Na2HPO42H2O

Na2HPO4·2H2O, commonly written as Na2HPO4·2H2O and known as disodium hydrogen phosphate dihydrate, is the dihydrate salt of disodium hydrogen phosphate derived from phosphoric acid. It consists of two sodium ions, one hydrogen phosphate anion, and two water molecules of crystallization. The compound has a high molar mass of about 178.0 g/mol and forms white, crystalline solids that are highly soluble in water, yielding a basic solution.

Physically, the dihydrate form tends to crystallize from aqueous solutions and remains stable at room temperature. In aqueous solution, Na2HPO4·2H2O acts as a base due to the hydrolysis of the hydrogen phosphate ion, contributing to buffering capacity in systems where a pH around the alkaline range is required. It is often used with the corresponding acid salt NaH2PO4 to create phosphate buffer systems with adjustable pH.

Preparation and occurrence: Na2HPO4·2H2O is produced industrially by the neutralization of phosphoric acid with sodium compounds (such as sodium hydroxide or sodium carbonate) to form Na2HPO4, followed by crystallization as the dihydrate. It is a common laboratory and industrial reagent and may be isolated as the dihydrate by controlled evaporation and drying conditions.

Applications: The compound serves as a buffering agent in biochemical and clinical buffers, foods, and pharmaceuticals, helping to regulate acidity. It is also used in some water treatment and cleaning formulations and as a source of phosphate in various analytical and industrial processes.

Safety and handling: Na2HPO4·2H2O is of low acute toxicity but can act as an irritant to eyes and skin. It should be handled with standard laboratory hygiene, stored in a cool, dry place, and kept away from incompatible materials.