Molybdates

salts of molybdic acids. Two types of molybdates are known: normal molybdates (salts of molybdic acid, H₂MoO₄) and polymolybdates (salts of isopolymolybdic acids). All normal molybdates, except the molybdates of alkali metals and magnesium, are poorly soluble in water. The most important soluble molybdate is Na₂MoO₄, which is used in the manufacture of dyes and varnishes; soluble molybdates are widely used as trace fertilizers.

Naturally occurring calcium, iron, and lead salts are among the most valuable poorly soluble molybdates. Calcium molybdates are also used to introduce molybdenum in the manufacture of alloy steels. Examples of isopolymolybdates include sodium di-, tri-, and tetra-molybdates, Na₂Mo₂O₇, Na₂Mo₃O₁₀, and Na₂Mo₄O₁₃, respectively. Polymolybdates such as sodium paramolybdate, Na₆Mo₇O₂₄ · xH₂O, and ammonium paramolybdate, (NH₄)₆Mo₇O₂₄ · xH₂O, have acquired wide practical significance. The latter is usually the final product in the processing of molybdenum concentrates and is widely used as a reagent.