Chromate - CrO42-

What is Chromate?

Chromates are the salts of chromic acid which contains the chromate anion with chemical formula CrO42 and usually have an intense yellow color. It is the oxoanion which results from the removal of protons from chromic acid. It is also called as chromium oxoanion or divalent inorganic anions. The most commonly used chromate salts are sodium and potassium salts.

IUPAC name – dioxido(dioxo)chromium

CrO42-

Chromate

Density

2.73 g/cm³

Molecular Weight/ Molar Mass

194.1896 g/mol

Conjugate acid‎

‎Chromic acid (H2CrO4)

Oxidation State

+6

Chemical Formula

CrO42-

Chromate Structure – CrO42-

Chromate Structure

Physical Properties of Chromate – CrO42-

Odour

Odorless

Appearance

Yellow powder

Valency

2

Solubility

Generally insoluble in water.

Chemical Properties of Chromate – CrO42-

  • Chromate ion acts as a strong oxidising agent in acid solution. In alkaline solution chromate ion combines with water to form chromium(III) hydroxide.
  • CrO42− + 4 H2O + 3 e → Cr(OH)3 + 5 OH

  • Chromate as its potassium salt reacts with barium nitrate forms barium chromate and potassium nitrate.
  • K2CrO4 + Ba(NO3)2 ↔ BaCrO4 + 2KNO3

Uses of Chromate – CrO42-

  • Sodium and potassium salts of chromate are highly corrosive and used in enamels, finishing leather and for rust proofing metals.
  • Yellow crystals of potassium chromate is used as a pigment in dye and in inks. It is toxic by ingestion.
  • Children crayons are made by wax is usually paraffin and is nontoxic. Industrial crayons made by lead chromate which is not harmless.
  • Used in chrome plating to prevent corrosion.

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