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在化学教学中,实验占有重要的地位。一般来讲实验现象与教材结论是一致的。但是有时由于试剂不纯,操作不当或其他因素也有得不到相应的结果,甚至还有出现了相反的结论。我在实验教学中就有一些失败的教训。1、要保证实验药品和试剂有足够的纯度检验乙醛CH_3CHO、葡萄糖含有醛基(-CHO)的银镜反应,一般都能做成功,但有一次,总是看不到银镜的生成,只能看到溶液呈现黑色。经多次试验分析,发现是氨水不纯。我们用NH_4HCO_3与NaOH共热自制了一些氨水,由于碳酸氢铵过量,产生的CO_2与氨气一同挥发被水吸收了,氨水中有
In chemistry teaching, experiment occupies an important position. In general, the experimental phenomenon is consistent with the conclusion of the teaching materials. However, sometimes due to impure reagents, improper operation or other factors, there is no corresponding result, and even the contrary conclusion has emerged. I have some failed lessons in experimental teaching. 1, to ensure that the experimental drugs and reagents have enough purity to test acetaldehyde CH_3CHO, glucose containing aldehyde group (-CHO) of the silver mirror reaction, generally can be successful, but once, always can not see the generation of silver mirror, Only see the solution appear black. After several tests and analysis, it was found that the ammonia is impure. We used NH_4HCO_3 and NaOH to heat some ammonia water. Due to excessive ammonium bicarbonate, the produced CO_2 was volatilized with ammonia and absorbed by water. In ammonia water,