Chromate: Encyclopedia - Chromate

Chromate

Chromates and dichromates are salts of chromic acid and dichromic acid, respectively. Chromate salts contain the chromate ion, CrO₄^2-, and have an intense yellow color. Dichromate salts contain the dichromate ion, Cr₂O₇^2-, and have an intense orange color.

Chromate - Characteristics

• The chromium atoms are in oxidation state +6 in both, and the chromate and dichromate ions are fairly strong oxidizing agents. Chromium in the +6 (or VI) oxidation state is often referred to as hexavalent chromium.
• In an aqueous solution, chromate and dichromate anions are in a chemical equilibrium.

• They are used in environmental analysis to measure chemical oxygen demand (COD).
• They are carcinogenic. All hexavalent chromium compounds are considered toxic and carcinogenic.
• When used as oxidizing agents or titrants in a redox chemical reaction, they will turn into trivalent chromium, Cr³⁺, which has a distinctively different blue-green color.
• The sodium (Na⁺), potassium (K⁺), and ammonium (NH₄⁺) salts are water soluble granular solids and are the most commonly used chromate or dichromate chemical reagents. Most chromate and dichromate salts of heavy metals, lanthanides or alkaline earth metals are only very slightly soluble in water and are thus of much less usefulness.

See also

• Potassium dichromate - K₂Cr₂O₇

Adapted from the Wikipedia article "Chromate", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki