Chemical elements
  Chromium
    Isotopes
    Energy
    Occurrence
    Preparation
    Physical Properties
    Chemical Properties
    Alloys
    Amalgams
    Compounds
      Chromous Fluoride
      Chromic Fluoride
      Chromyl Fluoride
      Chromous Chloride
      Chromic Chloride
      Oxychlorides
      Chromyl Chloride
      Trichromyl Chloride
      Chromium Chlorate
      Chromium Perchlorate
      Chromous Bromide
      Chromic Bromide
      Complex Halogen-halides
      Chromous Iodide
      Chromic Iodide
      Chromium Iodate
      Chromous Oxide
      Chromo-chromic Oxides
      Chromic Oxide
      Chromic Hydroxide
      Barium Chromite
      Cadmium Chromite
      Calcium Chromite
      Cobalt Chromite
      Cupric Chromite
      Cuprous Chromite
      Ferrous Chromite
      Lithium Chromite
      Magnesium Chromite
      Manganese Chromite
      Zinc Chromite
      Chromium Dioxide
      Chromium Trioxide
      Aluminium Chromate
      Ammonium Chromate
      Ammonium Lithium Chromate
      Ammonium Potassium Chromate
      Ammonium Sodium Chromate
      Ammonium Dichromate
      Ammonium Fluochromate
      Barium Chromate
      Barium Dichromate
      Barium Potassium Trichromate
      Beryllium Chromate
      Bismuth Chromate
      Bismuth Potassium Chromates
      Cadmium Chromate
      Cadmium Dichromate
      Cadmium Trichromate
      Caesium Chromate
      Caesium Dichromate
      Calcium Chromate
      Calcium Dichromate
      Cobalt Chromate
      Cobalt Dichromate
      Copper Chromates
      Cupric Dichromate
      Gold Chromates
      Iron Chromates
      Ferric Chromate
      Ferric Ammonium Chromate
      Lead Chromate
      Basic Lead Chromates
      Lead Dichromate
      Lithium Chromate
      Lithium Chlorochromate
      Magnesium Chromates
      Manganese Chromates
      Mercuric Chromate
      Mercuric Dichromate
      Nickel Chromate
      Nickel Dichromate
      Potassium Chromate
      Potassium Dichromate
      Potassium Trichromate
      Potassium Tetrachromate
      Potassium Fluochromate
      Potassium Chlorochromate
      Rubidium Dichromate
      Silver Chromate
      Silver Dichromate
      Sodium Chromate
      Sodium Dichromate
      Sodium Trichromate
      Sodium Chlorochromate
      Stannic Chromate
      Strontium Chromate
      Strontium Dichromate
      Strontium Trichromate
      Thallous Chromate
      Thallic Chromate
      Thallous Dichromate
      Thallous Trichromate
      Thallous Chlorochromate
      Uranyl Chromate
      Zinc Chromate
      Zinc Dichromate
      Zinc Trichromate
      Perchromic Acid
      Chromium Tetroxide Triammine
      Chromous Sulphide
      Chromium Tetrasulphide
      Chromic Sulphide
      Sodium Thiochromite
      Potassium Thiodichromite
      Chromic Sulphite
      Chromous Sulphate
      Chromic Sulphate
      Lithium Chromic Sulphate
      Sodium Chromic Sulphates
      Potassium Chromic Sulphates
      Potassium Chromium Alum
      Ammonium Chromium Alum
      Hydrazine Chromium Alum
      Sulphochromic Acid
      Chromous Selenide
      Chromic Selenide
      Chromic Selenite
      Chromium Nitrides
      Chromium Azide
      Chromic Nitrate
      Chromium Monophosphide
      Chromium Sesquiphosphide
      Chromic Hypophosphite
      Chromous Orthophosphate
      Chromic Orthophosphates
      Chromous Metaphosphate
      Chromic Metaphosphate
      Chromic Pyrophosphate
      Ammonium Chromi-pyrophosphate
      Potassium Chromi-pyrophosphate
      Sodium Chromi-pyrophosphate
      Chromous Thiophosphite
      Chromous Thiopyrophosphite
      Chromous Thiopyrophosphate
      Chromous Arsenide
      Chromium Sesqui-arsenide
      Chromic Arsenite
      Chromic Arsenate
      Chromium Pyroarsenate
      Chromic Thioarsenite
      Chromium Chlorantimonate
      Chromium Orthoantimonichloride
      Tetrachromium Carbide
      Pentachromium Dicarbide
      Tetrachromium Dicarbide
      Chromium Tungsten Carbide
      Chromous Carbonate
      Ammonium Chromous Carbonate
      Potassium Chromous Carbonate
      Sodium Chromous Carbonate
      Chromic Carbonates
      Chromium Thiocarbonate
      Chromous Cyanide
      Chromic Cyanide
      Potassium Chromocyanide
      Hydrogen Chromicyanide
      Ammonium Chromicyanide
      Lithium Chromicyanide
      Sodium Chromicyanide
      Potassium Chromicyanide
      Cobaltous Chromicyanide
      Cupric Chromicyanide
      Lead Chromicyanide
      Manganous Chromicyanide
      Mercury Chromicyanide
      Nickel Chromicyanide
      Silver Chromicyanide
      Zinc Chromicyanide
      Chromous Thiocyanate
      Chromic Thiocyanate
      Chromithiocyanic Acid
      Ammonium Chromithiocyanate
      Sodium Chromithiocyanate
      Potassium Chromithiocyanate
      Barium Chromithiocyanate
      Silver Chromithiocyanate
      Lead Chromithiocyanate
      Chromium Ferrocyanide
      Trichromium Silicide
      Dichromium Silicide
      Trichromium Disilicide
      Chromium Disilicide
      Chromium Aluminium Silicide
      Sodium Chromisilicates
      Chromium Silicofluoride
      Chromium Boride
      Trichromium Diboride
      Chromous Borate
      Chromic Borate
    Detection
    Estimation
    PDB 1huo-9icc

