Required Practical: Investigating Chromatography (AQA GCSE Chemistry): Revision Notes

Paper Chromatography is a technique used to separate and identify the different coloured chemicals that make up mixtures like black ink. In this practical, you'll use chromatography to see the different components in black ink.

Method:

1. Prepare the Chromatography Paper:

• Take a piece of chromatography paper and, using a ruler and pencil, draw a straight line across it, 2 cm from one of the short edges.
• Important: Use a pencil, not ink, as ink would dissolve in the solvent.

2. Prepare the Solvent:

• Pour a small amount of solvent into a beaker, making sure it's about 1 cm deep.

3. Apply the Ink:

• Using a pipette, place a drop of black ink onto the centre of the pencil line you drew earlier.
• Draw a circle around the ink drop using the pencil.

4. Set Up the Experiment:

• Carefully place the chromatography paper into the beaker so that the pencil line (and the ink spot) is just above the surface of the solvent. Make sure the ink spot doesn't touch the solvent.

5. Allow the Solvent to Move:

• Cover the beaker with a watch glass and allow the solvent to move up the chromatography paper.
• When the solvent front is about 1 cm from the top of the paper, carefully remove the paper from the beaker.

6. Mark the Solvent Front and Ink Spots:

• Use a pencil to draw a line across the paper where the solvent stopped moving (the solvent front).
• Circle any spots left by the separated ink on the paper.

Analysis 7. Measure the Distances:

• Use a ruler to measure the distance between the pencil line (where you started) and the solvent front.
• Measure the distance each ink spot has moved from the starting line. When doing this, measure from the centre of each spot.

8. Calculate the Rf Values:

• To calculate the Rf value for each spot, use this formula:

• Remember, the Rf value helps identify the different chemicals in the ink by showing how far each one moved up the paper compared to the solvent.