VCAA 2011 Q4a) need help

[charmanderp]

If you read the question it says that all the phosphorous present is in the form of P2O5 and MgNH4PO4.6H2O. Since we don't actually lose or gain any phosphorous the amount of phosphorous in each is the same - essentially P2 is equivalent to MgNH4PO4.6H2O which is equivalent to PO4 which is equivalent to P. In P2O5 the amount of P2O5 is half the amount of P2, so the amount of P2O5 is half the amount of MgNH4PO4.6H2O.

[Tonychet2]

yea sorry i meant the mole ratio of n(p2o5) is 1:2 not the mols of n(p2o5) is double the mol of n(MgNH4PO4.6H2O) oops lol my wording was terrible