Chromate

Chromate is the yellow CrO₄²⁻ oxyanion, with chromium in the +6 oxidation state. It forms salts and participates in pH-dependent equilibria with hydrogen chromate and dichromate.

Hydrogen chromate: Hydrogen chromate is the HCrO₄⁻ oxyanion formed when chromate accepts a proton. Acidifying chromate shifts some ions into this protonated form.
Oxyanion: An oxyanion is a negatively charged polyatomic ion containing oxygen bonded to another element. Chromate is an oxyanion built around chromium and oxygen.
Lead chromate: Lead chromate is a yellow lead(II) salt, PbCrO₄, historically used as a pigment. Its vivid yellow color made a chromate salt valuable in paints.
Chromium(III): Chromium(III) is chromium in the +3 oxidation state, common in stable salts and biological systems. Chromium(III) differs from chromate’s chromium(VI) in oxidation state and typical toxicity.
RoHS Directive: The RoHS Directive is a European Union law restricting hazardous substances in electrical and electronic equipment. Its restrictions helped phase out chromium(VI) compounds in many products.
Dichromate: Dichromate is the orange Cr₂O₇²⁻ oxyanion, containing two chromium(VI) centers. Acidic conditions favor this condensed form over yellow chromate.
Chromium: Chromium is a transition metal with the chemical symbol Cr and atomic number 24. Chromium is the central element in the chromate ion.
Zinc chromate: Zinc chromate is a yellow chromium(VI) compound formerly used in corrosion-resistant coatings. It supplied chromate ions in protective coatings for metals.
Permanganate: Permanganate is the purple MnO₄⁻ oxyanion, with manganese in the +7 oxidation state. It is another strongly oxidizing, colored oxyanion, but contains manganese instead of chromium.
Occupational exposure to chromium(VI): Occupational exposure to chromium(VI) occurs when workers encounter its compounds through inhalation or skin contact. Chromate-containing coatings and pigments create workplace exposure risks.

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