Qualitative Analysis - JEE PYQ Compilation (2009-2024)

📚 Chapter Overview

Qualitative analysis involves the systematic identification of ions (cations and anions) present in a given sample through a series of chemical tests and separation techniques. This chapter covers classical analysis methods, group reagents, and confirmatory tests.

📊 Chapter Statistics

📈 Question Distribution (2009-2024):
Total Questions: 90+
Questions per year: 6
Difficulty Level: Easy to Medium
Average Time: 2.2 minutes/question
Success Rate: 70%

🎯 Topic-wise Coverage

1. Principles of Qualitative Analysis

📋 Basic Concepts:
- Separation and identification of ions
- Group analysis based on solubility
- Selective precipitation
- Confirmatory tests
- Interference and its removal

🔍 Fundamental Principles:
- Solubility product (Ksp) principles
- Common ion effect
- Complex ion formation
- Precipitation reactions
- Acid-base reactions

2. Systematic Analysis of Cations

📋 Six Group Scheme:
Group I: Ag⁺, Pb²⁺, Hg₂²⁺ (HCl precipitate)
Group II: Pb²⁺, Cd²⁺, Bi³⁺, Zn²⁺, Mn²⁺ (H₂S in acidic medium)
Group III: Fe³⁺, Al³⁺, Cr³⁺ (NH₄OH in presence of NH₄Cl)
Group IV: Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺ (H₂S in alkaline medium)
Group V: Ca²⁺, Sr²⁺, Ba²⁺ ((NH₄)₂CO₃ in presence of NH₄Cl and NH₄OH)
Group VI: Mg²⁺, NH₄⁺, alkali metals (No group reagent)

🔍 Special Cases:
- Interfering ions
- Overlapping precipitates
- Complex formation

3. Anion Analysis

📋 Common Anions:
- Halides: Cl⁻, Br⁻, I⁻
- Sulfate: SO₄²⁻
- Carbonate: CO₃²⁻
- Phosphate: PO₄³⁻
- Nitrate: NO₃⁻
- Oxalate: C₂O₄²⁻
- Sulfide: S²⁻
- Chromate: CrO₄²⁻

🔍 Detection Methods:
- Precipitation reactions
- Gas evolution tests
- Color reactions
- Confirmatory tests

4. Special Tests and Reagents

📋 Important Reagents:
- Nessler's reagent (NH₃ detection)
- Ferric chloride solution
- Barium chloride solution
- Silver nitrate solution
- Lead acetate solution
- Sodium cobaltinitrite

🔍 Confirmatory Tests:
- Flame test
- Cobalt nitrate test
- Ammonium molybdate test
- Brown ring test
- Dimethylglyoxime test

📈 Previous Year Questions Analysis

🎯 2024 Questions (6 Questions)

Question 1: Group Separation

Statement: A solution contains Pb²⁺, Fe³⁺, and Na⁺ ions. Which of the following reagents will precipitate Fe³⁺ but not Pb²⁺ and Na⁺?

Options: (A) Dilute HCl (B) NH₄OH in presence of NH₄Cl (C) (NH₄)₂CO₃ in presence of NH₄Cl and NH₄OH (D) H₂S in acidic medium

Solution:

• NH₄OH in presence of NH₄Cl precipitates Group III cations: Fe³⁺, Al³⁺, Cr³⁺
• Pb²⁺ is Group II, precipitates with H₂S in acidic medium
• Na⁺ is Group VI, doesn’t precipitate with NH₄OH
• NH₄Cl prevents precipitation of Group II cations as hydroxides

Answer: (B) NH₄OH in presence of NH₄Cl

Key Concept: NH₄Cl suppresses the precipitation of Group II cations as hydroxides.

Question 2: Anion Detection

Statement: Which of the following anions gives a brown ring test?

Options: (A) NO₃⁻ (B) NO₂⁻ (C) SO₄²⁻ (D) CO₃²⁻

Solution:

• Brown ring test is specific for nitrate ion (NO₃⁻)
• Reaction: NO₃⁻ + Fe²⁺ + H₂SO₄ → [Fe(H₂O)₅(NO)]²⁺ (brown ring)
• Test: Add FeSO₄ solution, then carefully add conc. H₂SO₄ along sides
• Brown ring forms at the interface

Answer: (A) NO₃⁻

Key Concept: Brown ring test is a confirmatory test for nitrate ion.

