(40) GCSE Chemistry Revision "Paper Chromatography"

Introduction to Paper Chromatography

• Paper chromatography is a separation technique used to separate substances in a mixture.

• It is a physical process, meaning it does not involve chemical reactions or the creation of new substances.

Separation Techniques Overview

• Other separation techniques previously discussed include:

  • Filtration

  • Crystallization

  • Simple distillation

  • Fractional distillation

• Chromatography is another method utilized by scientists for the separation of mixtures.

Principles of Paper Chromatography

• Paper chromatography separates substances based on their different solubilities.

Example of Paper Chromatography Process

1. Materials Needed:

   • Special chromatography paper

   • Colored pens (to demonstrate the separation of colors)

   • Solvent (liquid that dissolves substances)

2. Procedure:

   • Draw a pencil line near the bottom of the chromatography paper.

   • Place dots of different colors on the pencil line.

   • Immerse the bottom of the paper in a solvent.

3. Key Terminology:

   • Stationary Phase: The paper, which does not move.

   • Mobile Phase: The solvent, which moves and carries substances with it.

Observations After Solvent Movement

• After some time:

  • A pure color (e.g., red) will form a single spot on the paper, indicating it is a single pure substance.

  • A mixed color (e.g., color B) will separate into two or more spots, indicating it contains multiple substances.

Solvent Variability

• The same experiment can yield varying results with different solvents:

  • A pure compound will always produce a single spot regardless of the solvent used.

  • Mixtures may separate into different spots depending on the solvent.

Key Concepts in Chromatography

• Different substances have different solubilities.

• A more soluble substance is more attracted to the mobile phase (solvent) and will travel further up the paper.

Importance of Starting Line

• It is crucial to draw the starting line in pencil rather than pen:

  • Pen ink may dissolve in the solvent and contaminate the results.

Future Applications

• The concept of paper chromatography will be revisited in later topics, particularly in chemical analysis.

• It will be used to identify compounds by calculating the RF value (retention factor).

Additional Resources

• A revision workbook related to chromatography concepts and questions is available for further study.