several chemical compounds consisting of two simple elements - Cr and O, - belong to a class of inorganic compounds - oxides.Their common name - chromium oxide, followed in parentheses accepted Roman numerals indicate the valence of the metal.Other names and their chemical formulas:
- chromium (II) oxide - oxide of chromium, CrO;
- chromium (III) oxide - chrome greens, sesquioxide of chromium, Cr2O3;
- chromium (IV) oxide - chromic oxide, CrO2;
- chromium (VI) oxide - chromic anhydride, chromium trioxide, CrO3.
compound wherein shestivalenten metal and chromium oxide is the highest.This solid odorless, appearance is a dark-red crystals (they are spread out in the air because of the strong hygroscopic).Molar weight - 99.99 g / mol.Density at 20 ° C is equal to 2.70 g / cc.Melting point - 197 ° C, boiling point - 251 ° C.At 0 ° C, soluble in water 61.7 g / 100 at 25 ° C - 63 g / 100 ml at 100 ° C - 67.45 g / 100 ml.The oxide is also dissolved in sulfuric acid (chromic this mixture, which was used in the laboratory for chemical washing of dishes) and nitric acid, ethanol, ethyl ether, acetic acid, acetone.At 450 ° C decomposes to Cr2O3.
chromium (VI) oxide is used in the electrolysis process (for pure chromium) for chromate galvanized products, electrolytic plating, as a strong oxidizing agent (for the production of indigo and isatin).Higher chromium oxide is used for detecting alcohol in exhaled air.The reaction proceeds according to the scheme: 4CrO3 + 6H2SO4 + 3C2H5OH → 2Cr2 (SO4) 3 + 3CH3COOH + 9H2O.The presence of alcohol indicates a change in color of the solution (turns green).
Chromium (VI) oxide, as well as all hexavalent Cr, is a potent poison (lethal dose - 0.1 g).Because of its high activity CrO3 causes ignition (with explosions) organic materials in contact with them.Despite the low volatility, higher chromium oxide is dangerous if inhaled, because it causes lung cancer.Upon contact with the skin (even if it is removed soon) cause irritation, dermatitis, eczema, stimulates the development of cancer.
Oxide with tetravalent chromium CrO2 appearance is a solid in the form of ferromagnetic iron tetrahedral crystals.Chromium oxide 4 has a molar mass of 83.9949 g / mol, a density of 4.89 g / cc.The substance melts simultaneously decomposing, at a temperature of 375 ° C.Insoluble in water.It used in magnetic recording media as the working substance.With the popularity of CD-ROMs and DVD-ROM drive to use chromium (IV) oxide decreased.It was first synthesized in 1956 by a chemist from EI DuPont company Norman L. Cox by decomposition of chromium trioxide in the presence of water at a temperature of 640 ° C and a pressure of 200 MPa.DuPont is manufactured under license in Japan by Sony and BASF in Germany.
chromium oxide Cr2O3 3 is a solid fine crystalline substance from light to dark green.The molar mass equal to 151.99 g / mol.Density - 5.22 g / cc.Melting point - 2435 ° C, boiling - 4000 ° C.The refractive index of the pure substance - 2,551.This oxide is not soluble in water, alcohol, acetone, acid.As it approaches the density of the density of corundum, it is administered in formulations polishing agents (eg toothpaste GOI).This is one of the basic oxides of chromium, which is used as a pigment.By first secret technology it was received in 1838 as a clear, hydrated forms.In nature, found in the form of chromium iron ore FeO • Cr2O3.
Oxide bivalent chromium - solid black or red color with a melting point of 1550 ° C.Melts with decomposition.Molar mass - 67.996 g / mol.Chromium oxide (II) of red color is not pyrophoric, and the same substance is a black pyrophoric.The powder ignites spontaneously in air, so it can be kept only under a layer of water, as it does not interact.Black chromium oxide to obtain in its pure form is very difficult.For
oxide with lower valence chromium typical basic properties and for the oxide with the higher valence - acid.
