Sodium Tetramolybdate, Na₂O.4MoO₃

Sodium Tetramolybdate, Na₂O.4MoO₃, can be obtained from the mother-liquor from the crystallisation of the trimolybdate. Hydrates with 5.5 and 6H₂O, as well as the anhydrous salt, have been described, but the constitution of the salt usually obtained has been stated to be Na₆H₄[H₂(Mo₂O₇)₆]21H₂O. The salt yields yellow microscopic crystals. The acid salt NaHMo₄O₁₃.8H₂O has been prepared by interaction of four molecular proportions of "normal" sodium molybdate with seven of hydrochloric acid. Two octamolybdates, Na₂Mo₈O₂₅.4H₂O, or Na₂Mo₈O₂₅.17H₂O, and NaHMo₈O₂₅.4H₂O, which may also be considered as hydrogen tetramolybdates, have been prepared.

A pentamolybdate, NaHMo₅O₁₆.10H₂O, and decamolybdates, of composition Na₂MO₁₀O₃₁.12H₂O, or possibly Na₂MO₁₀O₃₁.6H₂O, and Na₂MO₁₀O₃₁.22H₂O, have been described.

The double salt 2Na₂MoO₄.K₂MoO₄.14H₂O is known, as also are the salts LiNa₃(MoO₄)₂.6H₂O and K₂Na₄(MoO₄)₃.14H₂O.