GCSE & IGCSE chemistry practice

Rf values questions and answers

In paper chromatography, each substance's Rf value is: $R_f = \dfrac{\text{distance moved by substance}}{\text{distance moved by solvent}}$ . Both distances are measured from the start (pencil) line. An Rf value is always between 0 and 1, and it identifies a substance in a given solvent.

15 questions · Foundation tier · Every answer is checked as you type it, with a full worked solution. Updated 10 Nov 2026.

Start the questions Chromatography guide Rf value calculator

Where rf values comes up

GCSE (AQA)	Chemistry and Combined Science, Foundation and Higher: interpret chromatograms and determine Rf values. Chromatography is a required practical.
Cambridge IGCSE (0620)	Core: interpret simple chromatograms to identify substances and to tell pure from impure. Supplement (Extended): state and use the equation for Rf.

The method

Measure from the start line to the centre of the spot, and from the start line to the solvent front.
Rf = spot distance ÷ solvent distance.
Same Rf in the same solvent: probably the same substance.
One spot: pure. More than one: a mixture.

Rf values questions

Try each one before looking at the hint. If you're stuck, the AI tutor can talk you through it step by step.

Warm-up

Question 1Warm-upFoundation

A spot moves 3 cm and the solvent moves 6 cm. Calculate the Rf value.

Question 2Warm-upFoundation

A spot moves 2.4 cm and the solvent front moves 8.0 cm. Calculate the Rf value.

Question 9Warm-upFoundation

A spot moves 5.6 cm and the solvent front moves 8.0 cm. Calculate the Rf value.

Question 10Warm-upFoundation

A spot moves 1.5 cm and the solvent front moves 6.0 cm. Calculate the Rf value.

Exam-style

Question 3Exam-styleFoundation

The solvent moves 10 cm. A substance has an Rf value of 0.45. How far does it move?

Question 4Exam-styleFoundation

A dye has an Rf of 0.6 and moved 4.2 cm. How far did the solvent move?

Question 5Exam-styleFoundation

An ink gives three spots. How many substances does it contain at least, and is it pure?

Question 6Exam-styleFoundation

An unknown dye has Rf 0.35. Known dyes in the same solvent: A 0.20, B 0.35, C 0.62. Which is the unknown?

Question 11Exam-styleFoundation

The solvent front moves 12 cm. A substance has an Rf value of 0.75. How far does it move?

Question 12Exam-styleFoundation

A dye has an Rf value of 0.55 and moved 3.3 cm. How far did the solvent move?

Question 13Exam-styleFoundation

Why is the start line on chromatography paper drawn in pencil, not pen?

Challenge

Question 7ChallengeFoundation

A student calculates an Rf of 1.25. What has gone wrong?

Question 8ChallengeFoundation

Two spots on the same chromatogram move 1.8 cm and 5.4 cm. The solvent moves 9.0 cm. What is the difference between their Rf values?

Question 14ChallengeFoundation

A spot's centre is 3.6 cm above the start line. The solvent front is 12.0 cm above the start line, which is 1.5 cm from the bottom of the paper. Calculate the Rf value.

Question 15ChallengeFoundation

Two substances have Rf values of 0.25 and 0.65. The solvent front moves 8.0 cm. How far apart are the two spots?

Common mistakes

Dividing the solvent distance by the spot distance (Rf must be less than 1).
Measuring from the bottom of the paper.
Drawing the start line in ink (it would run).

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Sources

The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:

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