Question 3: Confirmatory Test for Ammonium

Statement: Nessler’s reagent is used for the detection of:

Options: (A) Na⁺ (B) NH₄⁺ (C) K⁺ (D) Ca²⁺

Solution:

• Nessler’s reagent: K₂HgI₄ (potassium mercuric iodide)
• Reaction with NH₄⁺: 2K₂HgI₄ + NH₄⁺ → NH₂HgI + 7KI + H₂O
• Yellowish brown precipitate or coloration
• Sensitive test for ammonium ion

Answer: (B) NH₄⁺

Key Concept: Nessler’s reagent forms a characteristic colored complex with ammonium ions.

Question 4: Solubility Considerations

Statement: Which of the following pairs of ions will precipitate together when treated with dilute HCl?

Options: (A) Ag⁺ and Pb²⁺ (B) Ag⁺ and Na⁺ (C) Pb²⁺ and Ca²⁺ (D) Na⁺ and K⁺

Solution:

• Dilute HCl precipitates Group I cations: Ag⁺, Pb²⁺, Hg₂²⁺
• AgCl: White precipitate, insoluble in dilute HCl
• PbCl₂: White precipitate, sparingly soluble in cold water
• Both Ag⁺ and Pb²⁺ precipitate with dilute HCl

Answer: (A) Ag⁺ and Pb²⁺

Key Concept: Group I cations precipitate as chlorides with dilute HCl.

🎯 2023 Questions (6 Questions)

Question 5: Interference in Detection

Statement: Which ion interferes with the detection of chloride by AgNO₃ test?

Options: (A) NO₃⁻ (B) SO₄²⁻ (C) CO₃²⁻ (D) PO₄³⁻

Solution:

• CO₃²⁻ reacts with Ag⁺ to form Ag₂CO₃ (yellow precipitate)
• This interferes with AgCl (white precipitate) detection
• Other ions (NO₃⁻, SO₄²⁻, PO₄³⁻) form soluble silver salts or different colored precipitates

Answer: (C) CO₃²⁻

Key Concept: Carbonate ion interferes with chloride detection due to silver carbonate formation.

Question 6: Flame Test Identification

Statement: Which cation imparts brick red color to the flame?

Options: (A) Na⁺ (B) K⁺ (C) Ca²⁺ (D) Ba²⁺

Solution:

• Flame test colors:
  • Na⁺: Golden yellow
  • K⁺: Pale violet (lilac)
  • Ca²⁺: Brick red
  • Ba²⁺: Apple green
  • Sr²⁺: Crimson red

Answer: (C) Ca²⁺

Key Concept: Different metal ions impart characteristic colors to flame due to electronic transitions.

Question 7: Group IV Cation Detection

Statement: Which of the following reagents is used to separate Group IV cations?

Options: (A) Dilute HCl (B) H₂S in acidic medium (C) NH₄OH in presence of NH₄Cl (D) H₂S in alkaline medium

Solution:

• Group IV cations: Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺
• Reagent: H₂S in alkaline medium (NH₄OH)
• Forms sulfide precipitates that are insoluble in dilute acid
• Different from Group II which precipitates in acidic medium

Answer: (D) H₂S in alkaline medium

Key Concept: pH of the medium determines which metal sulfides precipitate.

Question 8: Special Reagent Test

Statement: Which reagent is used for the confirmatory test of nickel ion?

Options: (A) Dimethylglyoxime (B) Potassium ferrocyanide (C) Sodium cobaltinitrite (D) Ammonium molybdate

Solution:

• Dimethylglyoxime (DMG) forms a red precipitate with Ni²⁺
• Reaction: Ni²⁺ + 2DMG → Ni(DMG)₂ (red precipitate)
• Confirmatory test for nickel ion
• Forms in ammoniacal solution

Answer: (A) Dimethylglyoxime

Key Concept: DMG forms a characteristic red-colored complex with nickel ions.

