Calcium chromate is an inorganic compound with the formula CaCrO₄, ''i.e.'' the chromate salt of

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...

. It is a bright yellow solid which is normally found in the

dihydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

form CaCrO₄·2H₂O. A very rare anhydrous

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

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 Hexavalent chromium (chromium(VI), Cr(VI), chromium 6) is chromium in any chemical compound that contains the element in the +6 oxidation state (thus hexavalent). Virtually all chromium ore is processed via hexavalent chromium, specifically the ...

compounds such as chromate salts.

Synthesis and reactions

Calcium chromate is formed from the

salt metathesis reaction A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding a ...

sodium chromate Sodium chromate is the inorganic compound with the formula Na2CrO4. It exists as a yellow hygroscopic solid, which can form tetra-, hexa-, and decahydrates. It is an intermediate in the extraction of chromium from its ores. Production and react ...

and

calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Ca ...

: :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 An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

, oxidising organic compounds (''e.g.'' alcohols) or reducing agents (''e.g.'' metals) to the corresponding

carbonyl compounds In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...

or metal oxides while the chromium(VI) centre in CaCrO₄ is reduced to chromium(III). Solid calcium chromate will react explosively with hydrazine. It will also burn violently if mixed with boron and ignited, thereby posing a fire hazard.

Uses

The compound is occasionally used as a yellow inorganic

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

, or a corrosion inhibitor as part of the

chromate conversion coating Chromate conversion coating or alodine coating is a type of conversion coating used to passivate steel, aluminium, zinc, cadmium, copper, silver, titanium, magnesium, and tin alloys. The coating serves as a corrosion inhibitor, as a primer ...

procedure. It has been also utilised in chromium electroplating, in photochemical processing, and as an industrial

waste treatment Waste treatment refers to the activities required to ensure that waste has the least practicable impact on the environment. In many countries various forms of waste treatment are required by law. Solid waste treatment The treatment of solid wastes ...

. All applications suffer from the high toxicity of chromium(VI) species to humans, with chromates listed as

IARC Group 1 Substances, mixtures, and exposure circumstances in this list have been classified as group 1 by the International Agency for Research on Cancer (IARC): The agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures tha ...

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

s while also very corrosive (''e.g.'' capable of producing permanent eye damage) and

genotoxic Genotoxicity is the property of chemical agents that damage the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with mutagenicity, all mutagens are genotoxic, but some genotoxic s ...

References

{{Chromates and dichromates Chromates Calcium compounds Inorganic pigments