硫代硫酸钠标准溶液的配制与标定实验基准物质k2cr2o7 1·11·4g的取量是怎样

2025-03-15 21:29:20
推荐回答(1个)
回答1:

加入过量的碘是要它与K2Cr2O7完全反应得到产物I2(单质碘)然后用生成的碘在定粉溶液做指示剂下用硫代硫酸钠来滴定,滴定终点蓝色褪去溶液变为绿色,加盐酸是要它在酸性条件下反应,不然K2Cr2O7与碘化钾反应很慢的造成误差太大,但酸度太大碘离子易被氧气氧化造成误差所以用硫代硫酸钠溶液滴定前要加水稀释,反应要放在暗处是因为碘易升华在光条件下造成损失,要放一段时间是因为刚生成的是碘蒸气,碘蒸气有些附在壁上,所以反应完摇一下然后放到暗处保存一段时间。(1)加KI而不加HCl溶液
那么这个反应时间长也反应得不完全计算K2Cr2O7的量少了反应得到的碘少了继而硫代硫酸钠溶液滴定用量少测出硫代硫酸钠溶液浓度偏高。
(2)加酸后不放置暗处
这样会造成碘蒸气升华到壁上或其他地方造成碘减少继而硫代硫酸钠溶液滴定用量少测出硫代硫酸钠溶液浓度偏高。
(3)不放置或少放置一定时间即加水稀释,这样会造成碘蒸气在壁上还没流下来,造成碘减少继而硫代硫酸钠溶液滴定用量少测出硫代硫酸钠溶液浓度偏高。

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