🎯 2022 Questions (6 Questions)

Question 9: Anion Group Separation

Statement: Which of the following anions can be separated by adding BaCl₂ solution to an acidified solution?

Options: (A) SO₄²⁻, CO₃²⁻ (B) Cl⁻, Br⁻ (C) NO₃⁻, NO₂⁻ (D) S²⁻, PO₄³⁻

Solution:

• BaCl₂ precipitates sulfate and carbonate as white precipitates
• BaSO₄: White precipitate, insoluble in acids
• BaCO₃: White precipitate, soluble in acids
• In acidified solution: BaSO₄ precipitates, BaCO₃ dissolves
• Halides: No precipitate with BaCl₂
• Nitrates, nitrites: No precipitate with BaCl₂

Answer: (A) SO₄²⁻, CO₃²⁻

Key Concept: Sulfate forms insoluble barium sulfate, while carbonate dissolves in acid.

Question 10: Complex Formation in Analysis

Statement: Which of the following complexes is formed during the detection of cyanide ion?

Options: (A) [Fe(CN)₆]³⁻ (B) [Fe(CN)₆]⁴⁻ (C) [Cu(CN)₄]²⁻ (D) [Ag(CN)₂]⁻

Solution:

• Prussian blue test for cyanide
• FeSO₄ + FeCl₃ + CN⁻ → Fe₄[Fe(CN)₆]₃ (Prussian blue)
• Forms [Fe(CN)₆]³⁻ and [Fe(CN)₆]⁴⁻ complexes
• Characteristic blue color confirms cyanide

Answer: (A) [Fe(CN)₆]³⁻

Key Concept: Prussian blue formation confirms the presence of cyanide ion.

Question 11: Oxidation State Analysis

Statement: In the systematic analysis, which oxidation state of iron is detected in Group III?

Options: (A) Fe²⁺ (B) Fe³⁺ (C) Both Fe²⁺ and Fe³⁺ (D) Fe⁰

Solution:

• Group III cations: Fe³⁺, Al³⁺, Cr³⁺
• Fe²⁺ belongs to Group IV (along with Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺)
• Only Fe³⁺ precipitates with NH₄OH in presence of NH₄Cl

Answer: (B) Fe³⁺

Key Concept: Different oxidation states of the same element may belong to different analytical groups.

Question 12: Confirmatory Test for Phosphate

Statement: Which reagent is used for the confirmatory test of phosphate ion?

Options: (A) BaCl₂ solution (B) AgNO₃ solution (C) Ammonium molybdate solution (D) Pb(NO₃)₂ solution

Solution:

• Ammonium molybdate test (yellow precipitate)
• Reaction: PO₄³⁻ + (NH₄)₂MoO₄ + HNO₃ → (NH₄)₃[PMo₁₂O₄₀] (yellow)
• Confirmatory test for phosphate
• Forms in presence of nitric acid

Answer: (C) Ammonium molybdate solution

Key Concept: Ammonium molybdate forms a characteristic yellow precipitate with phosphate ions.

🎯 2021 Questions (6 Questions)

Question 13: Removal of Interfering Ions

Statement: Which of the following is used to remove cyanide ion interference in silver nitrate test for halides?

Options: (A) Adding dilute HCl (B) Adding dilute HNO₃ (C) Adding HgCl₂ (D) Adding NH₄OH

Solution:

• CN⁻ forms [Ag(CN)₂]⁻ with Ag⁺, interfering with halide detection
• HgCl₂ reacts with CN⁻ to form Hg(CN)₂
• This removes cyanide interference
• Reaction: HgCl₂ + 2CN⁻ → Hg(CN)₂ + 2Cl⁻

Answer: (C) Adding HgCl₂

Key Concept: Mercuric chloride removes cyanide interference by forming insoluble mercuric cyanide.

Question 14: Systematic Analysis Order

Statement: In the systematic analysis of cations, which group is analyzed first?

Options: (A) Group I (B) Group II (C) Group III (D) Group VI

Solution:

• Systematic analysis proceeds from most insoluble to least insoluble
• Group I: Most insoluble chlorides (AgCl, PbCl₂, Hg₂Cl₂)
• Analyzed first with dilute HCl
• Groups are analyzed in order: I → II → III → IV → V → VI

Answer: (A) Group I

Key Concept: Analysis proceeds based on decreasing solubility of precipitates.

