Question

The phosphorus present in an organic compound of mass 10 g is oxidized to phosphoric acid by heating with fuming nitric acid. The phosphoric acid so obtained is precipitated as$MgN{H}_{4}P{O}_4$, which on ignition is converted into $M{g}_2{P}_2{O}_7$. If the mass of Mg2P2O7 is 5 g, the percentage composition of phosphorus present in the sample of the organic compound is:

• A. 13.96
• B. 14.96
• C. 15.96
• D. 12.96

Answer 1

The correct option is A 13.96

The mass of the organic compound is 10 g.

Mass of $M{g}_2{P}_2{O}_7$ formed = 5 g

Molar mass of $M{g}_2{P}_2{O}_7$ = 222 g

P is estimated as $M{g}_2{P}_2{O}_7$,

Then, percentage of phosphorous = (62 x 5 x 100%)/(222 x 10) =13.96%