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如果有人问,怎样除去氯化钠溶液中少量的硫酸钠?很多同学会脱口而出地回答:加适量氯化钡溶液,过滤.乍听起来,这种做法无可非议,但仔细推敲,就发现此回答存在问题.为什么呢?问题出在“适量”二字上.氯化钡加少了当然不行,因为SO42-不能全部除尽.那么加多少才是适量呢?有人会说:加到白色沉淀不再增加为止.可是在溶液中已生成了较多白色沉淀后,再加入氯化钡溶液,是否又生成了少量白色沉淀是很难观察出来的.采用取上层清液检验的办法也不实际,总不能每加入一滴试液就检验一次吧.
If someone asks, how to remove a small amount of sodium sulfate in sodium chloride solution? Many students will blurt out and answer: Add appropriate amount of cesium chloride solution, filter. 乍 Sounds like this is undeniable, but careful scrutiny, it was found that this answer exists Question. Why? The problem lies with the word “moderate”. It is of course not possible to add less cesium chloride, because SO42- cannot be completely eliminated. How much is the appropriate amount? Some people will say: Adding white precipitate is no longer a problem. Increased so far. However, after more white precipitate has been formed in the solution, adding the cesium chloride solution again, it is difficult to observe if a small amount of white precipitate is generated. The method of using the supernatant is also not practical. Don’t test every drop of test solution.