Class 12 Chemistry Lab Manual – Chromatography

Chromatography is an essential technique in analytical chemistry used for separating and identifying components of a mixture based on their differential migration through a stationary medium. In the Class 12 Chemistry practical syllabus, chromatography experiments typically focus on paper chromatography, where colored substances or organic compounds are separated using a solvent system. Practical examinations, conducted under the supervision of the Central Board of Secondary Education, assess students on their ability to perform experiments accurately, record observations systematically, and answer viva questions confidently.

Practical knowledge in chromatography helps students develop analytical thinking, precision in measurements, observation skills, and the ability to interpret results. Studentbro.in provides a structured, step-by-step, and exam-oriented guide to help Class 12 students master chromatography experiments.

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Importance of Chromatography in Practical Experiments

Studying chromatography in the laboratory is important because it:

• Demonstrates separation and identification of components in a mixture

• Explains the concept of stationary and mobile phases

• Develops analytical and observational skills

• Prepares students for both practical and viva examinations

• Provides insights into real-world applications in pharmaceuticals, food testing, and forensics

Hands-on experience in chromatography bridges the gap between theoretical knowledge and observable chemical behavior.

Objectives of Chromatography Experiments

The main objectives include:

• To separate components of a colored mixture using paper chromatography

• To calculate the Rf value (retardation factor) for each component

• To identify components of an unknown mixture by comparison with known samples

• To understand the influence of solvents and stationary phase on separation

• To develop precision in handling apparatus, measuring solvents, and recording observations

Achieving these objectives ensures a clear understanding of separation techniques in chemistry.

Principles of Chromatography Experiments

Chromatography experiments are based on the following principles:

• Stationary Phase – The medium that remains fixed (e.g., chromatography paper)

• Mobile Phase – The solvent that moves through the stationary phase carrying the components

• Differential Migration – Components travel at different rates due to variations in solubility and adsorption

• Rf Value (Retardation Factor) – Ratio of the distance traveled by the substance to the distance traveled by the solvent front

• Adsorption and Solubility – Governing principles for separation efficiency

Understanding these principles ensures accurate execution and interpretation of results.

Common Experiments in Chromatography

1. Separation of Components of a Colored Ink

   • Principle: Different dyes in ink move at different rates on chromatography paper depending on solubility and adsorption.

   • Apparatus: Chromatography paper, beaker, solvent, pencil, capillary tube, ruler.

   • Procedure: Draw a baseline on the paper, spot ink, suspend paper in solvent, allow solvent to rise, remove, dry, and mark solvent front.

   • Observation: Measure distances traveled by solvent and dyes, calculate Rf values.

2. Separation of Plant Pigments

   • Principle: Plant pigments like chlorophyll, carotene, and xanthophyll separate on paper chromatography due to differential solubility.

   • Apparatus: Chromatography paper, solvent mixture (petroleum ether:acetone), capillary tubes, beakers.

   • Procedure: Spot plant extract, allow solvent to travel, dry paper, measure distances.

   • Observation: Identify pigments by color and calculate Rf values.

3. Identification of Unknown Components

   • Principle: Compare Rf values of unknown samples with standards to identify chemical components.

   • Apparatus: Chromatography setup as above, standard compounds.

   • Procedure: Perform chromatography for both unknown and known samples, compare Rf values.

   • Observation: Determine the identity of unknown substances.

These experiments provide practical understanding of the principles of separation and identification of compounds.

Apparatus Required for Chromatography

• Chromatography paper

• Beakers or jars

• Solvents (water, acetone, petroleum ether, alcohol)

• Capillary tubes for spotting

• Pencil for marking baseline

• Ruler for measuring distances

• Gloves, goggles, and lab coat

Familiarity with apparatus ensures precise and safe execution of experiments.

Experimental Setup

• Fold chromatography paper to form a strip or use plain rectangular sheets

• Mark a baseline using pencil, not ink

• Spot sample with a capillary tube carefully

• Place paper in a beaker with solvent level below the baseline

• Allow solvent to rise undisturbed

• Remove and dry paper once solvent front reaches desired height

• Mark solvent front immediately for accurate Rf calculation

Proper setup ensures accurate separation and reproducibility of results.

Observation Tables and Recording Results

Observation tables include:

• Name of substance or ink

• Color of each component after separation

• Distance traveled by solvent front (cm)

• Distance traveled by each component (cm)

• Calculated Rf value

Systematic recording is essential for analysis and viva preparation.

Calculations and Results

Students should:

• Calculate Rf values using the formula:

Rf=Distance traveled by substanceDistance traveled by solvent frontRf = \frac{\text{Distance traveled by substance}}{\text{Distance traveled by solvent front}}Rf=Distance traveled by solvent frontDistance traveled by substance​

• Compare Rf values with standard references

• Identify unknown components

• Record results systematically for clarity

Accurate calculations strengthen understanding and practical skills.

Precautions for Chromatography Experiments

• Use pencil, not ink, for baseline

• Ensure solvent level is below the sample spot

• Do not disturb beaker during solvent migration

• Use fresh solvents for better separation

• Dry paper carefully to avoid smudging

• Wear gloves, goggles, and lab coat

Precautions ensure safety, accuracy, and reproducibility.

Common Mistakes to Avoid

• Spotting samples too large or thick

• Solvent level above the baseline

• Disturbing the beaker while solvent rises

• Not marking solvent front immediately

• Using contaminated or impure solvent

Avoiding mistakes ensures reliable results and maximum marks.

Viva Questions on Chromatography

• What is chromatography and its principle?

• Define stationary and mobile phases

• How is Rf value calculated?

• Why is pencil used for baseline instead of ink?

• Explain separation of components in plant pigments

• What precautions are necessary in chromatography experiments?

Preparing for viva helps students answer confidently during practical exams.

Marking Scheme for Chromatography Practical

Marks are awarded based on:

• Correct experimental setup and procedure

• Accuracy of measurements and Rf calculations

• Identification of components correctly

• Neat diagrams and recorded tables

• Completion of practical record

• Viva answers

A complete and well-documented report ensures maximum marks.

Applications of Chromatography

Chromatography is widely used in:

• Pharmaceutical industry for drug purity testing

• Food industry for identifying additives and dyes

• Forensic science for analyzing ink and pigments

• Environmental analysis for detecting pollutants

• Biochemistry for separating biomolecules like amino acids and pigments

Practical knowledge connects laboratory experiments with real-world applications.

How Studentbro.in Supports Class 12 Chemistry Students

Studentbro.in provides:

• Step-by-step guidance for chromatography experiments

• Apparatus handling and setup instructions

• Observation table templates and calculation examples

• Viva question bank and preparation strategies

• Safety and precaution tips aligned with CBSE syllabus

Our resources equip students with structured, reliable, and exam-focused preparation.

Conclusion

Chromatography experiments are crucial for understanding separation and identification of chemical mixtures. Accurate spotting, systematic observation, precise calculation, and careful handling of apparatus are key to performing well in practical examinations.

By following CBSE guidelines and regular practice, students can confidently perform chromatography experiments and achieve excellent results.

Studentbro.in provides comprehensive, easy-to-understand, and exam-oriented resources to support Class 12 students in mastering Chemistry practicals.