Zinc chloride is the name of chemical compound with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white and highly soluble in water.
Anhydrous ZnCl2 can be prepared from zinc and hydrogen chloride.
Zn + 2 HCl → ZnCl2 + H2
Hydrated forms and aqueous solutions may be readily prepared similarly by treating Zn metal with hydrochloric acid. Zinc oxide and zinc sulfide react with HCl:
ZnS(s) + 2 HCl → ZnCl2(aq) + H2S(g)
Unlike many other elements, zinc essentially exists in only one oxidation state, 2+, which simplifies purification of the chloride.
Commercial samples of zinc chloride typically contain water and products from hydrolysis as impurities. Such samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, followed by heating the sublimate to 400 °C in a stream of dry nitrogen gas. Finally, the simplest method relies on treating the zinc chloride with thionyl chloride.
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