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  4. Heating 0.75 g of an organic compound containing phosphorus, with conc. HNO3 in the Carius tube followed by reaction with magnesia mixture gives MgNH4PO4. This on ignition left a residue of Mg2P2O7 weighing 1.2545 g. Calculate the percentage of phosphorus in organic compound.

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Q. Heating 0.75 g of an organic compound containing phosphorus, with conc. $HNO_3$ in the Carius tube followed by reaction with magnesia mixture gives $MgNH_4PO_4$. This on ignition left a residue of $Mg_2P_2O_7$ weighing 1.2545 g. Calculate the percentage of phosphorus in organic compound.

Organic Chemistry – Some Basic Principles and Techniques

Solution:

Mass of the organic compound $= 0.75\, g$
Mass of $Mg_2P_2O_7 = 1.2545\, g$
Thus, percentage of P
$=\left(\frac{62}{222}\right)\times\frac{mass \,of \,Mg_{2}P_{2}O_{7}}{mass \,of \,org.\, compound} \times 100$
$= \frac{62}{222} \times \frac{1.2545}{0.75}\times100 = 46.7\% \approx 47\%$