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

Hint: 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.