Required Practical 6

Aim

To investigate how paper chromatographyThe separation of compounds using a stationary and mobile phase. can be used to separate and tell the difference between coloured substances.

Materials Needed

• Chromatography paper or filter paper strip
• Coloured markers or water-soluble ink pens of different colours (at least three)
• Pencil or pen
• Beaker or glass
• Ruler
• Solvent (e.g., water or rubbing alcohol)
• Clothespin or paperclip
• Safety goggles and lab coat

Safety Precautions

• Wear safety goggles and a lab coat to protect against accidental splashes.
• Do not ingest or touch any chemicals or solvents, and handle all materials with care.

Procedure

1. Preparation of the Chromatography Paper:
   1. Draw a horizontal line using a pencil or pen about 1 cm from the bottom edge of the chromatography paper.
   2. On the line, place small dots of different coloured markers or ink pens, each spaced a few centimetres apart.
2. Development of the Chromatogram:
   1. Fill a beaker or glass with a small amount of the chosen solvent (enough to immerse the bottom part of the chromatography paper).
   2. Attach the chromatography paper to a pencil or clothespin, ensuring that the bottom of the paper is immersed in the solvent without touching the sides of the beaker.
   3. Allow the solvent to travel up the paper by capillary action until it approaches the top edge of the paper.
3. Calculation of Rf Values:
   1. Measure the distance travelled by each coloured substance from the baseline to the centre of the spot (distance moved by the substance).
   2. Measure the distance travelled by the solvent from the baseline to the centre of the solvent front (distance moved by the solvent).
   3. Calculate the Rf value for each coloured substance using the formula: Rf = (Distance moved by the substance) / (Distance moved by the solvent).
4. Interpretation of Results:
   1. Observe the separated colours on the chromatography paper and note any differences in their positions and distances travelled.
   2. Compare the Rf values obtained for each coloured substance.
   3. Discuss how the Rf values help in identifying and distinguishing between different coloured substances.
5. Conclusion:
   1. Summarise the findings of the investigation, stating how paper chromatography can be used to separate and differentiate between coloured substances.
   2. Discuss the significance of Rf values in identifying substances in a mixture.
   3. Reflect on any potential sources of error and suggest improvements for future experiments.