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Rf Value - GCSE Chemistry Definition

Reviewed by: Richard Boole

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The Rf value is a number used in chromatography to show how far a substance travels compared to the solvent. It helps identify substances in a mixture.

It is calculated using the formula:

Rf = fraction numerator left parenthesis distance space moved space by space the space substance right parenthesis over denominator left parenthesis distance space moved space by space the space solvent right parenthesis end fraction

In paper chromatography, spots from a mixture are placed on chromatography paper. As the solvent rises, it carries the substances with it. Different substances move different distances, depending on their solubility and attraction to the paper.

Rf values are used to compare results and help identify unknown substances by matching them to known Rf values under the same conditions.

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Richard Boole

Reviewer: Richard Boole

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Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

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