Calcium chromate is an inorganic compound with the formula CaCrO₄, ''i.e.'' the chromate salt of calcium. It is a bright yellow solid which is normally found in the dihydrate form CaCrO₄·2H₂O. A very rare anhydrous mineral form exists in nature, which is known as chromatite. The compound is occasionally used as a pigment, but this usage is limited due to the very toxic and carcinogenic nature of hexavalent chromium compounds such as chromate salts.

Synthesis and reactions

Calcium chromate is formed from the salt metathesis reaction of sodium chromate and calcium chloride: :Na₂CrO₄ + CaCl₂ → CaCrO₄ + 2 NaCl In aqueous solution the dihydrate is obtained, which loses water to afford the anhydrate at 200 °C. It is an oxidiser, oxidising organic compounds (''e.g.'' alcohols) or reducing agents (''e.g.'' metals) to the corresponding carbonyl compounds or metal

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

s while the chromium(VI) centre in CaCrO₄ is reduced to

chromium(III) Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

. Solid calcium chromate will react explosively with

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...

. It will also burn violently if mixed with

boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...

and ignited, thereby posing a fire hazard.

Uses

The compound is occasionally used as a yellow inorganic pigment, or a corrosion inhibitor as part of the chromate conversion coating procedure. It has been also utilised in chromium

electroplating Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be ...

, in photochemical processing, and as an industrial waste treatment. All applications suffer from the high toxicity of chromium(VI) species to humans, with chromates listed as IARC Group 1 carcinogens while also very corrosive (''e.g.'' capable of producing permanent eye damage) and genotoxic.

References

{{Chromates and dichromates Chromates Calcium compounds Inorganic pigments