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Two crystalline forms are known, both being very similar to the corresponding potassium sulfate. Orthorhombic β-K 2 CrO 4 is the common form, but it converts to an α-form above 66 °C. [1]
Element Negative states Positive states Group Notes −5 −4 −3 −2 −1 0 +1 +2 +3 +4 +5 +6 +7 +8 +9 Z; 1 hydrogen: H −1: 0 +1: 1 [1]2 helium: He 0
Predominance diagram for chromate. In aqueous solution, chromate and dichromate anions exist in a chemical equilibrium.. 2 CrO 2− 4 + 2 H + ⇌ Cr 2 O 2− 7 + H 2 O. The predominance diagram shows that the position of the equilibrium depends on both pH and the analytical concentration of chromium.
Compounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate. The only binary compound is the volatile chromium(V) fluoride (CrF 5). This red solid has a melting point of 30 °C and a boiling point of 117 °C.
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.
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Oxidation numbers are assigned to elements in a molecule such that the overall sum is zero in a neutral molecule. The number indicates the degree of oxidation of each element caused by molecular bonding. In ionic molecules, the oxidation numbers are the same as the element's ionic charge.
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