Question Constellation Sign up for free AQA · GCSE · Chemistry · Higher
Chromatography solvent-front distance calculation
Figure 5 shows the results of Experiment 3 using orange dye B.
The student calculated that the Rf value of the orange dye in the experiment shown in Figure 5 was 0.48.
Calculate the distance moved by the solvent front when the orange dye had moved 5.4 cm.
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 Substitutes 0.48 and 5.4 cm into the Rf relationship correctly.
- 2 Rearranges to divide 5.4 by 0.48.
- 3 Gives 11.25 cm, or an accepted correctly rounded value.
Full-mark answer
Rf = distance moved by dye ÷ distance moved by solvent. Therefore distance moved by solvent = 5.4 ÷ 0.48 = 11.25 cm.
Why this answer loses marks
The student multiplies the dye distance by the Rf value.
Rf is dye distance divided by solvent distance, so the equation must be rearranged before finding the solvent distance.