Question

For the detection of phosphorus , the organic compound after fusion with $N{a}_2{O}_2$ is extracted with water, boiled with $HN{O}_3$ and then ammonium molybdate added to it. A yellow ppt. is obtained which is due to formation of :

• A. ammonium sulphate
• B. ammonium phosphomolybdate
• C. ferric phosphate
• D. disodium ammonium phosphate

Answer 1

The correct option is B ammonium phosphomolybdate

A very few organic compounds contain phosphorus. Its presence is detected by fusing the compound with an oxidizing mixture of sodium carbonate and potassium nitrate or with sodium peroxide alone when an alkali phosphate is formed. The fused mass is extracted with water and filtered. The filtrate containing sodium phosphate is heated with cone. $HN{O}_3$ and an excess of ammonium molybdate solution is added. A yellow ppt. or colouration if formed if phosphorus is present. The yellow precipitate is ammonium phosphomolybdate, ${\left(N{H}_4\right)}_3\left[P{Mo}_{12}{O}_{40}\right]$