Hi everybody! Does anyone knows why when a cation is mixed with a strong acid the color of the solution (if it's colored) fades a little bit, depending on the concentration of the acid? For example an "orangy" solution that contains Fe3+, If HCl 2 M is added the color turns yellow, and if H2SO4 6 M is added instead it turns transparent. Is it due to the formation of colorless complexes (like FeCl4-)? Is it even possible that a complex is formed adding only the acid, with an excess of the ligand (like in the first case Cl-)? The same thing happens with, Fe 2+, Co2+, Cr 3+, Ni 2+ and Co2+ solutions ( I did it in the laboratory) , and I'm not able to explain it.