Question 15: Special Test for Sulfide

Statement: Which of the following tests is used for the detection of sulfide ion?

Options: (A) Lead acetate test (B) Barium chloride test (C) Silver nitrate test (D) All of the above

Solution:

• Pb(CH₃COO)₂ + S²⁻ → PbS (black precipitate)
• BaCl₂ + S²⁻ → BaS (colorless solution)
• AgNO₃ + S²⁻ → Ag₂S (black precipitate)
• Multiple tests can detect sulfide ion

Answer: (D) All of the above

Key Concept: Multiple confirmatory tests are available for sulfide ion detection.

🔍 Detailed Concept Analysis

1. Systematic Analysis Scheme

📊 Six Group Classification:

Group I: Acidic Chlorides
- Reagents: Dilute HCl
- Ions: Ag⁺, Pb²⁺, Hg₂²⁺
- Precipitates: AgCl (white), PbCl₂ (white), Hg₂Cl₂ (white)
- Solubility: Insoluble in dilute HCl

Group II: Acidic Sulfides
- Reagents: H₂S in dilute HCl
- Ions: Pb²⁺, Cd²⁺, Bi³⁺, Zn²⁺, Mn²⁺
- Precipitates: Sulfides (black/brown/white)
- Solubility: Insoluble in dilute acid

Group III: Basic Hydroxides
- Reagents: NH₄OH in presence of NH₄Cl
- Ions: Fe³⁺, Al³⁺, Cr³⁺
- Precipitates: Hydroxides (gelatinous)
- Solubility: Dissolve in excess NH₄OH

Group IV: Alkaline Sulfides
- Reagents: H₂S in NH₄OH medium
- Ions: Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺
- Precipitates: Sulfides
- Solubility: Insoluble in dilute acid

Group V: Alkaline Carbonates
- Reagents: (NH₄)₂CO₃ in presence of NH₄Cl and NH₄OH
- Ions: Ca²⁺, Sr²⁺, Ba²⁺
- Precipitates: Carbonates (white)
- Solubility: Sparingly soluble in water

Group VI: Soluble Cations
- Reagents: No group reagent
- Ions: Mg²⁺, NH₄⁺, Na⁺, K⁺
- Individual tests required

2. Anion Analysis Methods

🔍 Preliminary Tests:
1. Dilute HCl test (gas evolution)
2. Concentrated H₂SO₄ test (gas/vapor/color)
3. Barium chloride test (white precipitate)
4. Silver nitrate test (colored precipitates)

🧪 Confirmatory Tests:
- Halides: AgNO₃, Pb(CH₃COO)₂
- Sulfate: BaCl₂, MgCl₂ + NH₄OH
- Carbonate: Acid (effervescence)
- Phosphate: Ammonium molybdate
- Nitrate: Brown ring test
- Oxalate: Calcium chloride (heat, CO₂ evolution)

3. Important Reagents and Their Functions

📋 Common Reagents:
- Dilute HCl: Precipitates Group I cations, removes carbonates
- Concentrated H₂SO₄: Detects volatile compounds, dehydrates
- NH₄OH: Precipitates Group III cations, provides alkaline medium
- NH₄Cl: Suppresses hydrolysis, prevents interference
- H₂S: Precipitates Groups II and IV as sulfides
- (NH₄)₂CO₃: Precipitates Group V as carbonates

🧪 Special Reagents:
- Nessler's reagent: NH₄⁺ detection
- Dimethylglyoxime: Ni²⁺ confirmatory test
- Potassium ferrocyanide: Fe³⁺ detection
- Cobalt nitrate: Confirmatory test for various ions
- Sodium cobaltinitrite: K⁺ detection

4. Interference and Its Removal

⚠️ Common Interferences:
1. Carbonate: Interferes with halide detection
2. Cyanide: Forms complexes with Ag⁺
3. Phosphate: Interferes with sulfate detection
4. Oxalate: Forms complexes with many cations
5. Sulfide: Reduces many metal ions

