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Bismuth Trichloride, BiCl3

Bismuth Trichloride, BiCl3, appears to have been prepared first by Boyle in 1664, and later by Poli in 1713, by heating a mixture of bismuth and mercuric chloride. It may also be obtained by the direct union of the elements; by the action of hydrochloric acid upon bismuth in the presence of air, concentrated hydrochloric acid upon bismuth trioxide, pentoxide or trisulphide, or aqua regia upon bismuth; by heating bismuth trioxide, pentoxide or trisulphide in a current of chlorine, the oxides in a current of hydrogen chloride, or bismuth with phosphorus trichloride; or by the action of silicon tetrachloride or sulphur monochloride on bismuth trioxide.

The trichloride is usually prepared by heating bismuth in a rapid current of chlorine and subliming the product in an atmosphere of carbon dioxide; by dissolving bismuth in aqua regia, evaporating the solution to dryness and distilling the residue in an atmosphere of carbon dioxide; or by dissolving bismuth trioxide in hydrochloric acid and proceeding as in the previous method.

Bismuth trichloride forms a snow-white opaque mass which can be crystallised by sublimation, the crystalline mass darkening on exposure to light. Its density is 4.75 at 20° C.; the thermal coefficient of expansion between 20° and 120° C. is approximately 167×10-6; and the molecular volume at low temperatures, calculated from the density at -194° C. and the thermal coefficient of expansion, is 64.2.

The melting point is 232° C. The density of the molten trichloride varies linearly between 250° C. and 350° C. according to the expression

D4t = 4.438 - 0.00229t

The surface tension, determined by the method of maximum bubble pressure in an atmosphere of nitrogen, and other data for the density, are as follows:

Temp., ° C.271304331353382
Density, D4t3.8113.7353.6823.6213.554
Surface Tension (dynes per cm.)66.261.858.155.352.0

The variation of the viscosity of fused bismuth trichloride with temperature is given below.

Temp., ° C.260270280290300310320330340
Viscosity×102 (grams per cm. per sec.)32.029.527.

The vapour pressure of bismuth trichloride has been determined, and the boiling point is 447° C. The heat of vaporisation is 18,000 gram-calories per mole. The vapour density (air = l) is 11.35, the calculated vapour density being 10.89.

A band spectrum of the vapour of bismuth trichloride has been observed in the region between the wavelengths 4300 A. and 5500 A. The emitter appears to be BiCl; the bands are degraded towards the longer wavelengths, and isotropic effects (due to chlorine) have been observed.

Bismuth trichloride sublimes without decomposition in an atmosphere of carbon dioxide; in air, however, a portion only sublimes unaltered, the remainder being converted into non-volatile, colourless, mica-like leaflets of bismuth oxychloride.

It will dissolve in hydrochloric acid, alcohol, acetone, liquid ammonia, and to a slight extent in liquid hydrogen sulphide. The solution in acetone behaves like an aqueous solution towards many reagents, and the solution in hydrogen sulphide does not conduct electricity.

The absorption spectrum of very dilute solutions (N/10,000) of bismuth trichloride in hydrochloric acid is characterised by a very strong selective action; a deep band with its head at λ = 3250 A. is prominent. Similar solutions of arsenic trichloride and antimony trichloride show general absorption only. The Raman spectrum of a solution of bismuth trichloride in hydrochloric acid consists of four lines, the fourth of which is exceptionally strong.

The heat of formation of the trichloride from the elements is 90,630 gram-calories per mole.

In addition to the reactions given, reduction may be carried out by passing the vapour of the trichloride over magnesium heated to the melting point; metallic bismuth is precipitated.

The trichloride is deliquescent, and is decomposed by water forming bismuth oxy chloride; with excess of water the reaction is complete, whilst it is hindered by the presence of hydrochloric acid or alkali chlorides.

No reaction takes place when bismuth trichloride is heated with sulphur monochloride or chromyl chloride.

Bismuth trichloride reacts immediately with liquid hydrogen sulphide, even at low temperatures, forming an orange-red solid, which, after drying in a desiccator over sulphuric acid, has the formula BiSCl.BiCl3.

The trichloride reacts with hydrogen sulphide in the dry way with the formation of bismuth thiochloride, BiSCl. Bismuth thiophosphate, BiPS4, is formed by the action of phosphorus pentasulphide.

