Question

When a substance reacts with dil. sulphuric acid a light brown gas is evolved when a filter paper moistened with acidified starch iodide solution is brought on the month of the test, it is turned blue. The acidic radical in the salt is :

• A. Sulphide
• B. Nitrate
• C. Carbonate
• D. Nitrite

Answer 1

Answer: (D)

On treating solid nitrite with dil. $H_{2}S{O}_4$, nitric oxide ($NO$) gas is evolved which readly gives brown fumes of $N{O}_2$ with the oxygen of the air.

Nitrites react with potassium iodide in the presence of dilute sulphuric acid to liberate iodine. Iodine forms a blue-black complex with starch.

$2KI+2H_{2}S{O}_4+2HN{O}_2⟶2KHS{O}_4+I_2+2NO+2H_{2}O$

$I_2+Starch⟶Blue-BlackComplex$