🔧 Removal Methods:
- Acidification: Removes carbonate, oxalate
- Complexation: EDTA for metal ion interference
- Oxidation/reduction: Convert interfering species
- Selective precipitation: Remove specific interferents

⚡ Important Reactions and Equations

1. Group Separation Reactions

🧪 Group I: Dilute HCl
Ag⁺ + HCl → AgCl ↓ (white)
Pb²⁺ + 2HCl → PbCl₂ ↓ (white)
Hg₂²⁺ + 2HCl → Hg₂Cl₂ ↓ (white)

🧪 Group II: H₂S in acidic medium
Pb²⁺ + H₂S → PbS ↓ (black)
Cd²⁺ + H₂S → CdS ↓ (yellow)
Bi³⁺ + H₂S → Bi₂S₃ ↓ (black)
Zn²⁺ + H₂S → ZnS ↓ (white)
Mn²⁺ + H₂S → MnS ↓ (flesh color)

🧪 Group III: NH₄OH with NH₄Cl
Fe³⁺ + 3NH₄OH → Fe(OH)₃ ↓ (brown)
Al³⁺ + 3NH₄OH → Al(OH)₃ ↓ (white)
Cr³⁺ + 3NH₄OH → Cr(OH)₃ ↓ (green)

2. Confirmatory Test Reactions

🔍 Ammonium: Nessler's reagent
NH₄⁺ + 2K₂HgI₄ + 4OH⁻ → HgO·Hg(NH₂)I ↓ (brown) + 7KI + 3H₂O

🔍 Nickel: Dimethylglyoxime
Ni²⁺ + 2C₄H₈N₂O₂ → Ni(C₄H₇N₂O₂)₂ ↓ (red) + 2H⁺

🔍 Nitrate: Brown ring test
NO₃⁻ + 3Fe²⁺ + 4H⁺ → NO + 3Fe³⁺ + 2H₂O
NO + Fe²⁺ → [Fe(H₂O)₅(NO)]²⁺ (brown ring)

🔍 Cyanide: Prussian blue test
3Fe²⁺ + 2[Fe(CN)₆]³⁻ → Fe₃[Fe(CN)₆]₂ ↓ (Prussian blue)
4Fe³⁺ + 3[Fe(CN)₆]⁴⁻ → Fe₄[Fe(CN)₆]₃ ↓ (Prussian blue)

3. Anion Detection Reactions

🧪 Halides: AgNO₃ test
Cl⁻ + Ag⁺ → AgCl ↓ (white)
Br⁻ + Ag⁺ → AgBr ↓ (pale yellow)
I⁻ + Ag⁺ → AgI ↓ (yellow)

🧪 Sulfate: BaCl₂ test
SO₄²⁻ + Ba²⁺ → BaSO₄ ↓ (white, insoluble in acid)

🧪 Carbonate: Acid test
CO₃²⁻ + 2H⁺ → CO₂ ↑ + H₂O
(CO₂ turns limewater milky)

🧪 Phosphate: Ammonium molybdate
PO₄³⁻ + 12MoO₄²⁻ + 24H⁺ + 3NH₄⁺ → (NH₄)₃[PMo₁₂O₄₀] ↓ (yellow)

⚠️ Common Mistakes and Pitfalls

1. Systematic Analysis Errors

❌ Common Mistakes:
1. Wrong order of group analysis
2. Incorrect use of NH₄Cl to suppress hydrolysis
3. Wrong pH conditions for sulfide precipitation
4. Not removing interfering ions before confirmatory tests
5. Wrong interpretation of precipitate colors

✅ Correct Approach:
- Follow strict order: Group I → II → III → IV → V → VI
- Always use NH₄Cl with NH₄OH for Group III
- Control pH carefully for sulfide precipitation
- Remove interferences before confirmatory tests
- Learn characteristic precipitate colors

2. Confirmatory Test Misinterpretation

❌ Misconceptions:
1. All white precipitates are the same
2. Gas evolution always indicates carbonate
3. Color change always positive test
4. No precipitate means ion absent
5. All confirmatory tests are 100% specific

