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.

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• 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.

::2 CrO42- + 2 H3O+ ? Cr2O72- + 3 H2O

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:This equilibrium can be pushed towards dichromate by lowering the pH (making the solution more acidic) or in the other direction towards chromate by raising the pH to basic. This is a classic example of Le Chatelier's principle at work.

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• 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.

Salt: : This article is about the general chemical term salt. For the everyday meaning, see edible salt or its main ingredient, sodium chloride. For other meanings of the word salt, see salt (disambiguation)....

PH: pH is a measure of the activity of hydrogen ions (H+) in a solution and, therefore, its acidity or alkalinity. In aqueous systems, the hydrogen ion activity is dictated by the dissociation constant of water (Kw) = 1.011 × 10−14 at 25 ?C) and interactions with other ions in solution. D...

Basic: The acronym BASIC, depending on context, may stand for:...