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磷钼酸铵法测定磷的洗涤问题,国内外都做了大量的工作,在洗涤过程中,最后均采用稀硝酸钾溶液洗涤。最近国内有些单位或国外都有报导,利用中性水洗涤所得的结果偏高,但他们都未说明其原因。我们认为,这是由于磷钼酸铵沉淀的组成是:(NH_4)_2H[P(Mo_3O_(10))_4]·H_2O。该沉淀先用稀硝酸溶液洗涤,后用中性水洗涤,沉淀组成保持不变。该沉淀溶于过量的氢氧化钠标准溶液中:(NH_4)_2H[P(Mo_3O_(10))_4]·H_2O+27OH~-=PO_4~(3-)+
Phosphomolybdate ammonium method for the determination of phosphorus washing problems, both at home and abroad have done a lot of work, in the washing process, the last are washed with dilute potassium nitrate solution. Recently some units in China or abroad have reported that the use of neutral water washing results obtained high, but they did not explain the reason. In our opinion, this is due to the composition of ammonium phosphomolybdate precipitation: (NH 4) _2H [P (Mo 3 O_ (10)) _ 4] .H 2 O. The precipitate was first washed with dilute nitric acid solution, followed by neutral water washing, the precipitate composition remained unchanged. The precipitate is dissolved in an excess of sodium hydroxide standard solution: (NH 4) 2 H [P (Mo 3 O 10) 4] H 2 O + 27OH ~ - = PO 4 ~ (3 -) +