Double salt

Double salts should not be confused with complexes. Double salts only exist in the solid. When dissolved in water, a double salt acts as a mixture of the two separate salts: it completely dissociates into simple ions while a hexaaquo complex does not; the complex ion remains unchanged. Similarly, potassium hexaiodoytterbate(II) K₄[YbI₆] is a complex salt and contains the discrete hexaiodoytterbate(II) ion [YbI₆]⁴⁻, which remains intact in aqueous solutions. In many cases, the complex ion is indicated by square brackets "[ ]". Double salts are distinct from mixed-crystal systems where two salts cocrystallise; the former involves a chemical combination with fixed composition, whereas the latter is a mixture.

In general, the properties of the double salt formed will not be the same as the properties of its component single salts.