When heated in nitric oxide, bismuth trichloride forms a yellow crystalline substance BiCl3.NO, which is decomposed by water. This substance can be melted in a sealed tube without decomposition, and is very hygroscopic. Bismuth trichloride also absorbs nitrogen peroxide at the ordinary temperature, forming a yellow mass of the composition BiCl3.NO2, stable in dry air. At higher temperatures this is oxidised, but it does not evolve nitrogen peroxide in vacuo. In moist air it is decomposed with evolution of nitrogen peroxide, while water converts it to bismuthyl chloride with a violent evolution of gas. Nitrosyl chloride reacts violently with bismuth trichloride at the ordinary temperature, and from the resulting solution the compound BiCl3.NOCl separates as an orange-coloured powder, which is deliquescent and decomposed by water.

The trichloride is converted into trioxide on heating with mercuric oxide. It will react with carbon compounds in a manner similar to ferric chloride; it will dissolve in many hydrocarbons, but on heating it is possibly reduced to the dichloride.

Investigation of the hydrolytic dissociation of bismuth trichloride shows that in the reaction

BiCl3 + H2O = BiOCl + 2HCl

the ratio BiCl3/[HCl]2 remains constant for a considerable range of temperature, but tends to increase somewhat at high concentrations. The presence of alkali chlorides, and more particularly alkali bromides, reduces the extent of dissociation, while alkali nitrates have a smaller influence. Sodium sulphate is practically without influence on the hydrolysis. The effect of increase of temperature is to reduce the amount of dissociation. From a study of the system Bi2O3-HCl-H2O (see tables) it appears that in certain solutions bismuthyl chloride is the stable phase, in others bismuthyl hydroxide; in the presence of alkali the solid phase BiOCl is quantitatively converted into the hydroxide BiO.OH. From measurements of the concentrations of the ions H+, Cl- and Bi3+ in hydrochloric acid solution saturated with bismuthyl chloride it has been shown that the reaction

Bi3+ + H2O + Cl-BiOCl + 2H+

obeys the law of mass action.

By dissolving bismuth trioxide in excess of hydrochloric acid and evaporating the solution, fine needle-shaped crystals of hydrated bismuth trichloride, BiCl3.2H2O, are deposited. When water is saturated with bismuth trichloride and hydrochloric acid at 20° C. and cooled to 0° C., crystals are deposited which have the composition 2BiCl3.HCl.3H2O. These crystals are stable at the ordinary temperature.

Chlorobismuthous Acid

Bismuth trichloride is very soluble in concentrated hydrochloric acid, and there are indications of the formation of a double compound; from measurements of the electrical conductivity of solutions of bismuth trichloride in aqueous hydrochloric acid the composition of this acid would appear to be either HBiCl4 or H2BiCl5, while investigations using solutions of bismuthyl chloride in hydrochloric acid (see table) indicate that H2BiCl5 predominates when excess of the acid is present in dilute solution, while HBiCl4 predominates in more concentrated solution with a lower concentration of acid.

Equilibrium in the system Bi2O3-HCl-H2O
Solubility at 18° C. (Moles per 100 moles Water).

HCl.Bi2O3.Solid Phase.

Solubility (Grams per 100 grams Saturated Solution).

At 25° CAt 30° C.
HClBi2O3.Solid Phase.HClBi2O3.Solid Phase.
35.1458.59BiCl333.8056.60BiCl3 + BiCl3.2H2O

Solubility of Bismuth chloride in hydrochloride acid at 25° C
(Gram.atoms per 1000 grams Water.)

Chlorine ContentBismuth Content.Hydrogen Content (calc.).Chlorine Content.Bismuth Content.Hydrogen Content (calc.).

The true nature of these compounds has not yet been fully ascertained. From physical investigations it is inferred that the complex may conform to one of the following two formulae:


Organic compounds corresponding to both of these have been prepared. From the examination of substituted ammonium compounds of chloro-bismuthous acid it appears possible that three types of organic compounds may exist, to which have been allotted the following names and general formulae:

  1. Hexachlorobismuthites, [NH3R]3[BiCl6];
  2. μ-Dichloro-octachloro-dibismuthites, [NHR3]4[Bi2Cl10];
  3. μ-Trichloro-hexachloro-dibismuthites, [NH3R]3[Bi2Cl9].

The elucidation of the constitution of these compounds is, however, rendered extremely difficult owing to their instability in aqueous solutions.


