Salt Analysis: Copper(II) Sulphate (CuSO₄)
Salt Analysis: Copper(II) Sulphate (CuSO4)
1. Physical Examination of the Salt
| Experiment |
Observation |
Inference |
| Colour |
Blue |
Cu or Ni salt may be present |
| Smell |
No characteristic smell observed |
Inconclusive |
| Deliquescence |
Does not absorb moisture from air |
Non-deliquescent |
2. Dry Heating Test
| Experiment |
Observation |
Inference |
| A pinch of salt is taken in a dry test tube and heated. |
The color of salt turns white and suffocating smell is observed. |
CuSO4 may be present |
3. Flame Test
| Experiment |
Observation |
Inference |
| A clean platinum wire dipped in conc. HCl is touched with the salt and held at the edge of the oxidizing flame of a Bunsen burner. |
Brilliant green flame observed |
Cu2+ may be present |
4. Concentrated H2SO4 Test
| Experiment |
Observation |
Inference |
| A pinch of salt is heated with 2 drops of conc. H2SO4. |
Colourless gas with suffocating smell observed |
Chloride or sulphate may be present |
5. Wet Test for Acid Radical (Sulphate Ion, SO₄²⁻)
| Experiment |
Observation |
Inference |
| To the aqueous solution of salt, BaCl2 solution is added. |
White precipitate observed, which is insoluble in dilute HCl. |
Presence of sulphate ion confirmed |
Reaction:
SO42− + BaCl2 → BaSO4↓ + 2Cl−
6. Test for Basic Radical (Copper Ion, Cu²⁺)
| Experiment |
Observation |
Inference |
| To salt, NaOH solution is added and warmed. |
No ammoniacal smell observed. |
NH4+ ion is absent |
| Add dilute HCl to aqueous solution of salt, pass H2S gas. |
Black precipitate observed. |
Group II elements present |
| Black ppt. is dissolved in 1:1 HNO3. Ammonium hydroxide added. |
Blue solution observed |
Group IIIB is present |
| Blue solution acidified with acetic acid, potassium ferrocyanide solution added. |
Chocolate brown precipitate of copper ferrocyanide observed |
Cu2+ ion confirmed |
Reaction:
2Cu2+ + K4Fe(CN)6 → Cu2[Fe(CN)6] (chocolate brown ppt) + 4K+
Conclusion
Acid Radical: SO42− (Sulphate ion)
Basic Radical: Cu2+ (Copper ion)