Chromatography GCSE Chemistry Practical

Preparation and Setup

1. Gather Materials
• Collect all necessary equipment, including chromatography paper, pencil, capillary tubes, food dye samples, a wooden splint, a paperclip, and a 250ml beaker.
2. Prepare the Chromatography Paper
• Draw a pencil line 2cm from the bottom edge of the chromatography paper. This will serve as the baseline for your samples.
• Mark five small crosses along the pencil line, spaced evenly and at least 5mm from the edges. Label the crosses A, B, C, D, and X (for the unknown mixture).

Applying the Dyes

1. Spotting the Samples
• Dip the open end of a capillary tube into the first food dye sample to draw up a small amount of dye.
• Touch the open end of the capillary tube to the cross marked A to deposit a small spot of dye.
• Allow the spot to dry, then repeat to make the spot more concentrated.
• Use a fresh capillary tube for each dye sample and repeat the process for B, C, D, and the unknown mixture X.

Setting Up the Experiment

1. Prepare the Chromatography Strip
• Wrap the top end of the chromatography paper around a wooden splint and secure it with a paperclip.
• Add 1cm of water to a 250ml beaker. Ensure the depth of the water does not touch the pencil baseline when the paper is placed inside.
2. Begin the Chromatography
• Once the spots are dry, carefully lower the chromatography paper into the beaker. The pencil baseline should stay above the water surface, and the paper should not touch the sides of the beaker.
• Rest the wooden splint across the top of the beaker to hold the paper in place.

Observations and Results

1. Monitor the Process
• Observe as the water travels up the paper, carrying the food dyes. Watch for the dye mixture X to begin separating into its components.
• Remove the paper when the water is near the top and mark the highest point reached by the solvent with a pencil line. Allow the paper to dry completely.
2. Record Measurements
• Measure the distance in millimetres from the baseline to the solvent front (the top pencil line). This is the distance moved by the solvent.
• For each food dye spot, mark the centre of the spot with a pencil and measure the distance from the baseline to the spot centre. Record all measurements in a table.

Calculations and Analysis

1. Calculate Rf Values
• Use the formula: Rf=Distance moved by dye spotDistance moved by solventR_f = \frac{\text{Distance moved by dye spot}}{\text{Distance moved by solvent}}Rf​=Distance moved by solventDistance moved by dye spot​
• Calculate the Rf value for each dye spot and record these in the table.
2. Identify Components
• Compare the Rf values of the dye mixture X with the known dyes A, B, C, D to identify the individual components present in the mixture.