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 in simple terms?
Paper chromatography is a technique used to separate different parts of a mixture, like the various colours in a pen's ink. It works by using a special paper where a solvent moves up, carrying the mixture's components at different speeds and causing them to separate into distinct spots.
2. What is the main principle behind how paper chromatography works?
The core principle is partition chromatography. This means substances in a mixture separate based on how they distribute (or partition) themselves between two phases:
- The stationary phase (the paper, which holds water molecules).
- The mobile phase (the solvent that moves up the paper).
3. What are the stationary and mobile phases in paper chromatography?
In paper chromatography, the two phases are:
- Stationary Phase: This is the chromatography paper itself, which is typically made of cellulose. The water molecules trapped within the pores of this paper act as the stationary liquid.
- Mobile Phase: This is the liquid solvent (like water, alcohol, or a mixture) that moves up the paper through capillary action, carrying the sample with it.
4. What does the Rf value tell us and how is it calculated?
The Rf (Retardation factor) value helps identify a compound. It is a ratio that measures how far a substance has moved compared to how far the solvent has moved. The formula is:
Rf = Distance travelled by the substance / Distance travelled by the solvent front.
Each compound has a unique Rf value under specific conditions, and it is always less than 1.
5. Why is selecting the right solvent so important for a successful experiment?
Choosing the right solvent is crucial because its polarity and composition directly control the separation. If the solvent is too polar, it might carry all components to the top without separating them. If it's not polar enough, the components might not move from the baseline at all. The ideal solvent moves the different components at noticeably different rates, resulting in a clear separation.
6. What are some real-world applications of paper chromatography?
Paper chromatography is used in many fields for analysis. Some common applications include:
- Separating the different pigments in plant leaves.
- Identifying substances in forensic science, like drugs or ink from a note.
- Checking for adulteration in foods and beverages.
- In the pharmaceutical industry, to check the purity of drugs.
7. How is paper chromatography different from Thin Layer Chromatography (TLC)?
While both are used for separation, they have key differences. Paper chromatography uses cellulose paper as the stationary phase. In contrast, TLC uses a thin layer of an adsorbent material like silica gel or alumina coated on a glass plate. Generally, TLC provides faster runs, better separation, and sharper spots than paper chromatography.
8. How can you see the separated spots if the compounds are colourless?
For colourless compounds, a locating agent or visualisation method is used after the chromatogram is developed. Common methods include:
- Spraying the paper with a chemical (like ninhydrin for amino acids) that reacts with the spots to produce a colour.
- Placing the paper under a UV lamp, which can make certain spots fluoresce and become visible.
9. What would happen if the starting line with the sample spot was accidentally dipped into the solvent?
If the starting line is below the solvent level, the experiment will fail. Instead of the solvent moving up the paper and separating the sample, the sample spot would dissolve directly into the solvent pool at the bottom of the container. No separation would occur on the paper.
10. Besides the solvent, what other factors can affect the separation of components?
Several factors can influence the final result:
- The quality of the paper: Different papers have different thicknesses and pore sizes.
- Temperature: Changes in temperature can alter solvent viscosity and the solubility of components.
- Purity of the solvent: Contaminants in the solvent can interfere with the separation.
- Chamber saturation: An atmosphere saturated with solvent vapour ensures the solvent moves up the paper evenly.
