Chromic acid

In chemistry, chromic acid (or 'Jones reagent') is a chromium (Cr) compound, yet to be isolated, that would have the formula H₂CrO₄. There is a related acid, also yet to be isolated called dichromic acid with the formula H₂Cr₂O₇. While these acids are not available, they are known through their divalent anions (chromate and dichromate respectively) and the compounds formed from them. Please note that the acid anhydride of chromic acid exists, chromium trioxide (CrO₃), and that industrially, this compound is sometimes sold as "chromic acid". This compound is an intensely-colored dark red/orange brown, water-soluble, granular solid which is stable by itself, but is a strong oxidant which will react when mixed with many things that can be oxidized. In all of the compounds discussed here, the element chromium is in oxidation state +6 (or VI). Chromium (VI) is often referred to as hexavalent chromium. Although chromium can exist in a number of oxidation states, hexavalent chromium is commonly reduced a +3 oxidation state, where the Cr⁺³ ion is a distinctively different blue green color.

Chromic acid solutions are generally acidified aqueous solutions of chromate or dichromate salts. These solutions tend to be powerful oxidants, capable of destroying all organics in glassware and so often used for the cleaning of glass. Such solutions are often red-brown, orange, or yellow colored depending on concentration.