Bismuth trichloride forms a number of complex or double salts with alkali chlorides; some of these are described below. With lithium chloride is obtained the compound 2LiCl.BiCl3. With sodium chloride the compound NaCl.BiCl3.3H2O is formed as a deliquescent substance crystallising in needles; other sodium compounds that have been described are 2NaCl.BiCl3.2H2O and 2NaCl.BiCl3. With potassium chloride the following compounds are said to exist: 2KCl.BiCl3.2H2O, KCl.BiCl3.H2O and KCl.BiCl3.2H2O. The rubidium compounds RbCl.BiCl3.H2O and RbCl.BiCl3 have been described; also the caesium compounds 3CsCl.2BiCl3 and 3CsCl.BiCl3. With thallium chloride the compounds 3TlCl.BiCl3 and 6TlCl.BiCl3 have been obtained, both in the form of large, thin, colourless plates. Mixed halogen compounds of bismuth chloride and potassium halides have also been described, among them being KBr.KCl.BiCl3, 2KBr.BiCl3.

The following compounds with ammonium chloride have been described: The hydrate 2NH4Cl.BiCl3.2H2O forms crystals of the rhombic system, isomorphous with those of the corresponding bromide and those of the potassium double salt; the anhydrous salt forms double six-sided pyramids, and is isomorphous with the corresponding antimony compound. The compound 3NH4Cl.BiCl3 forms large, tabular crystals of the rhombic system. Another compound, to which the formula 5NH4Cl.2BiCl3 has been given, is probably formed as one of the products when a solution containing equimolecular proportions of ammonium chloride and bismuth trichloride is crystallised (the other product being 2NH4Cl.BiCl3, described above); this compound forms fine, tabular crystals of the rhombohedral system.

A systematic investigation of the compounds of bismuth trichloride with chlorides of bivalent metals revealed the following types of compounds: (1) BiCl3.M''Cl2, corresponding with the series BiCl3.2M'Cl (where M' is an alkali metal); salts of this type are regarded as derivatives of pentachlorobismuthous acid, H2[BiCl5]. The following have been examined: BiCl3.MgCl2.8H2O, stout, rectangular plates; BiCl3.BaCl2.4H2O, rhombic plates; BiCl3.CoCl2.6H2O, pale red prisms; BiCl3.NiCl2.6H2O, green needles. (2) 2BiCl3.M''Cl2, corresponding to the series BiCl3.M'Cl (where M' is an alkali metal); salts of this type are regarded as derivatives of tetrachlorobismuthous acid, H[BiCl4]. The following have been examined: 2BiCl3.CaCl2.7H2O, colourless needles; 2BiCl3.SrCl2.7H2O, stout needles; 2BiCl3.BaCl2.5H2O, slender needles. (3) 4BiCl3.M''Cl2, corresponding with the series 2BiCl3.M'Cl (where M' is an alkali metal); salts of this type are regarded as derivatives of heptachlorodibismuthous acid, H[Bi2Cl7]. The following have been examined: 4BiCl3.MgCl2.16H2O, six-sided leaflets; 4BiCl3.SrCl2.12H2O, six-sided leaflets; 4BiCl3.MnCl2.12H2O, flesh-coloured, six-sided plates; 4BiCl3.FeCl2.12H2O, faintly yellowish-red plates; 4BiCl3.CoCl2.12H2O, red, six-sided plates; 4BiCl3.NiCl2.12H2O, pale green, six-sided plates.


It has long been known that bismuth trichloride absorbs ammonia when heated gently in its presence, the reaction yielding one easily volatile addition compound, BiCl3.3NH3, and two non-volatile compounds, 2BiCl3.NH3 and BiCl3.2NH3.BiCl3.3NH3 is a colourless substance which volatilises in a current of ammonia; when acted upon by hydrogen chloride it yields the double compound 3NH4Cl.BiCl3.2BiCl3.NH3 is a red, moderately stable substance which can be melted and crystallised by solidification, but which is attacked by moisture; with hydrogen chloride it forms nearly colourless, deliquescent needles of the double compound NH4Cl.2BiCl3. The third compound, BiCl3.2NH3, is difficult to obtain pure, usually being mixed with 2BiCl3.NH3. It is a greenish-grey substance, and its composition is deduced from the fact that with hydrogen chloride it forms the compound 2NH4Cl.BiCl3.

With organic bases, bismuth trichloride forms many crystalline complexes.

Attempts to obtain a higher chloride of bismuth by the action of chlorine on molten bismuth trichloride, or by passing chlorine over a heated mixture of bismuthyl chloride and charcoal, have been unsuccessful.

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