The analytical method is based on the following
reactions [3]:
H3PO4 q- 12 H2Mo1204 ----+ H3P(Mo12040) + 12 H20
Mo(VI) reducing agent Mo (V)
slow
There is however reason to doubt the stoichiometry of
the reactions because of the different heteropolyanions
that can be formed between Mo and PO43 -. The
reductions are most commonly of 2 electron equivalents
but may be up to 6 electron equivalents. The
reduction evidently occurs on individual Mo atoms,
producing a proportion of Mo v ions. Transfer from
Mo V to Mo vI is then responsible for the intense
'charge transfer' absorption.