Strontium Bromide, SrBr₂

Strontium Bromide, SrBr₂, may be obtained by dissolving the oxide, carbonate, or sulphide in hydrobromic acid, evaporating to dryness, and heating the residue in a current of the gaseous acid. A gelatinous strontium bromide has also been obtained.

The heat of formation of strontium bromide from its elements is 176.5 Cal.

It is a colourless salt, melting without decomposition at 643° C., and volatilising at 770° C. It can be heated to dryness in a platinum dish over a free flame without the slightest loss of halogen.

The salt dried at 200° C. has a density of 4.216 at 24° C.

The fused salt is less hygroscopic than the powdered.

Strontium bromide is readily soluble in water, the heat of solution Being 16.1 Cal.

Densities of strontium bromide solutions, vapour pressures, freezing-points, electrical conductivities, and refractive indices, have been determined.

The existence of two hydrates, the hexa- and the mono-hydrate, has been definitely established, but there is probably also a dihydrate, and Thomsen considered that calorimetric determinations indicated the existence of four hydrates, with 1, 2, 5, and 6 molecules of water of crystallisation respectively.

The experiments of Rammelsberg first indicated the existence of Strontium Bromide Hexahydrate, SrBr₂.6H₂O, isomorphous with the chloride hexahydrate. It is hygroscopic, and melts at 100° C. in its own water of crystallisation. The vapour pressure of the salt at 20° C. is 1.8 mm. The heat of hydration is 23.33 Cal., and the heat of solution of the hydrate -7.22 Cal. The density is 2.358.

According to Richards and Yngve, transition from the hexahydrate to the dihydrate takes place at 88.62° C. The heat of hydration to the Strontium Bromide Dihydrate, SrBr₂.2H₂O, is 9.95 Cal., and the heat of solution 6.16 Cal.

The hexahydrate loses 5 molecules of water in the desiccator, or at 100° C. in air, giving the Strontium Bromide Monohydrate, SrBr₂.H₂O. The heat of hydration is 6.15 Cal., and the heat of solution 9.96 Cal.

With ammonia strontium bromide forms the compound SrBr₂.8NH₃, SrBr₂.2NH₃, and SrBr₂.NH₃, which have a dissociation pressure of 100 mm. at the temperatures 30°, 68°, and 146° C. respectively, and the heats of formation 10.9, 12.8, and 16.2 Cal. There is also evidence of the existence of a labile isomeride of the di- ammoniate with a pressure of 143 mm. at 63° C. The anhydrous salt is soluble in ethyl alcohol, and from the solution the compound 2SrBr₂.5C₂H₅OH crystallises out in large orthorhombic prisms. An addition compound with glycine, SrBr₂.2NH₂CH₂COOH.3H₂O, has also been obtained.

Strontium bromide forms double salts with mercuric bromide, 2HgBr₂.SrBr₂, and SrBr₂.HgBr₂, and with mercuric cyanide, 2Hg(CN)₂.SrBr₂.6H₂O. Freezing-point curves of mixtures of strontium bromide with bromides of the alkali metals, indicate the existence of the compounds 2SrBr₂.LiBr, SrBr₂.2KBr, and 2SrBr₂.KBr.