To systematically identify one cation and one anion present in a given salt through qualitative analysis techniques using standard laboratory procedures.
Salt analysis involves the systematic identification of cations and anions in inorganic salts. This qualitative analysis follows a scientific approach based on the chemical properties and reactions of ions.
Group I (Insoluble Chlorides): Pb²⁺, Ag⁺, Hg₂²⁺ Group II (Insoluble Sulphides): Cu²⁺, Cd²⁺, Hg²⁺, Bi³⁺, Sn²⁺, Sb³⁺ Group III (Insoluble Hydroxides): Al³⁺, Fe³⁺, Cr³⁺ Group IV (Insoluble Carbonates): Ca²⁺, Sr²⁺, Ba²⁺ Group V (Soluble Sulphides): Mg²⁺, Mn²⁺, Zn²⁺, Ni²⁺, Co²⁺, Fe²⁺
Group I (Dilute H₂SO₄ Group): CO₃²⁻, SO₃²⁻, S²⁻, NO₂⁻ Group II (Concentrated H₂SO₄ Group): Cl⁻, Br⁻, I⁻, NO₃⁻ Group III (Special Reactions): SO₄²⁻, PO₄³⁻, C₂O₄²⁻, CH₃COO⁻
Step 1: Zero Group Analysis
Step 2: Group I Analysis
Step 3: Group II Analysis
Step 4: Group III Analysis
Step 5: Group IV Analysis
Step 6: Group V Analysis
Step 1: Dilute H₂SO₄ Test
Step 2: Concentrated H₂SO₄ Test
Step 3: Special Tests
| Test | Reagent | Observation | Inference |
|---|---|---|---|
| Preliminary | Physical examination | White crystalline solid | - |
| Solubility | Water | Soluble | - |
| Group Test | Dilute HCl | No ppt | Absence of Group I |
| H₂S Test | H₂S in dil HCl | Black ppt | Presence of Group II |
| Confirmatory | K₄[Fe(CN)₆] | Chocolate ppt | Cu²⁺ confirmed |
| Test | Reagent | Observation | Inference |
|---|---|---|---|
| Dil H₂SO₄ | H₂SO₄ (dil) | Brisk effervescence | CO₃²⁻ or SO₃²⁻ |
| Gas Test | Lime water | Milky ppt | CO₂ gas, confirms CO₃²⁻ |
| Confirmatory | BaCl₂ | White ppt | CO₃²⁻ confirmed |
Cation Identified: Cu²⁺ (Copper ion)
Anion Identified: CO₃²⁻ (Carbonate ion)
Salt Identified: Copper(II) Carbonate [CuCO₃]
A: Salt analysis is based on the systematic precipitation and separation of ions using group reagents, followed by confirmatory tests for specific ions.
A: Dilute HCl is used to eliminate Group I cations (Ag⁺, Pb²⁺, Hg₂²⁺) which form insoluble chlorides.
A: Both evolve gases with dilute H₂SO₄, but CO₂ turns lime water milky permanently, while SO₂ turns acidified K₂Cr₂O₇ paper green.
A: NH₄Cl suppresses the dissociation of NH₄OH by the common ion effect, ensuring complete precipitation of Group III hydroxides.
A: In acidic medium, only Group II sulphides (CuS, CdS, etc.) precipitate, while Group III and IV sulphides remain in solution.
A: Cu²⁺ gives:
A: Clean the wire loop with conc. HCl, use non-luminous flame, and observe the color through blue glass for better results.
A: Some anions are destroyed during cation analysis (like CO₃²⁻ with HCl), so original solution ensures accurate results.
A: Using conc. H₂SO₄:
A: Systematic analysis prevents interference between ions, ensures complete separation, and provides a logical approach for accurate identification.
The systematic determination of cation and anion in a given salt requires careful observation, logical reasoning, and proper execution of analytical procedures. This experiment develops analytical skills, reinforces theoretical concepts, and provides hands-on experience with qualitative inorganic analysis techniques.
Through this comprehensive approach, students learn to identify unknown substances, understand chemical reactions, and develop scientific methodology that is fundamental to advanced chemistry studies and research applications.
This systematic approach to salt analysis forms the foundation of qualitative inorganic chemistry and is essential for various applications in environmental testing, quality control, and research laboratories.
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