Chemistry - Stoichiometry Question with Solution | TestHub

In a gravimetric determination of P of a aqueous solution of dihydrogen phosphate in ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}$is treated with a mixture of ammonium and magnesium ions to precipitate magnesium ammonium phosphate, $\mathrm{Mg}\left({\mathrm{NH}}_4\right){\mathrm{PO}}_4\cdot 6{\mathrm{H}}_2\mathrm{O}$. This is heated and decomposed to magnesium pyrophosphate, ${\mathrm{Mg}}_2{\mathrm{P}}_2{\mathrm{O}}_7$. A solution of ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}$yielded 4.621 g of ( ${\mathrm{Mg}}_2{\mathrm{P}}_2{\mathrm{O}}_7$ ) which is weighed. What weight of ${\mathrm{NaH}}_2{\mathrm{PO}}_4$ was present originally ? $(\mathrm{Mg}=24,\mathrm{P}=31,\mathrm{Na}=23)$