AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2025: Question 5
12 marks · Standard Demand difficulty · Short Answer
Describe and analyze a paper chromatography experiment to separate ink dyes, including setup diagrams, Rf calculations, experimental variables, and comparison to gas chromatography.
Practise this questionQuestion
Question text
05 This question is about chromatography.
Figure 4 shows some equipment used for paper chromatography.
Figure 4
05.1 Complete Figure 4 to show how the equipment can be used to separate the dyes in
an ink.
You should draw and label:
• a piece of chromatography paper in the beaker
• a start line on the chromatography paper
• a spot of the ink on the chromatography paper at the start of the experiment.
[3 marks]
05.2 Why should a pencil be used to draw the start line on the chromatography paper?
[1 mark]
The Rf value of a dye was 0.80
A spot of the dye moved a distance of 5.2 cm.
05.3 Calculate the distance moved by the solvent.
*16Use the equation:*
distance moved by spot
Rf =
distance moved by solvent
[3 marks]
Distance moved by solvent = cm
05.4 How is the distance moved by the spot of the dye measured?
[1 mark]
Tick ( ) one box.
From the start line to the bottom of the spot
From the start line to the centre of the spot
From the start line to the top of the spot18
05.5 Which two changes could produce a different Rf value for this dye?
[2 marks]
Tick ( ) two boxes.
Use a different beaker.
Use a different length of time.
Use a different sized spot of dye.
*17Use a different solvent.*
Use a different type of chromatography paper.
05.6 A different dye is a pure substance.
How many spots will this dye produce during chromatography?
[1 mark]
05.7 Which is an advantage of using gas chromatography instead of
paper chromatography?
Choose the answer from the box.
[1 mark]
less sensitive more accurate slower
Gas chromatography is .
Mark scheme
Show the mark scheme
Question 5
AO /
Question Answers Extra information Mark
Spec. Ref.
05.1 labelled paper in solvent allow paper touching solvent 1 AO1
4.8.1.3
RPA6
labelled start line above solvent do not accept start line touching 1
level solvent
labelled ink spot on start line 1
if no other mark awarded allow 1
mark for a complete unlabelled
diagram
AO /
Spec. Ref.
05.2 (so the start line) does not allow (because an ink line) 1 AO1
smudge / run / dissolve would smudge / run / dissolve 4.8.1.3
or RPA6
pencil is insoluble
AO /
Spec. Ref.
05.3 5.2 1 AO2
0.80 =
distance moved by solvent 4.8.1.3
RPA6
5.2 1
distance moved by solvent =
0.80
= 6.5 (cm) 1
AO /
Spec. Ref.
05.4 from the start line to the centre 1 AO1
of the spot 4.8.1.3
RPA6
AO /
Spec. Ref.
05.5 use a different solvent 1 AO1
4.8.1.3
RPA6
use a different type of 1
chromatography paper
AO /
Spec. Ref.
05.6 1 1 AO2
4.8.1.1
4.8.1.3
AO /
Spec. Ref.
05.7 more accurate 1 AO2
4.8.3.6
Total Question 5 12
How to answer it
Paper Chromatography & Instrumental Analysis
What this question tests
This question assesses core knowledge from Required Practical 6 (Chromatography) and analytical chemistry:
- Setting up chromatography equipment accurately (baseline position, solvent depth).
- Understanding experimental controls (why pencil is used).
- Rearranging the Rf formula to calculate unknown distances.
- Distinguishing pure vs impure substances by spot count.
- Factors that change Rf values (stationary vs mobile phases).
- Advantages of modern instrumental methods (gas chromatography).
Experimental Setup Diagram
Completing and labelling the chromatography apparatus in Figure 4
✅ Mark Scheme Requirements
- Mark 1: Chromatography paper drawn inside the beaker, dipping into the solvent (solvent touches the bottom edge of the paper). Labelled: chromatography paper.
