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Chromium is a chemical element; ... The name of the element is derived from the Greek word χρῶμα, ... (PbCrO 4 ·Pb(OH) 2). A very important chromate pigment ...
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 are rare, but do nevertheless occasionally exist.
In acid solution the aquated Cr 3+ ion is produced. Cr 2 O 2− 7 + 14 H + + 6 e − → 2 Cr 3+ + 7 H 2 O ε 0 = 1.33 V. In alkaline solution chromium(III) hydroxide is produced. The redox potential shows that chromates are weaker oxidizing agent in alkaline solution than in acid solution. [6] CrO 2− 4 + 4 H 2 O + 3 e − → Cr(OH) 3 + 5 OH −
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. It is a crystalline ionic solid with a very bright, red-orange color.
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+
This process involves atomic chromium as an intermediate, and occurs in two steps. The hydrogenation (step 2) is a spontaneous process. Cr (s) → Cr (g) Cr (g) + H 2 (g) → HCr(μ-H) 2 CrH (g) In an inert gas matrix atomic Cr reacts with H 2 to make the dihydride when it is irradiated with ultraviolet light between 320 and 380 nm. [2]
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It is derived from the mineral chromite, (Fe,Mg)Cr 2 O 4. The conversion of chromite to chromia proceeds via Na 2 Cr 2 O 7, which is reduced with sulfur at high temperatures: [7] Na 2 Cr 2 O 7 + S → Na 2 SO 4 + Cr 2 O 3. The oxide is also formed by the decomposition of chromium salts such as chromium nitrate, or by the exothermic ...