Chromic Chloride, CrCl3






Chromic Chloride, CrCl3 may be obtained by a variety of methods, for example,
  1. by heating metallic chromium at 600° C. in a stream of chlorine;
  2. by passing a stream of chlorine over chromium sesquioxide at 440° C.;
  3. by heating a mixture of the sesquioxide and carbon in a stream of chlorine;
  4. by the action of a mixture of carbon monoxide and chlorine on chromium sesquioxide at a red heat:

    Cr2O3 + 3CO + 3Cl2 = 2CrCl3 + 3CO2;
  5. by the interaction of phosphorus trichloride and chromyl chloride, CrO2Cl2; or of chromyl chloride, carbon monoxide, and chlorine.
  6. Undoubtedly the most convenient method is that of Bourion, who finds that sulphur chloride alone is preferable to a mixture of that substance with chlorine for the chlorination of the oxide. Precipitated calcined chromic oxide is attacked by sulphur chloride at a temperature rather above 400° C., but below red heat:

    6S2Cl2 + 2Cr2O3 = 4CrCl3 + 3SO2 + 9S.
Modifications of the foregoing and other methods have been suggested.

Anhydrous chromic chloride forms large, lustrous, unctuous plates of the colour of peach blossom, of density 2.757 at 15° C. It has a specific heat of 0.143. Its vapour density just above 1065° C., at which temperature it volatilises, is 6.135 (air = 1), whilst at 1200° C. it approximates to the theoretical value, 5.478, required by the formula CrCl3. At much higher temperatures partial decomposition takes place, with consequent diminution of the vapour density.

Chromic chloride is reduced at a red heat by hydrogen to chromous chloride, and by zinc or magnesium to metallic chromium. Heated in air, green chromium sesquioxide is formed; in oxygen or moist chlorine, chromyl chloride is produced. On strongly heating in dry ammonia, the nitride, CrN, is obtained, whilst in presence of ammonium chloride, the lower chloride is formed; in hydrogen sulphide, the black crystalline sesquisulphide Cr2S3, and with phosphorous pentachloride, the double chloride 2CrCl3.PCl5, are produced. Mineral acids, including even aqua regia, have no action on the anhydrous salt; fused alkali hydroxide or carbonate, in presence of nitrate, yields alkali chromate and chloride. Anhydrous chromic chloride is almost insoluble in cold water, but dissolves readily in presence of very slight traces (0.00001 per cent.) of chromous chloride, either previously added or formed in solution by the addition of a reducing agent such as tin, zinc, ferrous or cuprous chlorides. It has not been proved that the catalytic influence of these reagents is wholly due to the formation of chromous chloride. Chromic chloride is sparingly soluble in boiling water.

