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Chromate salts contain the chromate anion, CrO 2− 4. Dichromate salts contain the dichromate anion, Cr 2 O 2− 7. They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of potassium chromate. At yet lower pH values, further condensation to more complex oxyanions of chromium is possible. Both the chromate and dichromate anions are strong oxidizing reagents at low pH ...
Potassium dichromate, K 2 Cr 2 O 7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color.
sodium chromate Na 2 CrO 4 is made yellow by the chromate ion CrO 2− 4. potassium dichromate K 2 Cr 2 O 7 is made red-orange by the dichromate ion Cr 2 O 2− 7. cobalt(II) nitrate hexahydrate Co(NO 3) 2 ·6H 2 O is made red by the chromophore of hydrated cobalt(II) [Co(H 2 O) 6] 2+. copper(II) sulfate pentahydrate CuSO 4 ·5H 2 O is made ...
The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide [27] [28] Chromium is a member of group 6 , of the transition metals . The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.
The oxide is also formed by the decomposition of chromium salts such as chromium nitrate, or by the exothermic decomposition of ammonium dichromate. (NH 4) 2 Cr 2 O 7 → Cr 2 O 3 + N 2 + 4 H 2 O. The reaction has a low ignition temperature of less than 200 °C and is frequently used in “volcano” demonstrations. [9]
Silver dichromate is a chemical compound with the formula Ag 2 Cr 2 O 7. It is insoluble in water and decomposes when treated with hot water. Its anion has a charge of -2.