Question

Which of the following elements in an organic compound can be detected using ammonium molybdate?

• A. Carbon
• B. Phosphorus
• C. Nitrogen
• D. Sulphur

Answer 1

The correct option is B Phosphorus

Ammonium molybdate is used for detection of phosphorus in organic compound.
The compound is heated with an oxidising agent (sodium peroxide) so that the phosphorus present in the compound is oxidised to phosphate.
The solution is boiled with nitric acid and then treated with ammonium molybdate.
A yellow colouration or precipitate indicates the presence of phosphorus.
$N{a}_{3}P{O}_4+3HN{O}_3\stackrel{\Delta }{⟶}{H}_{3}P{O}_4+3NaN{O}_3$
$H_{3}P{O}_4+\underset{\text{Ammonium molybdate}}{12(N{H}_4{)}_{2}Mo{O}_4}+21HN{O}_3⟶\underset{\text{Ammonium phosphomolybdate}}{(N{H}_4{)}_{3}P{O}_4.12Mo{O}_3}\downarrow +21N{H}_{4}N{O}_3+12H_{2}O$