Strontium chloride

Strontium chloride (SrCl2) is a salt of strontium and chloride. It is a 'typical' salt, forming neutral aqueous solutions. As with all compounds of strontium, this salt emits a bright red colour in flame, and is commonly used in fireworks to that effect. Its properties are intermediate between those for barium chloride, which is more toxic, and calcium chloride. Strontium chloride can be prepared by treating aqueous strontium hydroxide or strontium carbonate with hydrochloric acid: Crystallization from cold aqueous solution gives the hexahydrate, SrCl2·6H2O. Dehydration of this salt occurs in stages, commencing above . Full dehydration occurs at . In the solid state, SrCl2 adopts a fluorite structure. In the vapour phase the SrCl2 molecule is non-linear with a Cl-Sr-Cl angle of approximately 130°. This is an exception to VSEPR theory which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarisation of the electron core of the strontium atom causes a distortion of the core electron density that interacts with the Sr-Cl bonds. Strontium chloride is a precursor to other compounds of strontium, such as yellow strontium chromate, strontium carbonate, and strontium sulfate. Exposure of aqueous solutions of strontium chloride to the sodium salt of the desired anion often leads to formation of the solid precipitate: SrCl2 + Na2CrO4 → SrCrO4 + 2 NaCl SrCl2 + Na2CO3 → SrCO3 + 2 NaCl SrCl2 + Na2SO4 → SrSO4 + 2 NaCl Strontium chloride is often used as a red colouring agent in pyrotechnics. It imparts a much more intense red colour to the flames than most alternatives. It is employed in small quantities in glass-making and metallurgy. The radioactive isotope strontium-89, used for the treatment of bone cancer, is usually administered in the form of strontium chloride. Seawater aquaria require small amounts of strontium chloride, which is consumed during the growth of certain plankton.