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Chromates and '''dichromates''' are Salt s of Chromic Acid and dichromic acid, respectively. Chromate salts contain the '''chromate ion''', Cr O 42−, and have an intense yellow color. Dichromate salts contain the '''dichromate ion''', Cr2O72−, and have an intense orange color.


CHARACTERISTICS



::2 CrO42− + 2 H3O+ ⇌ Cr2O72− + 3 H2O

: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.
  • 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 Reagent s. 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.

  • Chromate Conversion Coating s are applied to metals for corrosion protection, and to improve paint adhesion.

  • The use of chromate compounds in manufactured goods is restricted in the EU (and by market commonality the rest of the world) by EU Parliament directive 2002/95/EC



SEE ALSO




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