2 ml of glacial acetic acid and 2 gm of ammonium acetate are added. If a phosphate precipitate of the iron subgroup appears, then 1 rnl of 1 N NarPOa is added t o help the complete removal of the iron subgroup. The precipitate is digested for a few minutes, filtered, washed, and analyzed for the subgroup. Manganese and zinc invariably come down with this precipitate in detectable quantities; and the former, in particular, is tested for a t this stage. VOGEL, A. I., "A Text Book of Macro and Semimicro Quslitative Analysis," Longmans, 1962, p. 450.
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Journal of Chemical Education
When the group precipitate is treated with sodium peroxide, the zincate in the filtrate does not interfere with the aluminum test because the former, unlike aluminate, does not regenerate Zn(OH)* when boiled with NHC1. The filtrate containing the excess of phosphate is treated with 1gm of solid NH4C1,and the warm solution is saturated with HzS. The sulfide precipitate is analyzed as usual for group IIIB. If removal of manganese is incomplete it will interfere only with the magnesium test (see below). The HIS in the filtrate is boiled off and an excess of ammonium oxalate added to precipitate group IV. The residue is filtered and heated with about 15 ml of 50% acetic acid. Barium goes into the filtrate and is confirmed as chromate. A little of the strontium passes into the filtrate, but it does not respond to the chromate test in acetic acid. The residue containing the oxalates of calcium and strontium is dissolved in dilute nitric acid and treated with ammonium sulfate. Strontium F;
sulfate is removed and the filtrate is neutralized with ammonia. A little oxalate may also be added. Calcium is reprecipitated as oxalate. The filtrate of the calcium group is taken up for group V. The titan yellow test for magnesium is applied as below to overcome the interference due to manganese. The solution is boiled with sodium peroxide. Manganese forms Mn02. HzO; and magnesium forms Mg(OH)=along with a little Mg3(F'O&. The residue is filtered, washed off the adhering alkali, and shaken with cold 0.02 N acetic acid. Only magnesium passes to the filtrate which is treated with sodium hydroxide and titan yellow. However, if
the amount of MnOpis quite small then the magnesium test remains unobscured and is directly applied, as the black particles of MnOz do not adsorb titan yellow. The same separation of magnesium and manganese is recommended if magnesium is to be tested as phosphate. If interfering organic acids are also present then they are oxidized with KMnO, after boiling off HB from the group I1 f i l t ~ a t e . ~Potassium and manganese are tested for before the oxidation. POONIA, N. S., BAAGWAT, W. Y.,J. CHEM.EDUC.,43, 424 (1966).
Volume 44, Number 8, August 1967
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