Question

Analytical Chemistry Problem

0.352g of organic phosphate sample is digested and dissolved in hydrochloric acid followed by the addition of Mg²⁺ solution in ammoniacal medium. The precipitate, MgNH₄PO₄, 6H₂0 is filtered, washed free from impurities and then ignited at 1000^oC to constant weight to convert the precipitate to Mg₂P₂O₇ which is found to weigh 0.6144g. Calculate the %P in the sample.

Answer 1

Mass of Mg₂P₂O₇ precipitate=0.6144g

Mass of Mg₂P₂O₇ precipitate=0.6144/222=2.7676*10^-3 mol

Moles of P in compound=2*moles of Mg₂P₂O₇=2*2.7676*10^-3

                                                =5.535*10^-3 mol

Mass of P in sample=5.535*10^-3*31=0.1716 g

%P in sample=(0.1716/0.352)*100=48.75%