Many combinations of mono and trivalent cations yield crystals of the same stoichiometry and structure. The crystals are normally in the form of an octahedron. Sodium, potassium and ammonium ions are often the monovalent species whereas aluminum and chromium are examples of the trivalent ions. Potassium alum, KAl(SO4)2 12H2O, is the most common and is used in water purification, paper manufacturing and as a mordant in dyeing. In this experiment we will perform a series of chemical reactions which lead to the synthesis of the ionic compound potassium alum.