Chromium hydroxide: gray-green solid, amphoteric hydroxide.
It reacts with alkali to form a bright green solution with a hydroxyl coordination number of 4 or 6, which is still under dispute
If the coordination number is 4, the valence of the acid radical is -1
Cr(OH)3+OH(-)=[Cr(OH)4](-)
If the coordination number is 6, the valence of the acid radical is -3;
Cr(OH)3+3OH(-)=[Cr(OH)6](3-)
Reacts with acid to form a purple solution,
Cr(OH)3+3H2O+3H(+)=[Cr(H2O)6](3+)
However, if it is hydrochloric acid, the reaction product will turn from purple to blue and finally to green as the concentration of hydrochloric acid increases.This is a phenomenon formed by the exchange of ligand water with free chloride ions.
Cobalt hydroxide: generally refers to the precipitate in the solution, +2 valence, pink solid.
Heating produces dark brown solid Cr2O3;
Cobalt hydroxide is placed slowly to generate dark brown Cr2O3xH2O.