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 solid; ammoniacal smell | Ammonium salt |
| Solubility | Soluble in water | Unlike CaCO₃ / BaCO₃, ammonium carbonate dissolves |
| Dry heating | NH₃ and CO₂ evolved; salt may disappear (volatile) | Ammonium carbonate |
| Dilute H₂SO₄ | Brisk effervescence of CO₂; lime water milky | CO₃²⁻ present |
| Conc. H₂SO₄ | CO₂ evolved; no halide fumes | Carbonate, not halide |
| Flame test | No characteristic colour | Not Ba / Sr / Ca |
| Experiment | Observation | Inference |
|---|---|---|
| Add dilute H₂SO₄ (or dilute HCl) to the salt | Brisk effervescence; colourless, odourless gas | CO₃²⁻ may be present |
| Confirmatory Test | ||
| Lime water Pass the gas through lime water. Continue passing in excess | Lime water turns milky; milkiness disappears on excess CO₂ | CO₃²⁻ is confirmed |
| 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 CO₃²⁻ as the anion (acidic radical). The salt is Ammonium Carbonate ((NH₄)₂CO₃).
Why brisk effervescence with dilute acid?
Carbonate + acid → CO₂.
How do you distinguish CO₂ from SO₂?
SO₂ has a burning-sulphur smell and decolourises acidified KMnO₄ / K₂Cr₂O₇; CO₂ does not.
Why is this salt soluble unlike chalk?
Alkali and ammonium carbonates are soluble; Group II carbonates are not.
Why Nessler after NaOH?
NaOH liberates NH₃; Nessler confirms it.
Why Group 0 first?
NH₄⁺ would interfere later (NH₄OH is a group reagent). Always test ammonium first.
What happens on strong heating?
Ammonium carbonate decomposes completely to gases.
Why milkiness of lime water?
Insoluble CaCO₃.
Can sulphite give lime water milky?
SO₂ also turns lime water milky (CaSO₃). Smell and KMnO₄ distinguish it.
नमक: अमोनियम कार्बोनेट। तनु अम्ल से तेज़ बुदबुदाहट (CO₂), चूने का पानी दूधिया।
क्षारीय मूलक अमोनियम है। NaOH और नैस्लर। वर्ग I-VI आगे नहीं चलाते।
यह नमक जल में घुलनशील है, कैल्शियम कार्बोनेट (चाक) नहीं।