20 1 1. The last experiment in Zhejiang 26 was designed to test Fe2+. Why does hydrochloric acid have to be acidified?

Fe ~ (2+) is stable only under acidic conditions, and Fe(OH)~ 2 precipitates when the PH value is slightly higher. It is impossible for Fe2+ to react with sulfuric acid to produce precipitation. Unless it is concentrated sulfuric acid, Fe2+ will be oxidized without precipitation. For example, it is enough for Fe to react with dilute sulfuric acid, which will dissolve Fe, so the upstairs statement is wrong. Generally speaking, when iron reacts with concentrated sulfuric acid, a passivation reaction will occur, and a solid oxide protective layer will be formed on the surface of iron. When heated, Fe2(SO4)3 will be generated.