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Beryllium Chloride, BeCl2

Beryllium chloride, BeCl2, has played an important part in the history of beryllium. It was the first source of the metal, and the discovery that its vapour density between 490° and 1520° C. corresponded to the formula BeCl2, was fundamental for the discussion over the valency and atomic weight of the element. The formula has been confirmed by the molecular weight of beryllium chloride in pyridine.

Anhydrous beryllium chloride is a white crystalline solid, of density 1.8995 at 25° C., which melts at about 440° C. and boils at about. 520° C. The fused chloride is a non-conductor. It decomposes when heated in the presence of air, but volatilises without decomposition if water and air are absent.

It dissolves violently in water with loss of hydrogen chloride. With ether it forms a compound, BeCl2.2H2O, and dissolves readily in alcohol but not in chloroform, carbon tetrachloride, benzene, or sulphur dichloride. The tetrahydrate can be obtained by treatment with hydrogen chloride and ether: alcohol can replace the ether in preparing it. Anhydrous beryllium chloride forms compounds with many organic bases.

Beryllium chloride is easily prepared in solution by dissolving the oxide or hydroxide in hydrochloric acid. When such a solution is evaporated down hydrogen chloride passes off and a gummy basic mass is left. The pure chloride can only be prepared by methods which exclude the presence of water.

Anhydrous beryllium chloride has been prepared by five principal methods. A very pure product was obtained by the action of hydrogen chloride gas on the metal. It has also been prepared by the action of carbon tetrachloride on red-hot beryllia, by passing chlorine and sulphur chloride vapour over the heated oxide, and by the action of chlorine or hydrogen chloride on the heated carbide. Most workers heated a mixture of beryllium oxide and carbon in a current of chlorine. Mieleitner and Steinmetz say that hydrous beryllium chloride, like the compound BeCl2.4H2O, cannot be completely dehydrated by heating in dry hydrogen chloride or chlorine.

The sublimed chloride forms a tetra-ammoniate, BeCl2.4NH4, with dry ammonia. If the mixture becomes hot the composition of the compound approximates to BeCl2.2NH4.

Some experimenters have noted an action of beryllium chloride upon glass, but Parsons doubts whether it has any action on Jena or hard potash glass. A thin film of oxide, produced by traces of moisture, might be mistaken for corrosion.

The following thermochemical data have been given for beryllium chloride: -

[Be] + (2HCl) = [BeCl2] + (H2)+121.1 Cal.

[Be] + (Cl2) = [BeCl2] + 155 Cal.

[BeCl2]+Aq. = BeCl2.Aq.+44.5 Cal.

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