Chromate - CrO42-

What is Chromate?

Chromates are the salts of chromic acid which contains the chromate anion with the chemical formula CrO42 and usually have an intense yellow color.

Chromate is the oxoanion which results from the removal of protons from chromic acid. It is also called chromium oxoanion or divalent inorganic anions. The most commonly used chromate salts are sodium and potassium salts.

Table of Contents

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 CrO42

Physical Properties of Chromate – CrO42-

Odour Odourless
Appearance Yellow powder
Valency 2
Solubility Generally insoluble in water.

Chemical Properties of Chromate – CrO42-

          • Chromate ion acts as a strong oxidizing agent in acid solution. In an 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 to form 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 are 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 non-toxic. Industrial crayons are made with lead chromate which is not harmless.
        • Used in chrome plating to prevent corrosion.

Frequently Asked Questions


What is chromate used for?

It is mainly used as an inhibitor of corrosion, as a primer, as a decorative finish, or to maintain electrical conductance. The process takes its name from the chromate present in chromic acid, also known as hexavalent chromium, the most commonly used chemical in the immersion bath phase by which the coating is applied.


Is CrO4 an acid or base?

The chromate ion is the predominant species in alkaline solutions but in acidic solutions, dichromate can become the predominant ion.


How do you make a chromate solution?

Formulated in yellow chromate. Dissolve the dichromate and the chromic acid first with a little water, then add the nitric and sulphuric and carry the volume with water up to 50 litres to dissolve both.


Are chromate and chromium the same thing?

Chrome is an item that is short for chromium, which is applied as an electroplated finish. On the other hand, Chromate is used to characterize a process resistant to corrosion that is known as a conversion finish, rather than an additive finish.


What is potassium chromate used for?

It is used as a fungicide in chemical processing, for making pigments for paints and inks, and for producing other chromium compounds. Potassium chromate is a potassium salt in a ratio of 2:1 consisting of potassium and chromate ions. It has a role as both a carcinogenic and an oxidizing agent.

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