Paper Chromatography for Identifying Substances

Introduction

• Paper chromatography is a separation technique used to identify substances based on their solubility.
• Other separation methods include filtration, crystallization, and distillation (simple and fractional).

Paper Chromatography Process

1. Materials Needed:

   • Chromatography paper
   • Pencil to draw a line
   • Colored pens or substances to test
   • Solvent (liquid that dissolves substances)

2. Steps:

   • Draw a pencil line near the bottom of the chromatography paper.
   • Place dots of various colors on the pencil line.
   • Immerse the bottom of the paper in a solvent.
   • The solvent moves up the paper, dissolving the ink in the color dots.

3. Phases:

   • Stationary Phase: The paper, which does not move.
   • Mobile Phase: The solvent, which moves up the paper.

Results and Analysis

• Pure Substances: Produce a single spot on the paper.
• Mixtures: Separate into multiple spots, indicating different components.
• Example: Red color formed a single spot (pure), while another color formed two spots (mixture).

Important Concepts

• Different substances have varying solubilities.
• A more soluble substance travels further up the paper.
• Starting line is drawn in pencil to prevent it from moving with the solvent.

Identifying Unknown Substances

1. Spotting Unknowns:

   • Place a dot of the unknown chemical on the pencil line.
   • Immerse it in a solvent and observe movement.
   • One spot indicates purity.

2. Calculating RF Value:

   • Measure the distance moved by the substance (e.g., 44 mm).
   • Measure distance moved by the solvent (e.g., 75 mm).
   • Calculate RF = (Distance moved by substance) / (Distance moved by solvent) = 0.57 (no units).

3. Using RF Value:

   • Compare RF value in a database to identify the substance.
   • Repeat with different solvents if necessary.
   • Additional analysis needed if no matching RF value is found.

Conclusion

• Paper chromatography is a practical method for identifying substances in a mixture.
• RF values are key in identifying unknown substances.
• Further testing and database comparison are often necessary.

• For more practice, refer to additional questions in the revision workbook.