AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2023: Question 3
10 marks · Low Demand difficulty · Short Answer
Label a paper chromatography setup, identify an experimental error, explain why a dye is a mixture, calculate an Rf value from measurements, and identify the spot with the greatest Rf value.
Practise this questionQuestion
Question text
03 This question is about chromatography.
A student investigated an orange dye using paper chromatography.
03.1 Figure 3 shows the apparatus at the start of the investigation.
Figure 3
Complete the labels on Figure 3.
[3 marks]
03.2 Figure 4 shows the results at the end of the investigation.
Figure 4
The student made a mistake in the investigation.
What mistake did the student make to produce the results shown in Figure 4?
[1 mark]
Tick ( ) one box.
Left the investigation for too long
Used a lid on the beaker
Used a solvent which did not dissolve the dye16
A different student did the investigation correctly.
Figure 5 shows the results.
Figure 5
03.3 How do the results in Figure 5 show that the orange dye is not a pure substance?
[1 mark]
03.4 Determine the Rf value for the red spot.
You should measure:
• the distance moved by the red spot
• the distance moved by the solvent.
Use Figure 5 and the equation:
distance moved by red spot
Rf =
distance moved by solvent
[4 marks]
Distance moved by red spot cm
Distance moved by solvent cm
Rf =
03.5 Which spot had the greatest Rf value?
Use Figure 5.
[1 mark]
Tick ( ) one box.
Dark yellow spot
Pale yellow spot
Red spot
Mark scheme
Show the mark scheme
AO /
Question Answers Mark
Spec. Ref.
03.1 AO1
4.8.1.3
RPA6
AO /
Question Answers Extra information Mark
Spec. Ref.
03.2 left the investigation for too long 1 AO3
4.8.1.3
RPA6
AO /
Spec. Ref.
03.3 (there is) more than one spot 1 AO3
or 4.8.1.1
(there are) three spots 4.8.1.3
– HEMISTRY – – RPA6
AO /
Spec. Ref.
03.4 (distance moved by red spot) = allow a value in the range 1.6 to 1 AO2
1.8 (cm) 2.0 (cm) 4.8.1.3
RPA6
(distance moved by solvent) = allow a value in the range 7.1 to 1
7.2 (cm) 7.3 (cm)
1.8 allow correct use of incorrectly 1
(Rf =)
7.2 determined distance(s)
= 0.25 1 11
AO /
Spec. Ref.
03.5 dark yellow spot 1 AO3
4.8.1.3
RPA6
– – 8462/2F –
Total Question 3 10
Question 4
How to answer it
AQA GCSE Chemistry: Paper Chromatography & Rf Values
This question focuses on Required Practical 6 (RPA 6) in Unit 8 (Chemical Analysis):
- Recalling and labelling the standard laboratory apparatus for paper chromatography.
- Troubleshooting practical errors in chromatography runs.
- Distinguishing between pure substances and mixtures using chromatogram spots.
- Measuring accurate distances with a ruler and calculating the retention factor (Rf).
- Interpreting comparative mobility of dyes to identify the substance with the highest Rf.
Labelling the Chromatography Apparatus
Identifying key components of the practical setup
✅ Correct Answers
- Top label: (Chromatography) paper
- Middle label: (Orange) dye (spot) or sample / ink
- Bottom label: Pencil line or start line / baseline
💡 Key Practical Rules
- Always use pencil: Pencil lead is insoluble graphite, so it won’t dissolve in the solvent or run up the paper.
- Solvent level: Must be below the pencil baseline so the sample spot doesn't dissolve directly into the solvent pool.
- Lid: Stops the solvent from evaporating before reaching the top.
Identifying Experimental Errors
Analysing why dye pooled at the very top of the strip
✅ Correct Answer
Left the investigation for too long (Tick box 1)
🧠 Examiner Insight
If the paper is left running too long, the solvent front reaches the top of the paper. All separated pigments catch up with each other at the solvent front and merge into a single band at the top edge.
❌ Common Misconception
Ticking "Used a solvent which did not dissolve the dye". If the dye were insoluble, it would stay on the baseline at the bottom and not move at all!
Interpreting Purity from a Chromatogram
Explaining evidence that the orange dye is a mixture
✅ Correct Answer
(There is) more than one spot
or (There are) three spots
💡 Pure Substance vs Mixture
- Pure substance: Produces only a single spot in any given solvent.
- Mixture / Formulation: Separates into two or more spots because different dyes have different attractions to the stationary and mobile phases.
Calculating the Rf Value of the Red Spot
Ruler measurements, formula substitution, and ratio calculation
📐 Step-by-Step Calculation
- Measure distance moved by red spot:
Measure from baseline to centre of red spot = 1.8 cm
(Allowed range: 1.6 to 2.0 cm) [1 mark] - Measure distance moved by solvent:
Measure from baseline to solvent front = 7.2 cm
(Allowed range: 7.1 to 7.3 cm) [1 mark] - Substitute into Rf formula:
Rf = 1.8 / 7.2 [1 mark] - Calculate final value:
Rf = 0.25 [1 mark]
❌ Critical Traps to Avoid
- Measuring from the paper bottom: Always measure from the pencil baseline, never from the very bottom of the paper.
- Measuring to the wrong part of the spot: Always measure to the vertical centre of the spot.
- Adding units: Rf is a ratio (cm ÷ cm), so it has no units.
- Rf greater than 1: A spot can never travel further than the solvent. If your answer is > 1, you divided upside down!
Comparing Rf Values
Determining which spot travelled the furthest
✅ Correct Answer
Dark yellow spot (Tick box 1)
🧠 Why is this?
The greatest Rf value belongs to the spot that moved the furthest distance from the baseline.
- Dark yellow spot: Travelled highest up the paper → highest Rf.
- Red spot: Travelled least distance → lowest Rf.
💡 Stationary vs Mobile Phase
The dark yellow pigment has a high Rf because it is more soluble in the mobile phase (solvent) and less strongly attracted to the stationary phase (paper).
Topics
Chemistry · Required Practicals · C8: Chemical Analysis · Required Practicals
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Foundation), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.