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 :

• A. Na$_3$PO$_4$.12MoO$_3$
• B. (NH$_4$)$_3$PO$_4$.12(NH$_4$)$_2$MoO$_4$
• C. (NH$_4$)$_3$PO$_4$.12MoO$_3$
• D. MoPO$_4$.21NH$_4$NO$_3$

Answer 1

Answer: (C)

(NH$_4$)$_3$PO$_4$.12MoO$_3$

Answer 2

In the qualitative analysis of phosphorus, the following reaction occurs:
$\text{PO}_4^{3-} \text{ or } \text{HPO}_4^{2-} + (\text{NH}_4)_2\text{MoO}_4 \xrightarrow{\text{H}^+} (\text{NH}_4)_3\text{PO}_4 \cdot 12\text{MoO}_3 \downarrow$
The product, $(\text{NH}_4)_3\text{PO}_4 \cdot 12\text{MoO}_3$, is a canary yellow precipitate known as ammonium phosphomolybdate.