Chromate (redirected from Chromate Mineral)

chromate

any salt or ester of chromic acid. Simple chromate salts contain the divalent ion, CrO₄^2--, and are orange

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chromate [′krō‚māt]

(inorganic chemistry)

CrO₄^2-

An ion derived from the unstable acid H₂CrO₄.

A salt or ester of chromic acid.

(mineralogy)

A mineral characterized by the cation CrO₄^2-.

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chromate

To coat a metal surface with a rust-inhibiting primer of lead or zinc chromate.

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Chromate 

any one of a group of salts of chromic acid and isopolychromic acids. The salts of chromic acid, H₂CrO₄, namely monochromates or simply chromates, are discussed below.

Chromates are stable only in an alkaline medium; upon acidification, they are converted to dichromates. Potassium chromate and sodium chromate are the most important chromates.

Potassium chromate, K₂CrO₄, is a yellow crystalline substance, with a density of 2.732 g/cm³ and a melting point of 968.3°C. It is readily soluble in water: 62.9 g at 20°C and 79.2 g at 100°C in 100 g of water. It is produced by the action of potassium hydroxide, KOH, on potassium dichromate, K₂Cr₂O₇.

Sodium chromate, Na₂CrO₄, is also a yellow crystalline substance, with a density of 2.72 g/cm³ and a melting point of 790°C. A hygroscopic compound, it is soluble in water: 80.2 g in 100 g of water at 19.5°C. It is produced by roasting the natural chromite FeCr₂O₄ with dolomite and sodium carbonate at 1150°–1200°C, then leaching out Na₂CrO₄ from the sintered mass formed, and finally subjecting the solution to evaporation and crystallization.

Sodium chromate and potassium chromate are used as chemical reagents, as mordants for dyeing textiles, and as components of tanning solutions in the leather industry. They are also used for seed treatment and as wood preservatives.

REFERENCE

Pozin. M. E. Tekhnologiia mineral’nykh solei, 4th ed., parts 1–2. Leningrad, 1974.

A. B. SUCHKOV