In solid form, a double salt creates its own unique crystal structure. This lattice often traps water molecules inside it. Because of this new structure, the solid has different physical properties than either original salt alone.
But this unique identity vanishes when you add water. In a solution, a double salt acts exactly like a simple mix of its starting salts. It releases all the same basic ions into the water.
The water molecules pull the crystal apart completely. No new bonded groups stay together. This complete breakup is the main difference between double salts and complex salts.
Complex salts contain a central metal bonded to other groups. These complex groups stay joined together even in water. Students often confuse double salts with simple mixtures.
A simple mixture can have any random amount of each salt. A double salt always forms with an exact, repeating chemical recipe. The crystal shape of a double salt looks different from its parent salts.
You cannot separate the two parts by physical means like sorting. You must dissolve them or melt them to break the chemical bond.