Chemistry · 12.3 Chromatography · Paper 5/6 practical
Paper Chromatography. Separate it.
Spot a mixture on the baseline and let the solvent rise. Components that are more soluble (or less attracted to the paper) travel further. Measure how far each spot and the solvent move, then calculate Rf = distance moved by substance ÷ distance moved by solvent.
0620 Topic 12.3 — Chromatography
Rf = d(spot) / d(solvent)
Paper 5/6 — Practical
front 0.0 cm
Draw the baseline in pencil (insoluble) and keep the solvent below it so the spots don't dissolve away.
Sample
—
Reference dyes (pure) run alongside: blue Rf 0.30, red Rf 0.55, yellow Rf 0.80.
Measurements
Solvent front
0.0 cm
Spots resolved
0
Conclusion
run the chromatogram…
Rf table
Measure after the solvent has risen.
📋 Method (Cambridge practical procedure)
- Draw a baseline about 1 cm from the bottom of the paper in pencil.
- Put a small spot of each mixture (and reference dyes) on the baseline; let it dry.
- Stand the paper in a beaker with solvent below the baseline; cover to saturate with vapour.
- Let the solvent rise until near the top, then remove and immediately mark the solvent front in pencil.
- Measure the distance moved by each spot and by the solvent from the baseline.
- Calculate Rf = distance moved by spot ÷ distance moved by solvent (always < 1). Identify components by matching Rf to references.
- For colourless substances (e.g. amino acids), spray with a locating agent (e.g. ninhydrin) to show the spots.
⚠ Sources of error & precautions
- Baseline in pencil — pen ink would dissolve and run up the paper.
- Keep the solvent level below the baseline so the spots are not washed into the solvent.
- Measure to the centre of each spot.
- Cover the beaker so the atmosphere is saturated and the solvent rises evenly.
- The same substance always has the same Rf in a given solvent — use it to identify unknowns.
🎯 Syllabus reference (0620)
- 12.3 Chromatography — describe paper chromatography to separate soluble coloured (and, with a locating agent, colourless) substances; interpret chromatograms; state and use Rf = distance moved by substance ÷ distance moved by solvent.