Test for Phosphate Ion using Nitric Acid and Ammonium Molybdate

I haven't learned anything about pH levels yet, but I'm assuming this means the phosphate ions are binding with the hydrogen from the nitric acid, producing the phosphoric acid used in the equation.

If my assumption is correct, thank you so much because this definitely solves my problem :-)

Nitric acid doesn't take part in the reaction as a whole, from what I remember it is there to keep the pH low and to keep redox potential in the solution high to not allow side reactions.

Try

H₃PO₄ + (NH₄)₂MoO₄ + H⁺ -> (NH₄)₃PO₄·12MoO₃·2H₂O + NH₄⁺ + H₂O

(this is one of many ways of expressing the phosphomolybdate formula).

Quote from:

I'm uncertain about the phosphoric acid instead of the phosphate ions being part of the reactants.

What fraction of phosphates is completely protonated in the low pH produced by adding excess nitric acid?

Thank you, Borek - leaving out the nitric acid does make sense since I've read the precipitate is insoluble in nitric acid so it should be viewed suspended there.

However, I'm uncertain about the phosphoric acid instead of the phosphate ions being part of the reactants. Is that what would be present in a sample of blood?

Thank you again for your *delete me* I really want to get this assignment right.