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 | Ammonium oxalate is soluble |
| Dry heating | NH₃ evolved; residue may char slightly; CO / CO₂ on stronger heating with acid later | Ammonium + oxalate |
| Dilute H₂SO₄ | No brisk CO₂ like carbonate | Not carbonate |
| Conc. H₂SO₄ | CO + CO₂; CO burns with a blue flame | Oxalate indicated |
| Flame test | No characteristic colour | Not Ba / Ca / Sr |
| Experiment | Observation | Inference |
|---|---|---|
| Heat the salt with conc. H₂SO₄ | Colourless gases (CO + CO₂); CO burns with a blue flame at the mouth | C₂O₄²⁻ may be present |
| Confirmatory Tests | ||
| Calcium chloride Acidify the extract with acetic acid and add CaCl₂ | White ppt of calcium oxalate, insoluble in acetic acid, soluble in HCl | C₂O₄²⁻ is confirmed |
| KMnO₄ To the oxalate ppt add dilute H₂SO₄ and warm with dilute KMnO₄ | Pink colour of KMnO₄ is discharged | C₂O₄²⁻ 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 C₂O₄²⁻ as the anion (acidic radical). The salt is Ammonium Oxalate ((NH₄)₂C₂O₄).
Why blue flame at the mouth with conc. H₂SO₄?
CO burns with a blue flame; CO₂ does not burn.
Why CaCl₂ in acetic acid?
Calcium oxalate is insoluble in acetic acid; calcium phosphate / carbonate would not survive acetic acid the same way.
Why warm KMnO₄?
The redox reaction is slow in the cold; it is autocatalysed by Mn²⁺ on warming.
Why Nessler?
Ammonium cation.
Why not lime water as the main anion test?
CO₂ from oxalate + conc. H₂SO₄ is mixed with CO; dilute acid does not give brisk carbonate-like CO₂.
Why Group 0 first?
Always, for any ammonium salt.
Difference from ammonium carbonate?
Carbonate: dilute acid, lime water. Oxalate: conc. H₂SO₄, CaCl₂, KMnO₄.
Why is the salt used as a Group V reagent?
(NH₄)₂C₂O₄ ppts Ca²⁺ as oxalate. Here it is the unknown itself.