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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.
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 +1: 1 2 helium: He 0 18
CrO 2 was first prepared by Friedrich Wöhler by decomposition of chromyl chloride. Acicular chromium dioxide was first synthesized in 1956 by Norman L. Cox, a chemist at E.I. DuPont, by decomposing chromium trioxide in the presence of water at a temperature of 800 K (527 °C; 980 °F) and a pressure of 200 MPa.
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.
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 compounds, the oxidation numbers are the same as the element's ionic charge.
It is prepared by treating potassium dichromate with potassium hydroxide: . K 2 Cr 2 O 7 (aq) + 2 KOH → 2 K 2 CrO 4 + H 2 O. Or, the fusion of potassium hydroxide and chromium trioxide:
The chemical composition of chromite can be represented as FeCr 2 O 4, with the iron in the +2 oxidation state and the chromium in the +3 oxidation state. [5] bauxite, when presented as an ore, or in massive form, forms as fine granular aggregates. The structure of the ore can be seen as platy, with breakages along planes of weakness. Chromite ...
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