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Chromium(III) hydroxide is a gelatinous green inorganic compound with the chemical formula Cr(OH) 3. It is a polymer with an undefined structure and low solubility. It is amphoteric, dissolving in both strong alkalis and strong acids. [2] In alkali: Cr(OH) 3 + OH − → CrO − 2 + 2 H 2 O In acid: Cr(OH) 3 (OH 2) 3 + 3 H + → Cr(OH 2) 6 3+
The Pourbaix diagram for chromium in pure water, perchloric acid, or sodium hydroxide [1] [2] Chromium compounds are compounds containing the element chromium (Cr). Chromium is a member of group 6 of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium ...
An amphiprotic molecule (or ion) can either donate or accept a proton, thus acting either as an acid or a base. Water , amino acids , hydrogencarbonate ion (or bicarbonate ion) HCO − 3 , dihydrogen phosphate ion H 2 PO − 4 , and hydrogensulfate ion (or bisulfate ion) HSO − 4 are common examples of amphiprotic species.
Chromium(III) hydroxide (Cr(OH) 3) is amphoteric, dissolving in acidic solutions to form [Cr(H 2 O) 6] 3+, and in basic solutions to form [Cr(OH) 6] 3−. It is dehydrated by heating to form the green chromium(III) oxide (Cr 2 O 3), a stable oxide with a crystal structure identical to that of corundum. [21]
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The primary chromium ore is the mixed metal oxide chromite, FeCr 2 O 4, found as brittle metallic black crystals or granules. Chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms iron(III) oxide, Fe 2 O 3:
A variety of other chromium(III) sulfates are known, but also contain hydroxide or oxide ligands. Most important commercially is basic chromium sulfate, which is thought to be [Cr 2 (H 2 O) 6 (OH) 4]SO 4 (CAS#39380-78-4). [2] It results from the partial neutralization of the hexahydrates. Other chromium(III) hydroxides have been reported. [3]
Similarly, when ammonia is the solvent, the strongest acid is ammonium (NH 4 +), thus HCl and a super acid exert the same acidifying effect. The same argument applies to bases. In water, OH − is the strongest base. Thus, even though sodium amide (NaNH 2) is an exceptional base (pK a of NH 3 ~ 33), in water it