A solution of chromic chloride is readily obtained by the action of dilute hydrochloric acid on chromic hydroxide, or on chromium sesquioxide which has not been ignited; this solution on evaporation yields an amorphous, deliquescent, green mass, soluble in water and in alcohol. The product on heating in hydrogen chloride or chlorine at temperatures above 250° C. becomes anhydrous, at the same time assuming the usual colour of the anhydrous salt. Basic chlorides are formed by heating the hydrated chloride in air. A number of hydrates, one at least appearing to exist in three isomeric forms, have been prepared. The hydrates in solution all yield the same hydroxide, Cr(OH)3, on treatment with an alkali hydroxide.

Dilute solutions of the chloride are violet in colour, while more concentrated or acidulated solutions are green, the colour depending on the equilibrium established between the green and violet modifications of the salt which is in solution as the hexahydrate, CrCl3.6H2O. The amount of the green salt present at equilibrium increases with concentration. The violet modification is precipitated before the green when hydrogen chloride is passed into a boiled solution of the mixture. From dehydration experiments Werner concluded that the molecule of the green hydrate contained 4H2O as water of constitution and 2H2O as water of crystallisation, while the violet modification contained 6H2O as water of constitution. Olie confirmed these results at ordinary temperatures, but found that at 100° C. both varieties lost approximately 4H2O. Further, Werner found that from solutions of the violet hydrate, the whole, and from solutions of the green hydrate only one- third, of the chlorine could be precipitated by a soluble silver salt. Although the amount of chlorine precipitated appears to depend to a certain extent on the conditions of the experiment, yet it is evident that in the two salts the chlorine is not all similarly combined. The isomerism was explained by Werner according to the co-ordination theory, and the violet and green chlorides were considered to possess the formulae [Cr(H2O)6]Cl3 and | CrCl2(H2O)4]Cl.(H2O)2 respectively, the former being termed the hexaquo salt and the latter dichlortetraquo- chromic chloride, or simply dichlorchromium chloride.

It has been suggested that the greyish-blue or violet chromic chloride is bimolecular, 2[Cr(H2O)6Cl3], while the green variety is uni- molecular. This is not accepted by Bjerrum, who considered that, in order to interpret the equilibrium changes of a concentrated solution of chromic chloride, it was necessary to assume the presence of a third isomeric hexahydrate in the solution. This he succeeded in isolating, as very deliquescent pale green crystals, by adding ether saturated with hydrogen chloride to the solution remaining after precipitating the violet salt with hydrogen chloride. Two-thirds of the chlorine present in this compound may be precipitated by means of silver nitrate, so that it may be regarded as monochlorpentaquochromic chloride, [CrCl (H2O)5]Cl2.H2O.

In dilute solution the dark green hexahydrate changes rapidly to the light green salt, and then more slowly to the violet salt, thus:

[CrCl2(H2O)4]Cl.(H2O)2, dark green, → [CrCl(H2O)5]Cl2.H2O, light green, → [Cr(H2O)6]Cl3, violet.

The influence of light and of the presence of neutral chlorides on the transformation has been studied.

By dehydration of the green hydrate, Bjerrum obtained two red substances, 2CrCl3.3H2O and 2CrCl3.H2O. Other hydrates are the deca- hydrate, CrCl3.10H2O, and tetrahydrate, CrCl3.4H2O. The former yields brilliant green triclinic crystals, strongly dichroic, and can be obtained by triturating the hexahydrate with the calculated amount of water. Werner and Gubser assign the formula



to the decahydrate, which in dry air loses water, being converted first into the hexahydrate and finally into the tetrahydrate, a pale green, slightly hygroscopic powder. A hydrate, 2CrCl3.9H2O, has also been said to exist. An alcoholate, CrCl3.3C2H5OH, in the form of red needles, stable in dry air, has been obtained by the action of dry hydrogen chloride in absolute alcohol upon metallic chromium. Double salts with alkali chlorides, with antimony pentachloride, with organic bases, ammonia (for example, 2CrCl3.12NH3.2H2O and 2CrCl3.10NH3), and substituted ammonias are known. Complex halogen-halides and chlorsulphates have also been obtained.

On progressive hydrolysis, chromic chloride gives rise to two soluble basic chlorides, Cr(OH)Cl2 and Cr(OH)2Cl, and an insoluble grey-green hydroxide. The compound, Cr(OH)2Cl, is never present in any large proportion, and the hydroxide is only formed upon addition of alkali. The formulae of the three compounds are probably [Cr(H2O)5(OH)]Cl2, [Cr(H2O)4(OH)2]Cl, and Cr(H2O)3(OH)3 respectively.


© Copyright 2008-2012 by atomistry.com