Doppelsalz

Doppelsalz, also known as double salt, is a salt that is formed from two different cations and one anion, or two different anions and one cation, or two different cations and two different anions. In essence, it is a stoichiometric combination of two or more simple salts that crystallizes together as a single compound. The constituent ions are present in the same ratio as they are in the individual simple salts. Doppelsalze do not dissociate into their constituent ions when dissolved in water, but rather into the ions of the double salt itself. This distinguishes them from mixtures of salts, where each salt would dissociate independently. Common examples of doppelsalze include potassium alum (KAl(SO₄)₂·12H₂O), which is a combination of potassium sulfate and aluminum sulfate, and carnallite (KMgCl₃·6H₂O), formed from potassium chloride and magnesium chloride. The crystalline structure of a doppelsalz is distinct from the structures of its individual component salts. Their formation and properties are often studied in the field of inorganic chemistry.