Question

Why we are using freshly prepared ferrous sulphate solution in nitrate test?

Answer 1

$\huge \bold {ANSWER}$

$\underline \bold {TEST}$

BROWN RING TEST -For detection of nitrate radical $[{NO_3}^{-1}]$radical.

$\underline \bold {PROCEDURE}$

◼Take a solution of a nitrate or dilute nitric acid in a test tube.

◼Add to it a freshly prepared saturated solution of iron [II ] sulphate.

◼Add concentrate sulphuric acid carefully from the sides of the test tubes as the reaction is highly exothermic and the acid may spurt out.

◼Cool the test tube thoroughly from outside under a tap.

$\underline \bold {OBSERVATION }$

A brown ring appears at the junction of two liquids.

In the brown ring test the concentrate sulphuric acid being heavier settles down and iron [II] sulphate remains above it resulting in the formation of the brown ring at junction.

$\underline \bold {REASON }$

▶A freshly prepared iron [II ] sulphate solution is used in above test. Iron [II] sulphate on exposure to the atmosphere is oxidised to iron [III] sulphate and test will not answer with iron [III] sulphate.

$\underline \bold {EQUATION }$

$6FeSO_4 +3H_2SO_4 +2HNO_3 \longrightarrow 3Fe_2(SO_4)_3 + 4H_2O + 2NO$

$FeSO_4 + NO \longrightarrow FeSO_4NO$[Nitroso iron [II] sulphate ]