Presence of Phosphate reaction equation

[Redrang604]

What are the balanced redox equations that take place between Ammonium Molybdate [(NH4)6Mo7O24:4H20], Stannous Chloride [snCl2:2H20], and Phosphate that form Molybdenum Blue [Mo5O14]?

[woelen]

Before asking that question, first try to determine, what are the other products of this reaction.

 

To my opinion, the answer to your question will be almost impossible. The chemistry of molybdenum is remarkably complex and I doubt whether the molybdenum blue, as you call it, is a single well-defined compound with a certain stoichiometry. The only thing, which really can be said about it, is that it contains Mo in mixed oxidation states and that it the cause of the intense color of this material (compare with prussian blue and mixed oxidation state copper(I)/copper(II)/chloride complexes).

 

Anyways, the tin is oxidized to tin (IV) and probably will form hydrous SnO2 under the conditions of the reaction.

 

The role of the phosphate is to form very complicated polymetallate ions, containing both phosphorous and molybdenum. Without the tin (II), a yellow compound is formed of unbelievable complex structure (which still is not yet fully determined), which contains large anionic species, which consist of phosphorus, molybdenum and oxygen. With the ammonium ions this gives a precipitate.

These mixed anionic species are more sensitive to reduction than molubdenum (VI) species alone. The phosphomolybdate structure has another color, but it also enhances reactivity of molybdate (VI). Why? I don't know, and rpobably noone knows precisely. On the other hand, the formation of that yellow compound is a very sensitive test for presence of phosphate, and combined with the reduction to blue compounds, it can be made even more sensitive (but also less selective).