Group Analysis for Basic Radicals (Cations) – CBSE Class 12
Introduction
Qualitative inorganic analysis involves the systematic identification of basic radicals (cations) present in a given salt or mixture. Cations are separated into six distinct groups based on the solubility of their salts with specific group reagents.
Summary Table: Cation Groups, Group Reagents, and Examples
| Group No. | Group Name | Main Group Reagent | Basic Radicals Present (Cations) | Group PPT Color / Form |
|---|---|---|---|---|
| I | Silver Group | Dilute HCl | Ag⁺, Pb²⁺, Hg₂²⁺ | White ppt. |
| II | Copper-Arsenic Group | H₂S in presence of dilute HCl | Pb²⁺, Cu²⁺, Bi³⁺, Cd²⁺, Hg²⁺, As³⁺, Sb³⁺, Sn²⁺/⁴⁺ | Colored ppt. (Black, yellow, orange-red, brown) |
| III | Aluminium-Iron Group | NH₄Cl + NH₄OH | Fe³⁺, Al³⁺, Cr³⁺ | Hydroxide ppt. (brown, white, greenish) |
| IV | Zinc Group | H₂S in presence of NH₄OH | Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺ | Sulphide ppt. (white, pink, black) |
| V | Alkaline Earth Group | (NH₄)₂CO₃ in presence of NH₄Cl + NH₄OH | Ba²⁺, Sr²⁺, Ca²⁺ | Carbonate ppt. (white) |
| VI | Magnesium Group (Last Group) | No common group reagent (confirmed by specific test) |
Mg²⁺, Na⁺, K⁺, NH₄⁺ | Variable; detected by special tests |
Group-wise Details
-
Group I (Silver Group):
- Group Reagent: Dilute HCl
- Cations Detected: Ag⁺, Pb²⁺, Hg₂²⁺
- Group PPT: White chlorides
-
Group II (Copper-Arsenic Group):
- Group Reagent: H₂S in presence of dil. HCl
- Cations Detected: Pb²⁺, Cu²⁺, Bi³⁺, Cd²⁺, Hg²⁺, As³⁺, As⁵⁺, Sb³⁺, Sn²⁺/Sn⁴⁺
- Group PPT: Colored sulphides (e.g. black, yellow)
-
Group III (Aluminium-Iron Group):
- Group Reagent: NH₄Cl + NH₄OH
- Cations Detected: Fe³⁺, Al³⁺, Cr³⁺
- Group PPT: Hydroxides (brown, white, greenish)
-
Group IV (Zinc Group):
- Group Reagent: H₂S in ammoniacal medium
- Cations Detected: Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺
- Group PPT: Sulphides (white, pink, black, brown)
-
Group V (Alkaline Earth Group):
- Group Reagent: (NH₄)₂CO₃ + NH₄Cl + NH₄OH
- Cations Detected: Ba²⁺, Sr²⁺, Ca²⁺
- Group PPT: Carbonates (white)
-
Group VI (Magnesium Group):
- Detection: No group reagent — detected by individual tests
- Cations Detected: Mg²⁺, Na⁺, K⁺, NH₄⁺
- PPT: Not formed (confirmed by specific reactions)
Notes
- Tests should be performed in correct order to avoid interferences.
- Careful washing and separation is important after each group’s ppt. is removed.
- Always confirm with specific confirmatory tests for each cation.