Understanding Paper Chromatography Techniques

Sep 17, 2024

Lecture Notes: Paper Chromatography

Introduction

  • Topic: Paper Chromatography
  • Purpose: Separate different substances in a mixture for identification.
  • Application: Example used - separating dyes in ink.

Chromatography Process

  • Materials Needed:
    • Filter paper
    • Pencil
    • Solvent (e.g., water or ethanol)
    • Beaker
    • Sample ink

Steps

  1. Prepare the Filter Paper:
    • Draw a baseline with pencil near the bottom.
    • Add sample of ink on the baseline.
  2. Prepare the Solvent:
    • Fill a beaker with a shallow amount of solvent.
  3. Place Paper in Solvent:
    • Ensure pencil line and ink spot are above the solvent.
    • Cover beaker to prevent solvent evaporation.
  4. Wait for Separation:
    • Solvent travels up paper, dyes dissolve and move at different rates.
  5. Finish:
    • Remove paper when solvent nears the top.
    • Dry paper to reveal chromatogram pattern.

Theory

  • Chromatogram: Pattern of spots indicating separation of substances.
  • Phases: Mobile and Stationary
    • Mobile Phase:
      • Substance in which molecules move.
      • Liquid or gas (solvent in paper chromatography).
    • Stationary Phase:
      • Substance in which molecules can't move.
      • Typically solid or thick liquid (filter paper).
    • Process:
      • Chemicals in ink alternate between mobile and stationary phases.
      • Solubility and attraction determine rate of movement.

Calculating Rf Values

  • Definition: Ratio of distance travelled by substance to distance travelled by solvent.
  • Formula:
    • ( Rf = \frac{\text{Distance travelled by substance}}{\text{Distance travelled by solvent}} )
  • Example:
    • If a substance travels 6 cm, solvent travels 10 cm, then ( Rf = 0.6 ).

Important Considerations

  • Pure Substances:
    • Yield a single spot on chromatogram with a specific Rf value.
  • Variable Factors:
    • Different solvents or paper types affect chromatogram and Rf values.
    • Chemists must consider these when comparing Rf values.

Conclusion

  • Appreciate the importance of solvent and paper type in chromatography.
  • Reiteration of chromatography’s utility in identifying chemicals.
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