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The red line on the predominance diagram is not quite horizontal due to the simultaneous equilibrium with the chromate ion. 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 ...
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.
Loss of the second proton occurs in the pH range 4–8, making the ion [HCrO 4] − a weak acid. [citation needed] Molecular chromic acid could in principle be made by adding chromium trioxide to water (cf. manufacture of sulfuric acid). CrO 3 + H 2 O ⇌ H 2 CrO 4. In practice, the reverse reaction occurs: molecular chromic acid dehydrates ...
3 has the corundum structure, consisting of a hexagonal close packed array of oxide anions with 2 ⁄ 3 of the octahedral holes occupied by chromium. Similar to corundum, Cr 2 O 3 is a hard, brittle material (Mohs hardness 8 to 8.5). [4] It is antiferromagnetic up to 307 K, the Néel temperature.
A chromate ester is a chemical structure that contains a chromium atom (symbol Cr) in a +6 oxidation state that is connected via an oxygen (O) linkage to a carbon (C) atom. The Cr itself is in its chromate form, with several oxygens attached, and the Cr–O–C attachment makes this chemical group structurally similar to other ester functional groups.
Chromate and dichromate have equal concentrations. Setting [CrO 2− 4] equal to [Cr 2 O 2− 7] in Eq. 3 gives [CrO 2− 4] = 1 / β 2 [H +] 2 . The predominance diagram is interpreted as follows. The chromate ion is the predominant species in the region to the right of the green and blue lines. Above pH ~6.75 it is always the ...
The structure of nickel chromate is the same as for chromium vanadate, CrVO 4. Crystals have an orthorhombic structure with unit cell sizes a = 5.482 Å, b = 8.237 Å, c = 6.147 Å. The cell volume is 277.6 Å 3 with four formula per unit cell. [5] [7] Nickel chromate is dark in colour, unlike most other chromates which are yellow. [3]
For compounds containing an oxyanion of chromium in oxidation state of +3; For other compounds of chromium(III) as a means of distinguishing a chemical species such as hexacyanochromite(III). [Cr(CN) 6] 3− from an analogous compound in which chromium is a different oxidation state. The mineral chromite is an iron chromium oxide with empirical ...