What does dichromate mean?
A dichromate is any chemical compound containing the dichromate anion, Cr₂O₇²⁻, formed from two linked chromium-oxygen tetrahedra sharing an oxygen atom. Dichromates are strikingly colored — usually vivid orange-red — and are strong oxidizing agents, which makes them valuable in laboratory analysis, metal treatment, leather tanning, and photography. The most familiar examples are potassium dichromate and ammonium dichromate; the latter fuels the well-known classroom 'volcano' experiment, burning to leave a mound of green chromium oxide. The word derives from Greek roots meaning 'two' and 'color', reflecting the relationship between chromates and dichromates, which convert into each other depending on acidity. Because they contain hexavalent chromium, dichromates are toxic and carcinogenic, so their industrial use has declined sharply under modern environmental and safety regulations. Today the term belongs firmly to scientific and technical registers rather than everyday speech.
nounA salt or ester of dichromic acid containing the divalent anion Cr₂O₇²⁻, typically orange-red and strongly oxidizing; the best-known example is potassium dichromate.
- Any salt or ester containing the dichromate anion Cr₂O₇²⁻, especially potassium dichromate, used as an oxidizing agent in chemistry and industry.
"The chemist added a few crystals of potassium dichromate to the solution, turning it a vivid orange."
"In acidic solution, the dichromate ion is a powerful oxidizing agent used in redox titrations."
"Before stricter safety rules took hold, sodium dichromate was widely used as a corrosion inhibitor in industrial cooling systems."
Regular plural; used when referring to several different salts or esters of the dichromate anion.
"Chromates and dichromates interconvert reversibly depending on the pH of the solution."
Ammonium dichromate powers the classic 'volcano' chemistry demo — one burning pile that erupts into a mountain of green ash without any actual lava.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dichromate
The word dichromate combines the Greek prefix di-, meaning 'two', with chromate, which itself comes from Greek chrōma ('color') via the element name chromium, coined by French chemist Louis-Nicolas Vauquelin when he isolated the metal in the late eighteenth century. The 'di-' refers to the two chromium atoms in the Cr₂O₇²⁻ anion. The older term bichromate uses the Latin-derived bi- for the same idea and was common in nineteenth-century usage before falling out of favor. The root chrōma also gives English cognates such as chromatic, monochrome, and polychrome.
Related word forms
How dichromate is actually used
Strictly a technical term belonging to chemistry and related industries; it rarely appears outside scientific writing. Because many dichromates contain toxic hexavalent chromium, the word often carries associations of hazard and regulation. The older synonym 'bichromate' is now largely superseded.
Easily confused with dichromate
A chromate contains the singly-charged anion CrO₄²⁻ and is yellow, whereas a dichromate contains the doubly-charged Cr₂O₇²⁻ anion and is orange; the two interconvert with changes in pH.
Dichromatic is an adjective meaning having two colors or two-color vision, while dichromate is a noun naming a chemical compound.