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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]
Ammonium dichromate is an inorganic compound with the formula (NH 4) 2 Cr 2 O 7. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting of ammonium ions and dichromate ions.
[4] Ions consisting of ... For example, an ion with a −2 charge is known as a dianion and an ion with a +2 charge is known as a dication. ... CrO 2− 4: Dichromate ...
Furthermore, the dichromate can be protonated: [HCr 2 O 7] − ⇌ [Cr 2 O 7] 2− + H +, pK a = 1.8 [6] 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 ...
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The extent of dichromatism of material can be quantified by the Kreft's dichromaticity index (DI). It is defined as the difference in hue angle (Δh ab) between the colour of the sample at the dilution, where the chroma (colour saturation) is maximal and the colour of four times more diluted (or thinner) and four times more concentrated (or thicker) sample.
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A dianion is an anion with a net charge of −2. While there exist many stable molecular dianions, such as BeF 4 2− and MgF 4 2−, [1] thus far no stable atomic dianion has been found: Electron shielding and other quantum mechanical effects tend to make the addition of another electron to an atomic anion unstable. [2]