The direct answer
Cation Group Separation — Complete Table
| Group | Group Reagent | Cations | Precipitate Color |
|---|---|---|---|
| Group 1 | Dilute HCl | Ag⁺, Pb²⁺, Hg₂²⁺ | White (AgCl, PbCl₂, Hg₂Cl₂) |
| Group 2 | H₂S in acidic medium | Cu²⁺, Cd²⁺, Bi³⁺, Pb²⁺, Hg²⁺, As³⁺, Sb³⁺, Sn²⁺ | Black (CuS), Yellow (CdS, As₂S₃), Brown (Bi₂S₃) |
| Group 3 | NH₄OH + NH₄Cl | Fe³⁺, Al³⁺, Cr³⁺ | Red-brown (Fe(OH)₃), White (Al(OH)₃), Green (Cr(OH)₃) |
| Group 4 | H₂S in alkaline medium | Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺ | White (ZnS), Pink (MnS), Black (NiS, CoS) |
| Group 5 | (NH₄)₂CO₃ | Ba²⁺, Sr²⁺, Ca²⁺ | White (BaCO₃, SrCO₃, CaCO₃) |
| Group 6 | No group reagent | Mg²⁺, Na⁺, K⁺, NH₄⁺ | — (identified by flame test or specific tests) |
🧠 Memory trick: "Please Send Charlie's Animals To The Zoo" — Pb²⁺ (Group 1), Sn²⁺ (Group 2), Cr³⁺ (Group 3), Al³⁺ (Group 3), The (Group 4), Zn²⁺ (Group 4), Ba²⁺ (Group 5), Ca²⁺ (Group 5).
Flame Test Colors — Must Memorize
| Ion | Flame Color | JEE Tip |
|---|---|---|
| Na⁺ | Golden yellow | Most common — always tested first |
| K⁺ | Lilac / pale violet | View through cobalt glass to filter Na⁺ yellow |
| Ca²⁺ | Brick red | Distinguish from Sr²⁺ (crimson) |
| Sr²⁺ | Crimson red | Similar to Li⁺ but Li⁺ is more intense |
| Ba²⁺ | Apple green | Distinguish from Cu²⁺ (bluish green) |
| Cu²⁺ | Bluish green | Also gives blue-green with borax bead test |
| Li⁺ | Crimson | Intense red — easy to identify |
🧠 Memory trick: "Naughty Kitten Can't Stop Biting Cats" — Na (yellow), K (lilac), Ca (brick red), Sr (crimson), Ba (green), Cu (bluish green).
Common Anion Tests for JEE
| Anion | Test | Observation |
|---|---|---|
| CO₃²⁻ | Dilute HCl | Effervescence — CO₂ gas (turns lime water milky) |
| SO₄²⁻ | BaCl₂ solution | White precipitate (BaSO₄) — insoluble in HCl |
| Cl⁻ | AgNO₃ solution | White precipitate (AgCl) — soluble in NH₄OH |
| Br⁻ | AgNO₃ solution | Pale yellow precipitate (AgBr) — partially soluble in NH₄OH |
| I⁻ | AgNO₃ solution | Yellow precipitate (AgI) — insoluble in NH₄OH |
| NO₃⁻ | Brown ring test | Brown ring at junction (FeSO₄ + conc. H₂SO₄) |
| S²⁻ | Lead acetate | Black precipitate (PbS) |
| SO₃²⁻ | Dilute HCl | SO₂ gas — turns K₂Cr₂O₇ paper green |
🧠 Memory trick for AgX solubility: "Cl dissolves, Br half-dissolves, I doesn't dissolve" in NH₄OH. AgCl (white) → soluble. AgBr (pale yellow) → partially soluble. AgI (yellow) → insoluble.
Important Confirmatory Tests You Must Know
Brown Ring Test (NO₃⁻)
Add FeSO₄, then conc. H₂SO₄ along the wall. Brown ring of [Fe(H₂O)₅NO]²⁺ forms at the junction. This is a classic JEE question.
Borax Bead Test
Cu²⁺: Blue bead (oxidizing) / Red bead (reducing). Fe³⁺: Yellow-brown. Cr³⁺: Green. Mn²⁺: Violet. Co²⁺: Blue.
NH₄⁺ Test
Add NaOH and heat. NH₃ gas evolved — turns red litmus blue and gives white fumes with HCl. Also gives brown precipitate with Nessler's reagent.
Fe³⁺ Confirmatory
Add K₄[Fe(CN)₆] (potassium ferrocyanide) → Prussian blue precipitate. Or add KSCN → blood red color.
Memory Tricks for Qualitative Analysis
Group reagents in order: "HCl, H₂S, NH₄OH, H₂S, (NH₄)₂CO₃" — remember: H₂S appears twice (acidic then alkaline).
