LA

(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.