Edexcel IGCSE Chemistry 1.12 Rf values
Practise measuring chromatogram distances, calculating Rf values and using them to identify dyes in mixtures.
- Syllabus
- First assessment 2019
- Course
- Chemistry 4CH1
Exam points
- calculate Rf from spot distance divided by solvent-front distance, with correct rounding
- use an Rf value and a chromatogram scale to identify the matching dye or food colouring
- reject impossible Rf values greater than 1 using the solvent-front position
1.12 Rf values question 1
[Maximum number: 3]
A student uses paper chromatography to investigate the dyes in five different inks, V, W, X, Y and Z.
This is what she uses.
- a beaker
- a piece of chromatography paper with a pencil line drawn near the bottom of the paper
- a solvent
- inks V, W, X, Y and Z
One dye in ink Y moves 4.3 cm when the solvent front moves 6.5 cm.
Calculate the Rf value for this dye.
Give your answer to 2 significant figures.
Rf value = ................................
- Rf = 4.3 / 6.5
- 0.6615
- 0.66
Accept:
- any number of significant figures for the intermediate value
Marking guidance:
- Correct equation for finding Rf scores 1 mark.
- Final answer must be 2 significant figures.
- 0.66 with no working scores 3.
- Correct answer to 3 or more significant figures with no working scores 2.
- Final-answer mark subsumes the intermediate-value mark.
- ECF can score the calculation and final-answer marks if 4.3 and 6.5 are used in a division.
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