Chemistry Practical Experiments Class 12 – Complete Lab Manual CBSE
Complete Chemistry practical guide for Class 12 CBSE board exams. Includes procedures, observations, precautions, and viva questions for all experiments in the CBSE syllabus.
List of Experiments (CBSE Class 12)
| Category | Experiments | Marks |
|---|---|---|
| Volumetric Analysis | Acid-base, Iodometric titrations | 8 |
| Salt Analysis | Cation & Anion identification | 8 |
| Content-based | Preparation, Tests | 6 |
| Project + Viva | Investigatory project | 8 |
Volumetric Analysis
Experiment 1: Oxalic Acid vs KMnO4 Titration
Aim
To determine the strength of a given solution of oxalic acid by titrating it against standard KMnO4 solution.
Apparatus
Burette, pipette (20 ml), conical flask, burette stand, white tile.
Chemicals
Oxalic acid solution (given), standard KMnO4, dilute H2SO4.
Theory
Reaction: 2KMnO4 + 5H2C2O4 + 3H2SO4 → K2SO4 + 2MnSO4 + 10CO2 + 8H2O
Molarity equation: M1V1/n1 = M2V2/n2
n-factor: KMnO4 = 5, Oxalic acid = 2
Procedure
- Rinse the burette with KMnO4 and fill it
- Pipette out 20 ml of oxalic acid in a conical flask
- Add 10 ml of dilute H2SO4
- Heat the solution to 60-70°C
- Titrate with KMnO4 until permanent light pink color appears
- Repeat for concordant readings
Observation Table
| S.No | Initial Reading | Final Reading | Volume of KMnO4 |
|---|---|---|---|
| 1 | 0.0 ml | 15.5 ml | 15.5 ml |
| 2 | 0.0 ml | 15.4 ml | 15.4 ml |
| 3 | 0.0 ml | 15.5 ml | 15.5 ml |
Concordant volume = 15.5 ml
Precautions
- Heat oxalic acid before titration
- Do not use indicator – KMnO4 is self-indicator
- Add KMnO4 slowly dropwise
- Titrate while solution is hot
Experiment 2: Mohr Salt vs KMnO4
Aim
To determine the percentage of iron in Mohr salt using KMnO4.
Reaction
10FeSO4 + 2KMnO4 + 8H2SO4 → 5Fe2(SO4)3 + K2SO4 + 2MnSO4 + 8H2O
Salt Analysis
Cation Analysis – Group Tests
| Group | Reagent | Cations | Observation |
|---|---|---|---|
| I | Dil. HCl | Pb2+ | White ppt |
| II | H2S + dil HCl | Cu2+, Pb2+ | Black ppt (Cu), Yellow ppt (As) |
| III | NH4Cl + NH4OH | Fe3+, Al3+ | Reddish brown (Fe), White (Al) |
| IV | H2S + NH4OH | Zn2+, Mn2+, Co2+, Ni2+ | White (Zn), Flesh colored (Mn) |
| V | (NH4)2CO3 | Ba2+, Ca2+, Sr2+ | White ppt |
| VI | No group reagent | Mg2+, Na+, K+, NH4+ | Identified by specific tests |
Anion Analysis
| Anion | Test | Observation |
|---|---|---|
| CO3²⁻ | Dil. HCl | Effervescence, gas turns lime water milky |
| SO4²⁻ | BaCl2 solution | White ppt insoluble in conc. HCl |
| Cl⁻ | AgNO3 | White ppt soluble in NH4OH |
| NO3⁻ | Ring test (FeSO4 + conc. H2SO4) | Brown ring at junction |
| S²⁻ | Lead acetate paper | Black stain |
| CH3COO⁻ | Heat with H2SO4 | Vinegar-like smell |
Sample Salt Analysis
Salt Given: FeSO4.7H2O (Ferrous Sulphate)
Physical Examination
- Color: Bluish green
- Smell: Odorless
- Solubility: Soluble in water
Dry Tests
- Heating: Loses water, turns white then brown
- Flame test: No characteristic color
Wet Tests for Cation (Fe²⁺)
- NaOH: Dirty green precipitate turning brown
- NH4OH: Dirty green ppt
- K4[Fe(CN)6]: Blue precipitate (Turnbulls blue)
Wet Tests for Anion (SO4²⁻)
- BaCl2: White precipitate insoluble in conc. HCl
- Lead acetate: White precipitate
Content-Based Experiments
Experiment: Tests for Carbohydrates
| Test | Reagent | Glucose | Sucrose | Starch |
|---|---|---|---|---|
| Molischs | α-naphthol + H2SO4 | Violet ring | Violet ring | Violet ring |
| Fehlings | Fehlings A + B | Red ppt | No reaction | No reaction |
| Benedicts | Benedicts reagent | Red/green ppt | No reaction | No reaction |
| Tollens | Ammoniacal AgNO3 | Silver mirror | No reaction | No reaction |
| Iodine | I2 solution | No change | No change | Blue color |
Experiment: Tests for Proteins
- Biuret Test: Violet color with NaOH + CuSO4
- Xanthoproteic: Yellow color with conc. HNO3
- Ninhydrin: Purple color
Experiment: Tests for Fats and Oils
- Translucent spot test: Permanent oily spot on paper
- Acrolein test: Pungent smell with KHSO4
Practical Exam Tips
- Practice titrations multiple times
- Memorize confirmatory tests for all ions
- Write observations clearly in table format
- Show all calculations step by step
- Prepare viva questions in advance
- Maintain clean apparatus
Common Viva Questions
- Why is H2SO4 added in permanganometry?
- What is the role of KMnO4 as self-indicator?
- Why is the solution heated before titration?
- Differentiate between true solution and colloidal solution
- What is the principle of paper chromatography?
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