Chromate salts contain the chromate anion, CrO₄²⁻. Dichromate salts contain the dichromate anion, Cr₂O₇²⁻. They are oxyanions of chromium in the oxidation state +6. They are moderately strong oxidizing agents.

Chromates react with hydrogen peroxide giving products in which peroxide, O₂²⁻, replaces one or more oxygen atoms. In acid solution the unstable blue peroxo complex Chromium(VI) oxide peroxide, CrO(O₂)₂, is formed; it is an uncharged covalent molecule which may be extracted into ether. Addition of pyridine, results in the formation of the more stable complex CrO(O₂)₂py.

In aqueous solution, chromate and dichromate anions exist in a chemical equilibrium.

The predominance diagram shows that the position of the equilibrium depends on both pH and the analytical concentration of chromium. The chromate ion is the predominant species in alkaline solutions, but dichromate can become the predominant ion in acidic solutions. The change in colour with pH from yellow (chromate) to orange (dichromate) and the reversible nature of the equilibrium have been beautifully illustrated