NaAlSO4212H2O

Sodium aluminum sulfate dodecahydrate, with the chemical formula NaAl(SO4)2·12H2O, is a member of the alum family of double sulfates. It is the sodium analogue of potassium alum (KAl(SO4)2·12H2O) and is sometimes referred to as sodium alum or sodium aluminum sulfate dodecahydrate. In aqueous solution, it provides both Na+ and Al3+ species and forms mildly acidic solutions typical of alum salts.

The solid is a hydrated double sulfate that crystallizes from solution as a highly hydrated salt. Its structure consists of aluminum centers coordinated by water molecules in octahedral geometry, linked by sulfate groups and balanced by sodium cations. The compound is well known for its high hydration state, containing twelve water molecules in its crystalline form, and it readily loses water upon heating.

Preparation typically involves crystallization from a mixture containing aluminum sulfate and sodium sulfate or from solutions of aluminum sulfate and sodium salts. The precise proportions and crystallization conditions determine the formation of the dodecahydrate. The material is highly soluble in water and gives solutions that are acidic due to hydrolysis of the aluminum center.

Uses of sodium aluminum sulfate dodecahydrate align with the broader alum family. It has historically been employed as a coagulant in water purification, helping to remove suspended particles. It is also used as a mordant in textile dyeing and printing, where it aids in fixing color to fibers. In some older formulations, alum salts served as leavening agents in baking powders, though these uses have declined due to concerns about aluminum intake.

Safety considerations are similar to other inorganic salts: handling should avoid inhalation and contact with eyes and skin, with standard laboratory or industrial hygiene practices.