Question: Concentrate nitric acid oxidises phosphorus to phosphoric acid according to the following equation: ...

Question

Concentrate nitric acid oxidises phosphorus to phosphoric acid according to the following equation:
$P + 5HN{O_3}(conc.) \to {H_3}P{O_4} + {H_2}O + 5N{O_2}$
If $9.3g$ of phosphorus was used in the reaction, calculate:
The mass of phosphoric acid formed.

Answer 1

Solution

To find the mass of phosphoric acid formed, we have to first find the molecular weight of the substance which is phosphoric acid. The mass of a substance's molecule is calculated in molecular weight, which is dependent on $12$ as the atomic weight of carbon is $12$ .

Complete answer:
$P + 5HN{O_3}(conc.) \to {H_3}P{O_4} + {H_2}O + 5N{O_2}$
We have to first find out the molecular weight of phosphoric acid .
Phosphoric acid is a weak acid with the chemical formula ${H_3}P{O_4}$ . It is also called orthophosphoric acid or phosphoric acid. It's usually found in the form of a colourless syrup with an eighty five percent concentration of water.
Molecular weight of phosphoric acid $[{H_3}P{O_4}]$
$= 1 \times 3 + 31 + 16 \times 4 \\\ = 98 \\\$
We got $1 \times 3$ as the molecular weight of hydrogen is one and there are three hydrogen atoms.
We got $31 \times 1$ as the molecular weight of phosphorus is thirty-one and there is only one phosphorus atom.
We got $16 \times 4$ as the molecular weight of oxygen is sixteen and there are four oxygen atoms.
If $31g$ of phosphorus produces $98g$ of phosphoric acid,
Then $1g$ of phosphorus produces $\dfrac{{98}}{{31}}g$ of phosphoric acid,
Hence $9.3g$ of phosphorus produces $\dfrac{{98}}{{31}} \times 9.3g$ of phosphoric acid.
$\Rightarrow \dfrac{{98}}{{31}} \times 9.3g = 29.39g = 29.4g$
Therefore, if $9.3g$ of phosphorus was used in the reaction, then the mass of phosphoric acid formed $= 29.4g$

Note:
Phosphoric acid is used in fertilisers (which account for eighty percent of overall use), detergents, and a variety of cleaning items. Since the dilute solutions may have a pleasant acid flavour, it is also used as a food additive to give soft drinks and other processed foods acidic properties, as well as in water treatment devices.