All calculations
Chromatography Rf
Chemical analysis
AQA 8462
ORIGINAL
Rf = distance moved by substance / distance moved by solvent
Both distances start at the pencil baseline, and the solvent front always goes underneath the fraction.
Verified against AQA 8462 (2026 spec)
Work it, then mark it
Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.
Q1
2 marks
A dye spot moves 5.4 cm from the baseline while the solvent front moves 7.2 cm. Calculate Rf.
Do the calculation on paper first — then mark it.
Where the marks get lost
- Measuring from the bottom of the paper instead of the baseline.
- Giving Rf a unit or obtaining a value above 1.
Exam tip: Rf has no unit and must lie between 0 and 1 for a spot that remains below the solvent front.
Calculations are the most trainable marks in chemistry
They come up every paper and reward a clean method. Send me one you keep dropping marks on — your first lesson is free.