A sample of ammonium dichromate

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. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... In chemistry, salt is a term used for ionic compounds composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. ... In chemistry, chromic acid (or Jones reagent) is a chromium (Cr) compound, yet to be isolated, that would have the formula H2CrO4. ...

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.

2 CrO₄^2- + 2 H₃O⁺ → Cr₂O₇^2- + 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 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.

General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... Properties An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. ... The oxidation state or oxidation number is defined as the sum of negative and positive charges in an atom, which indirectly indicates the number of electrons it has accepted or donated. ... An oxidizing agent is a substance that oxidizes another substance in electrochemistry or redox chemical reactions in general. ... Drinking water This article focuses on water as we experience it every day. ... Chemical equilibrium is the state in which a chemical reaction proceeds at the same rate as its reverse reaction; the rates of the forward and reverse reactions are equal, and the concentration of the reactants and products stop changing. ... The title of this article is shown beginning with a capital letter due to technical restrictions. ... The common (Arrhenius) definition of a base, also known as an alkaline compound, is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... In chemistry, Le Chateliers principle can be used to predict the effect of a change in conditions on a chemical equilibrium. ... In environmental chemistry, the chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. ... In pathology, a carcinogen is any substance or agent that promotes cancer. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... A chemical reaction is a process that results in the interconversion of Chemical substances . ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... Fumes from hydrochloric acid and ammonia forming a white cloud of ammonium chloride The Ammonium cation is a positively charged polyatomic ion of the chemical formula NH4+ and a molecular mass of 18. ... A reagent is any substance used in a chemical reaction. ... For other meanings, see heavy metal The term heavy metal may have various more general or more specific meanings. ... The lanthanide series is the 14 rare earth chemical elements which lie between lanthanum and ytterbium on the periodic table. ... The alkaline earth metals are the series of elements in Group 2 of the periodic table: beryllium, magnesium, calcium, strontium, barium and radium (not always considered due to its very short half-life). ...

See also

• Potassium dichromate - K₂Cr₂O₇

Potassium dichromate, K2Cr2O7 is used in oxidation reactions. ...

External links

• IARC Monograph "Chromium and Chromium compounds"