students Logo
Home | Sitemap | Contact us | Search | Language
Select Your Theme
Left Home Right
  Home >> Chemistry Dictionary >> Chrome Platting Chromium Oxides

Chrome.
Having a chromium plated surface.
Chrome alum,
KCr(SO4)2 12H2O. A typical alum used as a gelatin hardener.
Chrome plating.
A coating of metals and various articles with chromium to prevent corrosion.
Chromic.
Outdate nomenclature for chromium (III) compounds.
Chromite
FeCr2O4Brownish-black mineral with the spinel structure used as a source of Cr and its compounds.

Chromium.
Symbol Cr. A hard silvery transition element; 24; r.a.m. 52.00; r.d. 7.19; m.p. 1900°C; b.p. 2640°C. The main ore is chromite (FeCr7O4). The metal is extracted by heating chromite with sodium chromate, from which chromium can be obtained by electrolysis. Alternatively, chromite can be heated with carbon in an electric furnace to give ferrochrome, which is used in making alloy steels. The metal is also used as a shiny decorative electroplated coating and in the manufacture of certain chromium compounds.
At normal temperature the metal is corrosion-resistant.
           

It reacts with dilute hydrochloric and sulphuric acids to give chromium (II) salts. These readily oxidize to the more stable chromium (III) salts Chromium also forms compounds with the +6 oxidation state, as in chromates, which contain the CrO42- ion. The element was discovered in 1797 by Vauguelin.
Chromium.(II)
Oxide A black insoluble powder, CrO. Chromium (II) oxide is prepared by oxidizing chromium amalgam with air. At high temperatures hydrogen reduces it to the metal.

Chromium (III)
Oxide A green crystalline water-insoluble salt, Cr2O3; r.d. 5.21; m.p. 2266°C; b.p. 4000°C. It is obtained by heating chromium in a stream of oxygen or by heating ammonium dichromate. The industrial preparation is by reduction of sodium dichromate with carbon Chromium (III) oxide is amphoteric, dissolving in acid to give chromium (III) ions and in concentrated solutions of alkali to give chromites. It is used as a green pigment in glass, porcelain, and oil paint.

Chromium (IV)
Oxide (chromium dioxide) A black insoluble powder, CrO2; m.p. 300°C. It is prepared by the action of oxygen on chromium (VI) oxide or chromium (III) oxide at 420-450°C and 200-300 atmospheres. The compound is unstable.
Chromium(VI)
Oxide, (Chromium Triozide, Chromic Anhydride, CrO3) A real crystalline solid is prepared by the action of concentrated sulphuric acid on potassium dichromate.
It is used as an oxidizing agent, in volumetric analysis and disinfectant with glacial acetic acid.

Chromium Hydroxide.
It seems unlikely that a true chromium (III) hydroxide exists but hydroxy complexes, e.g. (Cr(H2O)5OH]2+, [(H2O)4Cr(µ-OH)2 Cr(H2O)4]4+, are formed by addition of base to aquo-complexs and polymeric species and ultimately gels are formed by addition of further base.
Chromium oxides.
Chromium trioxide, CrO3. Red precipitate from [CrO4]2- plus conc. H2SO4, m.p 198°C loss oxygen at 420°C. CrO3 is a powerful oxidizing agent and is used such. Acidic gives [CrO4]2- with water.
Chromium dioxide. CrO2 (H2O plus O2 on CrO3 at high temperature) Black solid with the structure forming chromates (IV) in solid state reactions. Used in magnetic taps.
Chromium (III) oxide. Cr2O3 (heat on (NH2)2Cr2O7, hydrolysis and ignition of chromium (III) compounds).
Green compound with the corundum structure. Gives chromates (III) in solid state reactions, anionic species with hydroxyl ions and [Cr(H2O)6]3+ with acids. Used as a green pigment (viridian) and to give green colours in glass and porcelain.

           
Left Home Right
Home | Sitemap | Terms | Privacy Policy | Contact us |
  Language >> English | Franįais | Espaņol | Deutsch | Italiano | Portugues | Japanese | Korean | Sim-Chinese