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分析方法称取0.2500克试样置于干燥的50ml三角烧瓶中,用移液管加入2ml浓硫酸、1克KHSO_4电炉微热,试样溶解后空气中冷却,加入10ml水,10ml 0.2MEDTA溶液,放置15分(亦可加热至沸腾),加入固体六次甲基四胺14～18克,调整pH为5～6,水20ml,这时溶液变清(仅剩少量硫磺絮状物),将试液转移入150ml的三角烧瓶中,加0.5%二甲酚橙指示剂4滴,用0.1M ZnCl_2溶液滴定至快到终点改用0.01M ZnCl_2标准溶液滴定至溶液变为红色,不记读数。加入固体氟化铵2克,放置10分钟,再用0.01M ZnCl_2标准溶液滴定至红色,记下读数。
Analysis method Weigh 0.2500 g sample was placed in a dry 50ml conical flask, pipette 2ml of concentrated sulfuric acid, 1 g KHSO_4 electric furnace micro-heat, the sample was dissolved in air cooled, was added 10ml of water, 10ml 0.2MEDTA solution, Place 15 minutes (can also be heated to boiling), add hexamethylenetetramine 14 to 18 grams of solid, adjust pH to 5 ~ 6, water 20ml, when the solution becomes clear (only a small amount of sulfur floc), the Transfer the test solution into a conical flask of 150ml, add 4 drops of 0.5% xylenol orange indicator, titrate with 0.1M ZnCl 2 solution till the end point and titrate with 0.01M ZnCl 2 standard solution until the solution turns red, without counting. Add 2 g of solid ammonium fluoride and allow to stand for 10 minutes. Titrate again with 0.01 M ZnCl 2 standard solution till red, and write down the reading.