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Q.
In an organic compound, phosphorus is estimated as
AFMCAFMC 2010Organic Chemistry – Some Basic Principles and Techniques
Solution:
In Carius method, the weighed organic compound (containing phosphorus) is heated with conc $HNO _{3}$ followed by $MgCl _{2}$ in the presence of $NH _{4} Cl$ and $NH _{4} OH$. By this magnesium ammonium phosphate, $MgNH _{4} PO _{4}$ is formed which on ignition gives magnesium pyrophosphate $\left( Mg _{2} P _{2} O _{7}\right)$. From the amount of magnesium pyrophosphate, the percentage of phosphorus is calculated as
$\%$ of $P =\frac{62}{222} \times \frac{\text { wt. of } Mg _{2} P _{2} O _{7}}{\text { wt. of substance taken }} \times 100$