Question

In qualitative test for identification of presence of phosphorous, the compound is heated with an oxidising agent. Which is further treated with nitric acid and ammonium molybdate respectively. The yellow coloured precipitate obtained is :

(1) \(Na_3 PO _4.12 MoO_3\)

(2) \((NH_4)_3 PO_4 .12 (NH_4)_2 MoO_4\)

(3) \((NH_4) _3 PO_4 .12 MoO_3\)

(4) \(MoPO_4 .21 NH_4 NO_3\)

Answer 1

 Correct option is (3) \((NH_4) _3 PO_4 .12 MoO_3\)

\(2P+3Na_2 O_2 + \underset {air}{O_2} \xrightarrow{fusion} 2Na_3 PO_4\)

\(Na_3 PO_4 + 12(NH_4)_3 MoO_4 + 21 HNO_3 \rightarrow \) \((NH_4)_3 PO_4. \underset{yellow}{12MoO_3}+21 NH_4 NO_3 + 12 H_2O\)

The organic compound is fused with sodium peroxide. The fused mass is then extracted with water. The aqueous solution so obtained is boild with concentrated nitric acid, and ammonium molybdate solution is added to it. A yellow solution or precipitate indicates the presence of phosphorus in the organic compound. The yellow precipitate is of ammonium phosphomolybdate.