• # question_answer In an organic compound, phosphorus is estimated as A) ${{H}_{3}}P{{O}_{4}}$              B) ${{P}_{2}}{{O}_{5}}$     C)      $M{{g}_{2}}{{P}_{2}}{{O}_{7}}$         D)      $M{{g}_{3}}{{(P{{O}_{4}})}_{2}}$

A pre-weighed amount of organic compound is heated with concentrated nitric acid $(HN{{O}_{3}})$in a tube. . Phosphorus present in the compound gets converted into phosphoric acid. Now the content of tube are heated with magnesia mixture, i.e., $MgS{{O}_{4}}+N{{H}_{4}}Cl+N{{H}_{4}}OH,$so that the magnesium ammonium phosphate $MgN{{H}_{4}}P{{O}_{4}}$is formed which is collected, washed, dried and ignited to get magnesium pyrophosphate$M{{g}_{2}}{{P}_{2}}{{O}_{7}},$which is then weighed. $\underset{\text{Phosphoric}\,\text{acid}}{\mathop{{{H}_{3}}P{{O}_{4}}}}\,\xrightarrow{\text{Magnesia}\,\text{mixture}}\,\underset{\begin{smallmatrix} \text{Magnesium}\,\text{ammonium} \\ \text{Phosphate}\,\text{(white}\,\text{ppt}\text{.)} \end{smallmatrix}}{\mathop{MgN{{H}_{4}}P{{O}_{4}}}}\,+3HCl$ $2MgN{{H}_{4}}P{{O}_{4}}\xrightarrow{\Delta }M{{g}_{2}}{{P}_{2}}{{O}_{7}}\downarrow +2N{{H}_{3}}+{{H}_{2}}O$ From here knowing the weight of $M{{g}_{2}}{{P}_{2}}{{O}_{7}},$the percentage of phosphorus can be found out. Hence, the correct option is (c).