in a gravimetric determination 4 of P , an aqueous solution of dihydrogen phosphate ion ( H2PO4 - ) is treated with a mixture of ammonium and magnesium ions to precipitate magnesium ammonium phosphate [ Mg( NH4)PO4,6H20 ]. This is heated and decomposed to magnesium pyrophosphate (Mg2P2O7), which is weighed . A solution of H2PO4- yielded 1.054 g of Mg2P2O7 . What weight of NaH2PO4 was present originally