Question

Concentrated nitric acid oxidizes phosphorus to phosphoric acid according to the following equation:

$\mathrm{P}+5{\mathrm{HNO}}_3\to {\mathrm{H}}_3{\mathrm{PO}}_4+{\mathrm{H}}_2\mathrm{O}+5{\mathrm{NO}}_2$

(a) What mass of phosphoric acid can be prepared from $6.2\mathrm{g}$ of phosphorus?

Answer 1

Given information

• Phosphorus $\left(\mathrm{P}\right)$ reacts with nitric acid $\left({\mathrm{HNO}}_3\right)$ and results in the formation of phosphoric acid $\left({\mathrm{H}}_3{\mathrm{PO}}_4\right)$, water $\left({\mathrm{H}}_2\mathrm{O}\right)$ and nitrogen dioxide $\left({\mathrm{NO}}_2\right)$.
• The given reaction is as follows:

$\mathrm{P}+5{\mathrm{HNO}}_3\to {\mathrm{H}}_3{\mathrm{PO}}_4+{\mathrm{H}}_2\mathrm{O}+5{\mathrm{NO}}_2$

• The given mass of Phosphorus$=6.2\mathrm{g}$.

Calculation of molecular weight of phosphoric acid

Molecular weight of ${\mathrm{H}}_3{\mathrm{PO}}_4$$\begin{array}{rcl}& =& \left(1\mathrm{g}\times 3+31\mathrm{g}+16\mathrm{g}\times 4\right)=98\mathrm{g}\end{array}$

Calculation of mass of phosphoric acid

• $31\mathrm{g}$ of phosphorous can be prepared from $98\mathrm{g}$ of phosphoric acid.
• Thus, $6.2\mathrm{g}$ of phosphorous can be prepared from $\frac{98\mathrm{g}}{31\mathrm{g}}\times 6.2\mathrm{g}=19.6\mathrm{g}$ of phosphoric acid.

Therefore, $19.6\mathrm{g}$ of phosphoric acid can be prepared from $6.2\mathrm{g}$ of phosphorus.