Question

The chemical formula of brown ring formed in the brown ring test is .

• A. $\left(Fe\right(H_{2}O{)}_5\mathrm{NO}){\mathrm{SO}}_4$
• B. $\mathrm{Fe}(\mathrm{NO}{)}_2{\mathrm{SO}}_4$
• C. ${\mathrm{FeSO}}_4.{\mathrm{NO}}_3$

Answer 1

The correct option is A

To determine the presence of nitrate ions in any solution, a 'brown ring test' is conducted.

Step 1: The solution to be tested is taken in a test-tube
Step 2: Iron(II) sulphate is added to it
Step 3: Slowly concentrated sulphuric acid (H₂SO₄) is added such that the acid added forms a layer below the aqueous solution.
If a ring brown in colour is formed at the junction of the 2 layers, it indicates the presence of nitrate ion.
Its chemical formula is $\left[Fe\right(H_{2}O{)}_5\left(NO\right)]S{O}_4$

The equations for the same are given below.
$2HN{O}_3+3H_{2}S{O}_4+6FeS{O}_4⟶3F{e}_2(S{O}_4{)}_3+2NO+4H_{2}O$
$\left[Fe\right(H_{2}O{)}_6]S{O}_4+NO⟶[Fe\left(H_{2}O{)}_5\right(NO\left)\right]S{O}_4+H_{2}O$