Chromium(VI) oxide peroxide

Chromium(VI) peroxide (CrO₅) or chromium oxide peroxide is an unstable compound formed by the addition of acidified hydrogen peroxide solutions to solutions of metal chromates, such as sodium chromate. The generally yellow chromates turn to dark blue-brown as chromium(VI) peroxide is formed. The metal chromate reacts with hydrogen peroxide and an acid to give chromium peroxide, water, and the metal salt of the acid.