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测定氯根(Cl-)的经典方法是硝酸银沉淀滴定法,由于氯化银和铬酸银的溶度积的差异及两者沉淀颜色的明显不同,使此方法得以应用:Ag++Cl-AgCl↓(白色)2Ag++CrO42-Ag2CrO4↓(砖红色)这个方法应注意的是被滴定溶液的酸碱性范围问题。首先,本方法指示剂的指示产物铬酸银也是沉淀物而且只有生成沉淀才能起到指示作用,由于铬酸(H2CrO4)是个弱酸,其电离常数K∝2=3.1×10-7,因此,当溶液呈酸性时铬酸银就容易溶解:
The classical method of determining chloride (Cl-) is the silver nitrate precipitation titration method, which is applied due to the difference in solubility products between silver chloride and silver chromate and the precipitating color of the two. Ag ++ Cl -AgCl ↓ (white) 2Ag ++ CrO42-Ag2CrO4 ↓ (brick red) This method should be noted that the titration solution is the problem of the pH range. First of all, silver chromate, which is the indicator of the method indicator, is also a precipitate and can only be used as an indicator. Since chromic acid (H2CrO4) is a weak acid and has an ionization constant Kα2 = 3.1 × 10-7, When the solution is acidic silver chromate is easy to dissolve: