- Crystal system: hexagonal! The rarest crystal system in my collection.
- Crystal shape: straight faceted hexagonal prism.
- Color: colorless.
- Stability on air: stable (anhydrous)
Double salt can be prepared by dissolving individual sulfates in water and crystallizing the solution:
K2SO4 + Li2SO4 = 2KLiSO4
However, the double salt does not crystallize from a stoichiometric solution, containing equal amounts of both ions. According to the literature, double salt crystallizes at room temperature, when K2SO4 : Li2SO4 mass ratio lies between 0.05 and 0.4. This corresponds to molar ratio range from 0.03 to 0.43. Thus, more than twofold excess of Li2SO4 must be present in the solution in order to crystallize the double salt.
Slow evaporation method was used. Growing is complicated by the non-stoichiometric composition of the solution. Concentration of K gradually drops as the double salt crystallizes. When it reaches the lower bound (approximately when half of the solution has evaporated), elongated crystals of lithium sulfate start growing instead; they can ruin the seed.
Potassium is not toxic, and lithium has low acute toxicity, though consumption must be avoided.
- IUPAC-NIST Solubility Data Series. 104. Lithium Sulfate and its Double Salts in Aqueous Solutions https://doi.org/10.1063/1.4977190