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Chromium(III) oxide is amphoteric. Although insoluble in water, it reacts with acid to produce salts of hydrated chromium ions such as [Cr(H 2 O) 6] 3+. [10] It is also attacked by concentrated alkali to yield salts of [Cr(OH) 6] 3−. When heated with finely divided carbon or aluminium, it is reduced to chromium metal: Cr 2 O 3 + 2 Al → 2 Cr ...
A large number of chromium(III) compounds are known, such as chromium(III) nitrate, chromium(III) acetate, and chromium(III) oxide. [8] Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid, but it can also be formed through the reduction of chromium(VI) by cytochrome c7. [9] The Cr 3+
Chromium(III) nitrate describes several inorganic compounds consisting of chromium, nitrate and varying amounts of water. Most common is the dark violet hygroscopic solid. An anhydrous green form is also known. Chromium(III) nitrate compounds are of a limited commercial importance, finding some applications in the dyeing industry. [2]
Chromium aventurine, in which aventurescence is achieved by growth of large parallel chromium(III) oxide plates during cooling, is made from glass with added chromium oxide in amount above its solubility limit in glass. Cadmium together with sulphur forms cadmium sulfide and results in deep yellow color, often used in glazes. However, cadmium ...
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:
Chromium(IV) oxide is used to manufacture magnetic tape used in high-performance audio tape and standard audio cassettes. [89] Chromium(III) oxide (Cr 2 O 3) is a metal polish known as green rouge. [90] [91] Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds. [92]
As hexavalent chromium compounds are prohibited for use in the EU based on ROHS regulations and are toxic and carcinogenic, solutions based on molybdate are proposed as a replacement (e.g. molybdate 30-100g/ boric acid 10-18 g/manganese sulfate 0.5 g /1 liter of water, 0.1 - 20 A/dm2, 0.1–15 minutes).
According to Gettens, especially when mixed with organic colors, it can take on a green tone. This effect is attributed to reduction of some chromate to chromium(III) oxide. [6] Owing to its high lead content, the pigment is prone to discoloration over time, particularly in the presence of sulfur compounds.