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Sodium dichromate is the inorganic compound with the formula Na 2 Cr 2 O 7.However, the salt is usually handled as its dihydrate Na 2 Cr 2 O 7 ·2H 2 O.Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compounds and materials based on chromium are prepared from this salt. [1]
Hexavalent chromium occurs only rarely in nature, an exception being crocoite (PbCrO 4). [3] It is however produced on a large scale industrially. Virtually all chromium ore is processed via the formation of hexavalent chromium, specifically the salt sodium dichromate. [2]
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 ...
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:
The formulations typically contain hexavalent chromium compounds, such as chromates and dichromates. [4] The widely used Cronak process for zinc and cadmium consists of 5–10 seconds of immersion in a room-temperature solution consisting of 182 g/L sodium dichromate (Na 2 Cr 2 O 7 · 2H 2 O) and 6 mL/L concentrated sulfuric acid. [5]
Hexavalent chromium compounds (including chromium trioxide, chromic acids, chromates, chlorochromates) are toxic and carcinogenic. Chromium trioxide and chromic acids are strong oxidizers and may react violently if mixed with easily oxidizable organic substances. Chromic acid burns are treated with a dilute sodium thiosulfate solution. [18]
For lab and small scale preparations a mixture of chromite ore, sodium hydroxide and sodium nitrate reacting at lower temperatures may be used (even 350 C in the corresponding potassium chromate system). [2] Subsequent to its formation, the chromate salt is converted to sodium dichromate, the precursor to most chromium compounds and materials. [3]
Chromium(III) chloride (also called chromic chloride) is an inorganic chemical compound with the chemical formula Cr Cl 3. It forms several hydrates with the formula CrCl 3 · n H 2 O , among which are hydrates where n can be 5 (chromium(III) chloride pentahydrate CrCl 3 ·5H 2 O ) or 6 (chromium(III) chloride hexahydrate CrCl 3 ·6H 2 O ).
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