Sudarshan Lal
and S. N. Srivastava Agra College Agra, U. P., India
Reagents for the Qualitative Analysis of Ce(W)-Ce(W) Mixtures
A variety of instrumental methods exists for the determination of Ce(II1) and Ce(IV). Also it is known that Ce(1V) complexes more strongly because of its smaller ionic radius. We here report a series of comparisons between the behavior of Ce(II1) and Ce(IV) toward several familiar analytical reagents. Thymol Blue. The reagent is prepared in methyl alcohol by adding 5 mg to 10 ml of methanol. The solution of Ce(IV) and Ce(II1) may be aqueous or alcoholic. Ce(IV) gives a pink coloration with thymol blue which is readily extractable by ether into a pink upper layer. Ce(II1) gives a yellow solution which is not extractable by ether. The test is applicable both at micro and semimicm scale. Tartrazine. The reagent is prepared by dissolving 35 mg in 10 ml of distilled water. Ce(1V) g'~ v e sa brownish yellow precipitate with the reagent. The minimum amount of Ce(IV) is about 5 X 10W3gm/ml; a lower concentration than this limit will not yield an observable precipitate of Ce(1V). Ce(II1) does not form a precipitate.
424 / Journal of Chemical Educafion
Alizarine. A solution containing 10 mg in 10 ml of ethanol was used as the reagent. Ce(II1) yields a pink color and Ce(1V) gives a yellow color. Favorable results are obtained by spot test analysis where alcoholic or aqueous media are required. Selenous Acid. Ce(1V) yields a yellow-brown precipitate with an aqueous solution of selenous acid while Ce(II1) fails to yield any precipitate. Ce(1V) can be completely removed and Ce(II1) in the filtrate can be detected as a white gelatinous precipitate by the addition of NaF. Potassium Bromate. Cerium(1V) gives a yellowishwhite precipitate with aqueous potassium bmmate solution in neutral or slightly acidic medium. Ce(II1) does not yield any precipitate. Ammonium Molybdate. Ammonium molybdate gives a yellow precipitate with Ce(1V) while a slight turbidity is obtained with Ce(II1). The yellow precipitate in the former case is insoluble in 50% acetic acid, while the turbidity disappears in the presence of acetic acid in the latter case.
