Question

A Colorless solid A liberates a brown gas B on acidification, a colorless alkaline gas (C) on treatment with NaOH and a colorless non-reactive gas D on heating. If heating of the solid is continued, it completely disappears.

Answer 1

A = ammonium nitrite (NH₄NO₂)

Gas B = NO₂

Gas C = NH₃

Gas D = N₂

Answer 2

Explanation

Let A be NH₄NO₂ (ammonium nitrite). When acidified:

NH₄NO₂ + H⁺ → NH₄⁺ + HNO₂

HNO₂ then decomposes: 2 HNO₂ → NO + NO₂ + H₂O

The brown gas observed is NO₂.

On treatment with NaOH, the ammonium ion reacts:

NH₄⁺ + OH⁻ → NH₃ (gas) + H₂O

Here, NH₃ is colorless and alkaline.

Upon heating, ammonium nitrite decomposes completely:

NH₄NO₂ → N₂ (gas) + 2 H₂O

The gas N₂ (non‐reactive and colorless) is liberated, and the solid disappears.