- Mark 2: A horizontal line drawn above the solvent level. Labelled: start line.
- Mark 3: A spot of ink drawn on the start line. Labelled: ink spot.
❌ Common Errors
- Drawing the start line below or level with the solvent — this scores 0 for that mark because the ink dissolves directly into the solvent pool instead of travelling up the paper.
- Drawing the setup correctly but forgetting to write labels (all three must be labelled to access all 3 marks).
Draw a vertical rectangle representing paper hanging down into the beaker with its bottom edge submerged in the solvent. Draw a neat horizontal pencil line across the paper 1–2 cm above the liquid level. Place a single clear dot on this horizontal line. Use three straight label lines pointing to the paper, the line, and the dot with their respective names.
Choice of Baseline Material
Why a pencil must be used to draw the start line
✅ Correct Answer
Any one of the following:
- Pencil (graphite) is insoluble in the solvent.
- So the line does not run, smudge, or dissolve in the solvent.
- If pen ink were used, it would dissolve and travel up the paper, interfering with the results.
🧠 Exam Technique
Always focus on the property of the material: solubility. Stating simply that "pencil is clearer" or "pencil looks neater" will earn 0 marks.
Calculating Solvent Distance (Rf Rearrangement)
Given: Rf = 0.80, Spot distance = 5.2 cm
📐 Step-by-Step Calculation
- Recall & Substitute:
Formula: Rf = distance moved by spot / distance moved by solvent
Substitute values: 0.80 = 5.2 / distance moved by solvent
[1 mark awarded for correct substitution] - Rearrange algebraically:
Multiply both sides by distance and divide by 0.80:
distance moved by solvent = 5.2 / 0.80
[1 mark awarded for rearrangement] - Calculate the final answer:
5.2 / 0.80 = 6.5 cm
[1 mark awarded for final value]
🧠 Sanity Check Trap
Because the spot can never travel further than the solvent, Rf must always be ≤ 1.0. Therefore, the distance moved by the solvent must be greater than the distance moved by the spot (6.5 cm > 5.2 cm).
❌ Common Miscalculation
Many students mistakenly multiply: 5.2 × 0.80 = 4.16 cm . If your solvent distance is smaller than your spot distance, you rearranged the equation upside down!
Measuring Spot Distance
Standard measurement procedure for chromatography spots
✅ Correct Option
From the start line to the centre of the spot
💡 Why the Centre?
Ink spots spread out as they travel. Measuring to the centre (midpoint) of the spot provides the most accurate and consistent representative position of the dye molecules.
Factors Affecting Rf Values
Which two changes produce a different Rf value?
✅ Correct Answers (Tick 2)
- Use a different solvent (Mark 1)
- Use a different type of chromatography paper (Mark 2)
💡 The Chemistry Behind Rf
Rf depends strictly on the relative attraction (partitioning) of the substance between two phases:
- Mobile phase: the solvent. Changing it changes the solubility of the dye.
- Stationary phase: the paper. Changing it changes how strongly the dye adsorbs/sticks.
Changing the beaker size, running time, or spot size does not change the dye's inherent Rf ratio.
Purity in Chromatography
How many spots will a pure substance produce?
✅ Correct Answer
1 (one single spot)
💡 Key Rule for Pure Substances
A pure substance consists of only one single element or compound. Under chromatography, it will only ever produce one spot, regardless of the solvent used. A mixture/formulation will separate into two or more spots.
Instrumental Methods: Gas Chromatography
Advantage of gas chromatography over paper chromatography
✅ Correct Option
Gas chromatography is more accurate.
💡 Advantages of Instrumental Methods
Compared to manual bench methods like paper chromatography, instrumental methods (like GC and GC-MS) are:
- Faster (not slower!)
- More sensitive (can detect tiny trace amounts; not less sensitive!)
- More accurate and reliable
Topics
Chemistry · Required Practicals · C8: Chemical Analysis · Required Practicals
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Foundation), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.