Na2MoO4

Sodium molybdate, with the chemical formula Na2MoO4, is the sodium salt of molybdic acid. It is commonly encountered as the dihydrate Na2MoO4·2H2O, though the anhydrous salt exists and is hygroscopic. It can be prepared by neutralizing molybdic acid (H2MoO4) with sodium hydroxide or by reacting MoO3 with NaOH to form Na2MoO4, which crystallizes from aqueous solution as the dihydrate.

Na2MoO4 is a white, odorless solid that dissolves readily in water. In solution it forms the molybdate anion (MoO4^2−). Aqueous solutions are mildly basic, with the exact pH depending on concentration. On heating, the dihydrate loses water to yield the anhydrous salt. In strongly acidic solutions, MoO4^2− is protonated to form species such as HMoO4^− and H2MoO4, reflecting usual molybdate equilibria.

Applications of sodium molybdate include its use as a source of molybdate ions in agriculture and horticulture, where it serves as a micronutrient to address molybdenum deficiencies in soils and hydroponic systems. In industrial water treatment, it acts as a corrosion inhibitor, helping protect metal surfaces in boiler and cooling systems. It also serves as a reagent and precursor in chemical synthesis and catalysis, providing Mo-containing species for various reactions and for the preparation of catalysts and other molybdenum compounds.

Safety considerations include handling to avoid inhalation of dust and contact with skin or eyes. Sodium molybdate is of relatively low acute toxicity but should be stored and used with appropriate personal protective equipment, and spills should be contained to prevent environmental release.