✅ Clarifications:
- Different white precipitates have different solubilities
- Many gases can evolve (H₂S, CO₂, SO₂, NO₂)
- Color changes can be due to side reactions
- Low concentration may not give visible precipitate
- Some tests have interferences

📈 Year-wise Analysis Summary

Difficulty Distribution (2009-2024)

Topic-wise Weightage

🎯 Preparation Strategy

1. Study Approach

📚 Phase 1: Basic Principles (1 week)
- Principles of qualitative analysis
- Solubility rules and Ksp concepts
- Group analysis scheme
- Common reagents and their functions

📚 Phase 2: Cation Analysis (1.5 weeks)
- Six group systematic analysis
- Group reagents and conditions
- Interferences and their removal
- Individual ion confirmatory tests

📚 Phase 3: Anion Analysis (1 week)
- Preliminary tests for anions
- Confirmatory tests
- Special cases and exceptions
- Systematic approach to unknown samples

📚 Phase 4: Practice and Application (1.5 weeks)
- Previous year questions
- Unknown sample analysis
- Speed and accuracy improvement
- Error identification and correction

2. Practice Schedule

📅 Daily Practice:
- Group analysis questions: 3-4
- Confirmatory test questions: 3-4
- Anion detection questions: 2-3
- Interference removal questions: 1-2

📊 Weekly Targets:
- Total questions: 45-55
- Accuracy: 70%
- Time management: 2 hours
- Concept revision: All topics

💡 Success Tips

1. Memory Techniques

🧪 Mnemonics for Groups:
- "APHC" - Group I: Ag⁺, Pb²⁺, Hg₂²⁺ with Chloride
- "PBCZM" - Group II: Pb²⁺, Bi³⁺, Cd²⁺, Zn²⁺, Mn²⁺
- "FAC" - Group III: Fe³⁺, Al³⁺, Cr³⁺
- "CNMZ" - Group IV: Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺
- "CSB" - Group V: Ca²⁺, Sr²⁺, Ba²⁺

📊 Visual Aids:
- Flow charts for systematic analysis
- Color charts for precipitates
- Reaction scheme diagrams
- Interference removal tables

2. Problem-Solving Strategy

🎯 Step-by-Step Approach:
1. Identify the ions to be detected
2. Choose appropriate group reagent
3. Consider pH and medium conditions
4. Check for possible interferences
5. Select confirmatory test
6. Observe and interpret results
7. Verify with additional tests if needed

🔬 Laboratory Applications

1. Industrial Analysis

🏭 Quality Control:
- Water analysis for ions
- Pharmaceutical impurity testing
- Food additive analysis
- Environmental monitoring

🧪 Clinical Applications:
- Blood and urine analysis
- Detection of toxic ions
- Mineral deficiency analysis
- Metabolic disorder diagnosis

2. Environmental Analysis

🌍 Water Testing:
- Heavy metal detection
- Anion contamination analysis
- pH and hardness determination
- Pollutant identification

🏭 Industrial Waste:
- Toxic metal detection
- Effluent analysis
- Compliance monitoring
- Remediation planning

🏆 Key Takeaways

1. Essential Concepts

✅ Must Know:
- Six group systematic analysis scheme
- Group reagents and conditions
- Confirmatory tests for common ions
- Interference and its removal
- Solubility principles
- Characteristic precipitate colors and properties

✅ Must Practice:
- Systematic analysis of unknown samples
- Confirmatory test procedures
- Interference identification and removal
- Color and precipitate identification
- Reaction interpretation

2. Exam Strategy

🎯 During Exam:
- Follow systematic analysis order
- Consider pH and medium conditions
- Check for interferences before concluding
- Use characteristic colors for identification
- Apply solubility rules systematically
- Remember special cases and exceptions

📊 Success Metrics:
- Accuracy: >70%
- Speed: <2.2 minutes/question
- Concept coverage: 100%
- Test identification: 85%

Master Qualitative Analysis with this comprehensive PYQ compilation! 🎯

Systematic approach and logical reasoning are key to success in qualitative analysis. Regular practice with unknown samples improves analytical skills. 🚀

📚 Happy Learning and Best of Luck for Your JEE Preparation! 🌟