Identify Gas and Reagent from Brown Precipitate

 

❓ Question

When a salt is treated with NaOH, gas X is evolved.

Passing gas X through reagent Y gives a brown coloured precipitate.

Find X and Y.

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🖼 Question Image

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✍️ Short Concept

This is a salt analysis detection test.

👉 NaOH + ammonium salt → NH₃ gas

👉 NH₃ detected using Nessler’s reagent

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🔷 Step 1 — Gas Released with NaOH 💯

Ammonium salt + NaOH:

$$NH_4^+ + OH^- \rightarrow NH_3 + H_2O$$

So gas X is:

$$\boxed{NH_3}$$

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🔷 Step 2 — Detection of Ammonia

Ammonia is detected using:

$$\text{Nessler’s reagent}$$

Composition:

$$K_2HgI_4 + KOH$$

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🔷 Step 3 — Observation

NH₃ + Nessler’s reagent:

👉 Gives brown coloured precipitate

This confirms:

$$NH_3$$

presence.

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🔷 Step 4 — Identify Reagent Y

So reagent Y is:

$$\boxed{K_2HgI_4 + KOH}$$

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🔷 Step 5 — Final Matching

$$X = NH_3$$
$$Y = K_2HgI_4 + KOH$$

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✅ Final Answer

$$\boxed{X = NH_3,\quad Y = K_2HgI_4 + KOH}$$

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⭐ Golden JEE Insight

👉 NaOH + ammonium salt always releases NH₃

👉 Brown ppt with Nessler’s reagent = ammonia confirmation test.