Step-by-Step Paper Chromatography Experiment and How It Works
Paper chromatography is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
What is Paper Chromatography in Chemistry?
A paper chromatography refers to a simple and effective separation technique used in chemistry to separate and identify components of a mixture using special filter paper as a stationary phase and a solvent as a mobile phase.
This concept appears in chapters related to separation of mixtures, polarity, and analytical methods, making it a foundational part of your chemistry syllabus.
Preparation and Synthesis Methods
- Paper chromatography does not involve the synthesis of any new chemical but is a practical lab method.
- The main preparation involves choosing a suitable filter paper, preparing a sample solution, and selecting an appropriate solvent (or solvent mixture) as the mobile phase.
- The sample is spotted near the base of the paper and allowed to develop in a closed chamber until the solvent front rises sufficiently, carrying the separated components with it at different rates.
Physical Properties of Paper Chromatography (Optional)
- The process involves a filter paper strip (usually white and absorbent), a sample spot about 1–2 cm above the base, and a colorless or colored solvent.
- Solubility of the sample, capillary action of the paper, and temperature can affect the separation.
- The sample can be colored (like ink or plant pigments) or colorless (developed afterward using reagents).
Chemical Properties and Reactions
- No chemical change takes place in paper chromatography.
- It works based on the differences in adsorption and partition coefficients of sample components between the paper (stationary phase) and the solvent (mobile phase).
- Some samples may react with specific color-developing chemicals after separation to make them visible.
Frequent Related Errors
- Believing paper chromatography can separate all compounds, even if they have very similar properties.
- Applying a thick or uneven starting spot, causing poor separation.
- Letting the starting spot dip into the solvent (sample washes away before separation begins).
- Using inappropriate or impure solvents, leading to unclear chromatograms.
Uses of Paper Chromatography in Real Life
Paper chromatography is widely used in food testing (to identify dyes in sweets or jams), forensic analysis (to detect substances in criminal investigations), pharmaceutical testing, and separation of plant pigments. It is also one of the best techniques to introduce students to the world of analytical chemistry.
Relation with Other Chemistry Concepts
Paper chromatography is closely related to topics such as separation techniques and mixtures, helping students build a conceptual bridge between various chapters. The concept of polarity covered in polar compounds plays a vital role, as more polar substances travel less on polar (water-based) papers.
Step-by-Step Reaction Example
1. Draw a horizontal line about 2 cm from the base of a filter paper. Place a small spot of ink or sample on it and allow it to dry.2. Pour a small amount of solvent (like water or alcohol) into a beaker, just enough to cover the base.
3. Suspend the paper strip in the beaker so the spot is above the solvent level, and cover the beaker.
4. Allow the solvent to rise up the paper, separating the components into colored bands or spots.
5. Mark the solvent front when finished, and measure the distance traveled by the solvent and each sample component.
Lab or Experimental Tips
Always check that the starting spot is dry and above the solvent level before you start. Use a pencil, not ink, to mark lines, so it doesn’t dissolve. Vedantu educators often use rainbow or plant pigment experiments to make this concept easy and visual for students.
Try This Yourself
- Calculate the Rf value if a dye spot travels 5 cm and the solvent front is 10 cm from the origin.
- Try separating different marker pen colors using water and compare the results.
- Identify which component is most strongly adsorbed to the paper and which moves furthest.
Final Wrap-Up
We explored paper chromatography—its setup, principle, uses, and common errors. This method highlights how simple materials can separate complex mixtures. For more detailed explanations and exam-oriented learning, explore live classes and topic notes on Vedantu.
Mixtures
Polar Compounds
Rf Value
FAQs on Paper Chromatography: Principle, Procedure, and Applications
1. What is paper chromatography?
Paper chromatography is an analytical technique used to separate and identify components of a mixture using absorbent paper and a solvent. The sample travels along the paper due to capillary action, and each component moves at a different rate based on its polarity and solubility.
2. What are the phases involved in paper chromatography?
Paper chromatography uses two main phases:
- Stationary phase: Filter paper or chromatography paper that absorbs the solvent.
- Mobile phase: The solvent (such as water or alcohol) that moves through the paper carrying the mixture components.
3. What is the principle behind paper chromatography?
Paper chromatography works on the principle of partition chromatography, where substances separate based on their relative solubility and adsorption between the mobile phase (solvent) and the stationary phase (paper). Components with higher solubility in the mobile phase travel further, while those with greater adsorption to the stationary phase move less.
4. What is an Rf value and how is it calculated?
The Rf value (retention factor) measures how far a substance travels on the chromatography paper relative to the solvent:
- Rf = Distance moved by substance ÷ Distance moved by solvent front
- The value ranges from 0 to 1, unique for each compound under specific conditions.
5. Why do different colours or spots appear during paper chromatography?
Colours or spots appear as a result of different components in the mixture separating due to variations in polarity, solubility, and affinity for the stationary and mobile phases. Each component travels a different distance, forming distinct coloured or visible spots on the paper.
6. What are the main steps in conducting a paper chromatography experiment?
Follow these steps for a paper chromatography experiment:
- Draw a baseline on chromatography paper and spot the sample mixture.
- Place the paper in a container with solvent, ensuring the sample is above the solvent level.
- The solvent rises by capillary action, carrying different components at various rates.
- Remove the paper when the solvent front nears the top and mark the solvent front immediately.
- Observe and measure the separated spots for analysis.
7. What are the uses and applications of paper chromatography?
Paper chromatography is widely used for:
- Separation and identification of amino acids, sugars, and plant pigments
- Detecting adulteration in foods
- Analysis of inks or dyes
- Forensic science for analyzing substances
- Pharmaceutical research and purity testing
8. What are the advantages and limitations of paper chromatography?
Advantages:
- Simple, cost-effective, and quick
- Requires minimal equipment and small sample size
Limitations:
- Less suitable for non-polar or volatile compounds
- Lower separation efficiency compared to advanced techniques
9. Can paper chromatography be used for colourless compounds? If so, how are the spots visualized?
Yes, paper chromatography can be used for colourless compounds. Spots can be visualized using techniques such as:
- UV light exposure
- Spraying with specific reagents that develop colour
- Staining agents for biological samples
10. What factors affect the separation of components in paper chromatography?
Several factors influence separation:
- Solvent choice (polarity and composition)
- Type of paper used
- Sample size and concentration
- Temperature and humidity
- Time allowed for separation
11. How is paper chromatography different from thin layer chromatography (TLC)?
Paper chromatography uses cellulose paper as the stationary phase, while TLC uses a solid adsorbent layer (usually silica gel). TLC generally provides better separation, sharper spots, and can handle a wider range of mixtures compared to paper chromatography.
12. Why is it important to mark the solvent front immediately after removing the paper from the chamber?
Marking the solvent front immediately is crucial because the solvent evaporates quickly once the paper is removed. Accurate marking ensures precise calculation of Rf values for proper identification and analysis of components.