Group 2 cations: "Copper Cadmium Bismuth Lead Mercury Arsenic Antimony Tin" — CCBPLMAST (think: "Can Cows Be Pretty? Let Me Ask Some Teachers")
Group 3 cations: "Iron, Aluminum, Chromium" — IAC (think: "I Am Cool")
Group 4 cations: "Zinc, Manganese, Nickel, Cobalt" — ZMNC (think: "Zoo Monkeys Never Cry")
Group 5 cations: "Barium, Strontium, Calcium" — BSC (think: "Big Strong Cows")
Flame colors: "Naughty Kitten Can't Stop Biting Cats" — Na (yellow), K (lilac), Ca (brick red), Sr (crimson), Ba (green), Cu (bluish green)
JEE PYQ Patterns on Qualitative Analysis
| Question Type | Frequency | How to Approach |
|---|---|---|
| Identify cation from precipitate color | Very High | Match precipitate color to group and specific cation |
| Flame test identification | High | Memorize all 7 flame colors — Na, K, Ca, Sr, Ba, Cu, Li |
| Group reagent questions | High | Know which reagent precipitates which group |
| Distinguish between ions | Medium-High | Cl⁻ vs Br⁻ vs I⁻ (AgNO₃ + NH₄OH solubility), Fe²⁺ vs Fe³⁺ |
| Confirmatory test identification | Medium | Brown ring, Prussian blue, blood red (KSCN), Nessler's reagent |
| Solubility of precipitates | Medium | PbCl₂ soluble in hot water, AgCl soluble in NH₄OH |
Common JEE traps to avoid:
❌ Confusing Pb²⁺ (Group 1 AND Group 2 — it precipitates in both)
❌ Forgetting that NH₄⁺ has no group reagent (Group 6)
❌ Mixing up AgCl (white, soluble in NH₄OH) with AgBr (pale yellow, partially soluble)
❌ Not knowing that PbCl₂ is soluble in hot water
❌ Confusing flame colors of Ca²⁺ (brick red) and Sr²⁺ (crimson)
Frequently Asked Questions
What is qualitative analysis in inorganic chemistry?
Qualitative analysis is the systematic identification of cations and anions present in a salt or mixture. It uses group reagents to separate cations into groups, then confirmatory tests to identify specific ions. For JEE, you need to know the group reagents, precipitate colors, and confirmatory tests.
What are the group reagents for cation analysis?
Group 1: Dilute HCl (Ag⁺, Pb²⁺, Hg₂²⁺). Group 2: H₂S in acidic medium (Cu²⁺, Cd²⁺, Bi³⁺, Pb²⁺, Hg²⁺, As³⁺, Sb³⁺, Sn²⁺). Group 3: NH₄OH + NH₄Cl (Fe³⁺, Al³⁺, Cr³⁺). Group 4: H₂S in alkaline medium (Zn²⁺, Mn²⁺, Ni²⁺, Co²⁺). Group 5: (NH₄)₂CO₃ (Ba²⁺, Sr²⁺, Ca²⁺). Group 6: No group reagent (Mg²⁺, Na⁺, K⁺, NH₄⁺).
What are the flame test colors for JEE?
Sodium (Na⁺): Golden yellow. Potassium (K⁺): Lilac/pale violet. Calcium (Ca²⁺): Brick red. Strontium (Sr²⁺): Crimson red. Barium (Ba²⁺): Apple green. Copper (Cu²⁺): Bluish green. Lithium (Li⁺): Crimson. These are essential for JEE qualitative analysis questions.
How do I remember the cation group separation scheme?
Use the mnemonic: 'Please Send Charlie's Animals To The Zoo' — Pb²⁺ (Group 1), Sn²⁺ (Group 2), Cr³⁺ (Group 3), Zn²⁺ (Group 4), Ca²⁺ (Group 5). Or remember: 'Silver, Copper, Iron, Zinc, Barium, Magnesium' for groups 1-6 respectively.
What are common anion tests for JEE?
CO₃²⁻: Effervescence with dilute HCl (CO₂ gas). SO₄²⁻: White precipitate with BaCl₂. Cl⁻: White precipitate with AgNO₃ (soluble in NH₄OH). Br⁻: Pale yellow precipitate with AgNO₃. I⁻: Yellow precipitate with AgNO₃. NO₃⁻: Brown ring test with FeSO₄ + conc. H₂SO₄. S²⁻: Black precipitate with lead acetate.
What is the brown ring test?
The brown ring test detects nitrate (NO₃⁻) ions. Add FeSO₄ solution to the salt solution, then carefully pour concentrated H₂SO₄ along the test tube wall. A brown ring forms at the junction of the two layers due to [Fe(H₂O)₅NO]²⁺ complex formation.
Which qualitative analysis questions appear most in JEE?
JEE frequently asks: (1) Identifying the group of a cation from precipitate color, (2) Flame test colors, (3) Confirmatory tests for specific ions, (4) Distinguishing between similar ions (e.g., Cl⁻ vs Br⁻ vs I⁻), (5) Effect of group reagents, (6) Solubility of precipitates in specific reagents.
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