定性分析教材中几个值得商榷的问题

SOME QUESTIONS WHICH IS VALUBLE TO BE DISCUSSED IN THE TEOEHING MATERIAL OF QUALITATIVE ANALYSIS

本文以实验为基础,从理论与实践相统一的观点,探讨在定性分析教材中存在的几个问题:(1)沉淀 Fe_2S_3的生成;(2)Sn(Ⅱ)的予先氧化;(3)酸性溶液中 NO^-_3的氧化性。

In this paper three questions which existed in the teaching material of qualitative analysis were discussed on the basis of chemical experiments. 1.Under conditions of analysing group Ⅲ cations in H_2S system,iron reacting with H_2S can only produce FeS. 2.When analysing group Ⅱ cations in H_2S system,it is a better way to oxide tin to Sn(Ⅳ) and then to continue separating and identifying before Sn(Ⅱ) reacts with H_2S to produce sulfide precipitate. 3.Both NO_3^- and NO_2^-,together with strong acid in dilute solution (concentration above 2 mol/l),all have oxidic properties,but in acetic only NO_2^- has oxidic property.