Give the test for detection of P in an organic compound.

Explanation

Estimation of phosphorus
The given organic compound is heated with fuming nitric acid. It oxidises the phosphorus into phosphoric acid. Now, the phosphoric acid is precipitated as `MgNH_4PO_4` by adding magnesia mixture `(NH_4Cl + MgCl_2 "and a little" NH_OH)`. Further, on ignition, `MgNH_4PO_4` yields `Mg_2P_2O_7` from which phosphorus can be estimated.
`underset("(From organic compound)")(2P) + underset(("From"H_2O))(5O) overset("Heat")(rarr)P_2O_3`
`P_2O_5 + 3H_2O overset("Heat")(rarr) 2H_3PO_4`
`H_3PO_4 + underset("(Magneisa mixture)")((NH_4Cl + MgCl_2)) to MgNH_4PO_4`
`2MgNH_4PO_4 overset("Heat")(rarr)underset("Magnesium Pyrophosphate")(Mg_2P_2P_7) + 2NH_3 + H_2O`
Calculations :
Let the mass of organic compound = mg
Mass of magnesium pyrophosphate = ag
`Mg_2P_2O_7 = 2P `
`2 xx 24 + 2 xx 31 + 7 xx 16 = 2 xx 31 `
`222 = 62 `
222 g of `Mg_2P_2O_7` contain phosphorus = 62 g ,
ag of `Mg_2P_2Q_7` contain phosphorus= ` 62/222 xx ag`
Hence , % age of phosphorus = `("Mass of phosphorus")/("Mass of organic compound") xx 100`
`= (62a)/222 xx 100/m %`