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Safety data sheet (SDS) Fisher Scientific: Related compounds Other anions. Potassium dichromate ... Potassium chromate is the inorganic compound with the formula K 2 ...
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.
Chromyl chloride can be prepared by the reaction of potassium chromate or potassium dichromate with hydrogen chloride in the presence of sulfuric acid, followed by distillation. [3] [4] K 2 Cr 2 O 7 + 6 HCl → 2 CrO 2 Cl 2 + 2 KCl + 3 H 2 O. The sulfuric acid serves as the dehydration agent.
The hydrogen chromate ion may be protonated, with the formation of molecular chromic acid, H 2 CrO 4, but the pK a for the equilibrium H 2 CrO 4 ⇌ HCrO − 4 + H + is not well characterized. Reported values vary between about −0.8 and 1.6. [4] The dichromate ion is a somewhat weaker base than the chromate ion: [5]
Partial predominance diagram for chromate. Molecular chromic acid, H 2 CrO 4, in principle, resembles sulfuric acid, H 2 SO 4. It would ionize accordingly: H 2 CrO 4 ⇌ [HCrO 4] − + H + The pK a for the equilibrium is not well characterized. Reported values vary between about −0.8 to 1.6. [4]
Potassium hypochromate decomposes in water to form chromium(III) oxide and potassium chromate when alkali is not present or low. [1] Potassium hypochromate also reacts with acids such as hydrochloric acid to form chromium(III) oxide, potassium chromate, and potassium chloride: [2] 6 K 3 CrO 4 + 10 HCl → 4 K 2 CrO 4 + Cr 2 O 3 + 5 H 2 O + 10 KCl
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 chlorochromate was originally prepared by treating potassium dichromate with hydrochloric acid. An improved route involves the reaction of chromyl chloride and potassium chromate: [5] K 2 CrO 4 + CrO 2 Cl 2 → 2KCrO 3 Cl. The salt consists of the tetrahedral chlorochromate anion. The average Cr=O bond length is 159 pm, and the Cr-Cl ...