chromate

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chromate

any salt or ester of chromic acid. Simple chromate salts contain the divalent ion, CrO42--, and are orange

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

chromate

[′krō‚māt]
(inorganic chemistry)
CrO42-
An ion derived from the unstable acid H2CrO4.
A salt or ester of chromic acid.
(mineralogy)
A mineral characterized by the cation CrO42-.

chromate

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