Question

Why is a fresh solution of ${\mathrm{FeSO}}_4$ used in the test for nitrogen?

Answer 1

Nitrogen:

• The atomic number of nitrogen is seven, and the symbol for it is N. Nitrogen is a nonmetal and the lightest member of the periodic table's group fifteen, often known as the pnictogens.
• It's a plentiful element across the universe, with the Milky Way and Solar System having the sixth-highest total abundance.

${\mathrm{FeSO}}_4$ the fresh solution:

• After being reduced, ferrous sulphate reacts with nitrogen to produce colourful ions. This test is often used to assess the presence of nitrogen.
• It quickly oxidises to ferric sulphate and has no effect on brown ring formation. As we all know, the brown ring is a common nitrate test that is used to detect nitrate ions because a brown ring forms at the junction of the two layers, i.e. the acid and the sulphate solution, indicating the presence of nitrate ions. As we all know, the brown ring is a common nitrate test that is used to detect nitrate ions because a brown ring forms at the junction of the two layers, i.e. the acid and the sulphate solution, indicating the presence of nitrate ions.
• The ring test for nitrate ions is performed when freshly prepared ferrous sulphate is added to an aqueous solution of nitrate and sulphuric acid.$$\begin{gathered} 2{\mathrm{HNO}}_3\left(\mathrm{aq}\right)+3{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+6{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)\to 3{\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)+2\mathrm{NO}\left(\mathrm{aq}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right) \\ \left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]{\mathrm{SO}}_4\left(\mathrm{aq}\right)+\mathrm{NO}\left(\mathrm{aq}\right)\to \left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{NO}\right]{\mathrm{SO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right) \end{gathered}$$