Question

In the brown ring test, the brown colour of the ring is due to _______

1. ferrous nitrate

2. ferrous nitrososulphate

Answer 1

2. Ferrous nitrososulphate

When a freshly prepared acidified solution of ferrous sulphate is added to a solution of nitrate ions, in the presence of conc. $H_{2}S{O}_4$, a deep brown ring is formed. This deep brown ring is due to the formation of the complex sphere $\left[\right(Fe\left(H_{2}O{)}_{5}NO\right]S{O}_4$. i.e. Ferrous nitrososulphate.