Class 12 Chemistry Practical
How to do salt analysis · Viva · Quiz
To analyse the given inorganic salt for one acidic and one basic radical.
| Experiment | Observation | Inference |
|---|---|---|
| Physical examination | White crystalline solid; ammoniacal smell | May be an ammonium salt |
| Solubility | Readily soluble in water | Water-soluble salt |
| Dry heating | Salt sublimes; white sublimate on the cooler parts; smell of ammonia | NH₄Cl (sal ammoniac) indicated |
| Flame test | No characteristic flame colour | Not Na⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺ |
| Dilute H₂SO₄ | No characteristic gas | CO₃²⁻, S²⁻, SO₃²⁻, NO₂⁻, CH₃COO⁻ absent |
| Conc. H₂SO₄ | Colourless pungent gas; white fumes with NH₄OH | Cl⁻ may be present |
| Experiment | Observation | Inference |
|---|---|---|
| Heat a pinch of salt with conc. H₂SO₄ | Colourless gas with a pungent smell; dense white fumes with NH₄OH | Cl⁻ may be present |
| Confirmatory Tests | ||
| MnO₂ / conc. H₂SO₄ Heat the salt with conc. H₂SO₄ and a pinch of MnO₂ | Greenish-yellow chlorine gas is evolved | Cl⁻ is indicated |
| Silver nitrate Acidify the soda extract with dilute HNO₃ and add AgNO₃, then NH₄OH | Curdy white ppt of AgCl, soluble in NH₄OH, reappears with dilute HNO₃ | Cl⁻ is confirmed |
| Chromyl chloride Heat salt + K₂Cr₂O₇ + conc. H₂SO₄. Pass vapours into NaOH; acidify with acetic acid and add lead acetate | Yellow chromyl chloride vapours; yellow ppt of PbCrO₄ | Cl⁻ is confirmed (chromyl chloride test) |
| Experiment | Observation | Inference |
|---|---|---|
| Heat the salt with NaOH solution | Ammoniacal smell; gas turns red litmus blue | NH₄⁺ may be present (Group 0) |
| Bring a glass rod dipped in conc. HCl near the mouth of the tube | Dense white fumes of NH₄Cl | NH₄⁺ may be present |
| Confirmatory Test | ||
| Nessler’s reagent Pass the gas into Nessler’s reagent (K₂[HgI₄] in KOH) | Brown colouration or brown ppt of basic mercury(II) amidoiodide | NH₄⁺ is confirmed. Stop cation analysis here for ammonium salts. |
The given salt contains NH₄⁺ as the cation (basic radical) and Cl⁻ as the anion (acidic radical). The salt is Ammonium Chloride (NH₄Cl).
Why does NH₄Cl sublime on dry heating?
It dissociates to NH₃ and HCl which recombine on the cooler parts of the tube as a white sublimate.
Why is Nessler’s reagent used?
It gives a characteristic brown ppt with ammonia, confirming NH₄⁺ even in small amounts.
Why is AgNO₃ added after acidifying with HNO₃?
HNO₃ prevents phosphates, oxalates and carbonates of silver from precipitating; only AgCl / AgBr / AgI ppt.
Why white fumes with a HCl-dipped rod?
NH₃ + HCl → NH₄Cl smoke.
Why is the chromyl chloride test not given by bromides/iodides?
They form Br₂ / I₂, not a chromyl compound analogous to CrO₂Cl₂.
Why must the original solution not be made in conc. HCl for NH₄Cl?
The salt is already a chloride; water extract is enough. Group I HCl is for other cations.
Why does red litmus turn blue with the gas?
Ammonia is alkaline.
How is NH₄Cl used in Group III?
NH₄Cl suppresses [OH⁻] by common-ion effect so only Group III hydroxides ppt, not Mg(OH)₂.
नमक: अमोनियम क्लोराइड। अम्लीय मूलक: क्लोराइड (Cl⁻)। क्षारीय मूलक: अमोनियम (NH₄⁺)।
गंध अमोनिया जैसी होती है, गंधहीन नहीं। शुष्क ऊष्मा पर नमक उर्ध्वपातित हो जाता है।
क्लोराइड की पुष्टि AgNO₃ से सफेद अवक्षेप (NH₄OH में घुलनशील) से होती है। अमोनियम की पुष्टि नैस्लर अभिकर्मक से भूरे अवक्षेप से होती है।