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于 pH 8左右的溶液中,利用钝化液中的 CrO_4~(-2)作指示剂,直接以硝酸银滴定。槽液成份为:Na_2Cr_2O_7·2H_2O 100～150克/升,H_2SO_4 4～6克/升,NaCl 5～8克/升。吸取槽液2毫升(或吸取10毫升槽液于100毫升容量瓶中,加水稀释至刻度,取20毫升)于300毫升锥形瓶中,加水100毫升,加5%氢氧化钾溶液5毫升,此时溶液应呈亮黄色,加入酚酞指示剂应呈红色,否则须再加氢氧化钾溶液至红色出现。滴加5%醋酸
In pH 8 or so solution, the use of passivation solution CrO_4 ~ (-2) as an indicator, the direct titration with silver nitrate. The bath composition is as follows: Na 2 Cr 2 O 7 · 2H 2 O 100 ~ 150 g / L, H 2 SO 4 4 ~ 6 g / L, NaCl 5 ~ 8 g / L. (Or draw 10 ml of bath in 100 ml volumetric flask, diluted with water to the mark, take 20 ml) in 300 ml Erlenmeyer flask, add water 100 ml, add 5% potassium hydroxide solution 5 ml, At this point the solution should be bright yellow, add phenolphthalein indicator should be red, otherwise it must be coupled with potassium hydroxide solution to the red appear. Add 5% acetic acid dropwise