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在分析化学定性分析教学中,按硫化氢系统分组法将阳离子分为V个组。第Ⅲ组阳离子的分析方法甚多,Tenbusch等曾总结了13种分离法,但最常用的组内分离一般有两种方法即氨法和碱法。按氨法分离时,部分Mn~(2+)生成MnO(OH)_2而留在沉淀中,部分Co(OH)_2发生共沉淀,造成Mn_(2+),Co~(2+)两边跑,即一部分随Fe(OH)_3,Al(OH)_3,Cr(OH)_3共沉淀下来,一部分留在溶液中,使分离不完全,检出有一定困难。按碱法分离时,部分Zn(OH)_2被带下共沉淀,因而在检出时易丢Zn~(2+)。我们在近几年的实验课教学中,改进了阳离子第Ⅲ组组内分离条件。分离效果好,克服了碱法和氨法分离的缺点。
Analytical chemistry qualitative analysis teaching, according to hydrogen sulfide system grouping method will be divided into V groups of cations. There are many methods for the analysis of group III cation. Ten kinds of separation methods have been summarized by Tenbusch et al., But the two most commonly used methods for group separation are ammonia method and alkali method. When Mn (2 +) was separated by ammonia method, part of Mn (2+) generated MnO (OH) _2 and remained in the precipitate. Some Co (OH) _2 were coprecipitated, resulting in Mn2 + and Co2 + , A part of which was coprecipitated with Fe (OH) 3, Al (OH) 3, Cr (OH) 3 and some remained in the solution, resulting in incomplete separation and some difficulty in detection. When separated by the alkaline method, a part of Zn (OH) 2 is co-precipitated, so it is easy to lose Zn2 + when it is detected. In the experimental teaching in recent years, we improved the conditions for the separation in the group III of the cation. Separation effect is good, to overcome the shortcomings of alkali and ammonia separation.