Preparation of a red salt precipitate which has interesting properties
name: Partial reduction of copper to form a salt of copper in a mixed oxidation state
Sodium metabisulfite has reducing properties. Therefore, part of the Cu(II) may be reduced to Cu(I). The reaction proceeds as ion exchange in this solution, which explains the formation of a red precipitate of mixed salt, which contains copper in two oxidation states.
After addition of hydrochloric acid, Cu(II) passes into the solution in the form of CuCl2, and Cu(I) remains as a precipitate of CuCl which has a white color.
Cu(II) forms stable complexes with ammonia, soluble in water and colored in blue.