Discuss the principle of estimation of halogens, sulphur and phosphorus present in an organic compound.
Estimation of halogens: It involves oxidising the organic substance with fuming nitric acid in the presence of silver nitrate. The halogen of the substance is thus converted to silver halide which is separated and weighed.
Weight of organic compound= W gm
Weight of silver halide=x gm
Estimation of sulphur: the organic substance is heated with fuming nitric acid but no silver nitrate is added. The sulphur of the substance is oxidised to sulphuric acid which is then precipitated as barium sulphate by adding excess of barium chloride solution. From the weight of BaSO4 so obtained the percentage of sulphur can be calculated.
% Sulphur = 
⇒ % Sulphur = 
Estimation of phosphorous: The organic substance is heated with fuming nitric acid whereupon phosphorous is oxidised to phosphoric acid. The phosphoric acid is precipitated as ammonium phosphomolybdate. (NH4)3PO4.12MoO3 by the addition of ammonia and ammonium molybdate solution which is then separated, dried and weighed.
Where Molar mass of (NH4)3PO4.12MoO3 =1877g
If phosphorus is estimated as Mg2P2O7
% of P=