It is also estimated by carius method the known mass of organic compound containing phosphorus is heated with fuming HNO3 when phosphorus is oxidised to phosphoric acid (H3PO4). To this, magnesia mixture (MgSO4 + NH4OH + NH3Cl) is added when phosphoric acid precipitates as magnesium ammonium phosphate (MgNH4PO4). This precipitate is filtered, washed, dried and ignited when it is converted to magnesium pyrophosphate (Mg2P2O3).
The weight of Mg2P2CO7 is determied from which the percentage of phosphorus is the compound can be calculated. Observations and Calculations:
1. Mass of organic compound taken = w1, g.
2. Mass of Mg2P2O7 obtained = W2g.
We have contains 62g of phosphorus.
W2g of Mg2P2O7 Will contain \(\frac{62\times w_2}{222}\)g of phosphorus
This amount of phosphorus was present in wig of the compound
∴ %P = \(\frac{62\times w_2}{222}\) x \(\frac{100}{w_1}\)