Ammonia Detection Using Nessler Reagent Trick

 

❓ Concept Question

How do we identify NH₃ gas in salt analysis using confirmatory tests?

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🖼 Concept Image

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✍️ Short Concept

This is a standard ammonium salt detection test.

👉 NaOH releases NH₃ gas
👉 Nessler’s reagent confirms NH₃ by brown ppt.

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🔷 Step 1 — NaOH + Ammonium Salt 💯

If a salt gives gas with NaOH:

$$NH_4^+ + OH^- \rightarrow NH_3(g) + H_2O$$

So gas X is:

$$\boxed{NH_3}$$

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🔷 Step 2 — Brown Precipitate Clue

Brown coloured precipitate:

👉 Direct indication of Nessler’s test.

Reagent Y:

$$K_2HgI_4 + KOH$$

This is called:

$$\textbf{Nessler’s Reagent}$$

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🔷 Step 3 — Confirmation Reaction

When NH₃ passes through Nessler’s reagent:

👉 Brown precipitate forms

This confirms:

$$NH_3$$

presence.

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🔷 Step 4 — Concept Lock

Always remember flow:

$$NaOH \rightarrow NH_3$$
$$NH_3 + \text{Nessler’s reagent} \rightarrow \text{Brown ppt}$$

👉 This is a standard salt analysis sequence.

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🔷 Step 5 — JEE Trap Alert 🚨

❌ HgO dekh ke confuse ho jaana

❌ Brown ppt ko Fe(OH)₃ samajh lena

❌ Gas ko HCl assume kar lena

👉 Brown ppt + NH₃ = Nessler’s confirmation test.

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✅ Final Takeaway

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

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⭐ Golden JEE Insight

Salt analysis questions are mostly:

👉 Observation-based memory questions

So:

Colour + reagent = instant answer.