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Specimen lab book: Chromatography
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Study Hack Lab
RP 6 · Chemistry
Chromatography
Lab book
Name
Specimen
Date
2 November 2026
Course
GCSE Chemistry
Board and specification
AQA GCSE Chemistry (8462), 4.8.1.3AQA GCSE Combined Science: Trilogy (8464), 5.8.1.3Apparatus and techniques: AT 1, AT 4
Run
C29HO
Status
Finished: every stage done
Exam questions
30/30 marks
Aim
Separate four food colourings (A–D) and an unknown mixture (U) by paper chromatography, calculate Rf values and find out which colourings are in U.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
Exam questions on your data
Simulated data produced by Study Hack Lab from the student's own run (seed 20261004). Every reading, value and mark here is from that run; nothing has been retyped. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
The solvent (the mobile phase) soaks up the paper (the stationary phase) and carries each dye with it. A dye that is more soluble in the solvent and less attracted to the paper spends more time moving, so it travels further. Each dye in a mixture moves its own fraction of the solvent’s distance, its Rf value, so the mixture separates.
Rf = distance moved by substance ÷ distance moved by solvent
Variables
Independent (you change)
The colouring (A, B, C, D or U)
Dependent (you measure)
Distance moved by each spot in mm
Control (you keep the same)
The paper and the solvent; Depth of solvent and height of the start line; Size of the spots; Temperature
Prediction
U is a mixture of colourings. What do you expect its spot to do as the solvent rises?
Split into separate spots, one for each colouring in it.Right first time
U split into 3 spots. Each dye in a mixture is attracted to the paper and dissolves in the solvent by different amounts, so each one moves its own distance and they separate.
Dye X is very soluble in the solvent and only weakly attracted to the paper. Compared with other dyes, X will…
Move further up the paper (a bigger Rf).Right first time
A dye spends its time either dissolved in the moving solvent (mobile phase) or stuck to the paper (stationary phase). More soluble and less attracted to the paper means more time moving.
How many spots will a pure substance give?
One spot, in any solvent.Right first time
A pure substance contains only one compound, so there is nothing to separate: it gives one spot whatever the solvent (only its Rf changes). Each of A–D gave one spot of its own colour.
Risk assessment
Hazard
Harm it could cause
Control you chose
Capillary tubes break easily
Cuts to the fingers from sharp glass
Handle them gently, do not use chipped ones and put broken glass in the broken-glass bin.Right first time
Ethanol (if used as the solvent) is highly flammable
It could catch fire and cause burns
No flames in the room; use a small volume and keep the lid on the beaker.Right first time
Food colourings and solvent splashed in the eyes
Sore, irritated eyes
Wear safety goggles throughout.Right first time
Spilt solvent on the floor
Slips and falls
Wipe up spills straight away.Right first time
2 Apparatus
✓Chromatography paper, cut to fit the beaker The stationary phase the dyes move along.
✓Pencil Draws the start line and the solvent front: graphite does not dissolve.
✓30 cm ruler (resolution 1 mm) Draws the start line and measures each distance.
✓Glass capillary tubes Put small, concentrated spots on the start line.
✓Food colourings A, B, C, D and the unknown U The samples to separate.
✓250 cm³ beaker Holds the solvent and the hanging paper.
✓Glass rod and tape The paper hangs from it across the top of the beaker.
✓Solvent: water (or ethanol and water) The mobile phase that carries the dyes up the paper.
✓Watch glass A lid, so the solvent does not evaporate from the paper.
✓White tile A clean, flat surface to spot and measure the paper on.
✓Safety goggles Protect your eyes from splashes and glass.
3 Method: your choices
Which version are you doing?: AQA required practical 6: food colouringsSeparate four food colourings and an unknown mixture, then find which colourings are in it.
Check the paper hangs clear of the beaker: DoneWhere the paper touches the glass, the solvent creeps up the wall faster and the front bends.
Put on safety gogglesSafety: DoneFood colourings, inks and solvent can splash into your eyes, and capillary tubes can break.
Draw the start line: In pencilGraphite does not dissolve in the solvent, so the line stays sharp and adds no colour.
Spot the colourings: Small spots: touch, let it dry, touch again (no more than 5 mm)Small, concentrated spots stay compact, so the colours in U pull apart cleanly and the centre of each spot is easy to find.
Choose the solvent: WaterAQA’s method. Each colouring has its usual Rf value in water.
Pour the solvent into the beaker: No more than 1 cm deep: below the start lineThe solvent soaks up the paper and carries the dyes up with it.
Get a lid ready: DoneA lid keeps the air in the beaker full of solvent vapour, so the solvent does not evaporate from the paper as it rises.
Choose how long to leave it: Until the solvent is about 1 cm from the topThe solvent moves 5–6 cm: the spots are well spread out and 1 mm is under 2 % of each distance.
Mark the solvent front straight away: DoneThe wet edge fades within a minute as the solvent evaporates; the solvent distance is measured to this line.
4 Results
12 of 12 readings taken.
Observations
Looking at
Observation
As the solvent rose
U splits into separate coloured spots
The start line
A sharp grey line, still in place
Lane U
3 spotsr
Lanes A to D
One spot each
Distances on the chromatogram · Every distance from the pencil start line: to the solvent front, and to the centre of each spot.
Spot
Distance moved by solvent in mm
Distance moved by spot in mm
Rf value
A
56
11
0.20
B
56
49
0.88
C
56
18
0.32
D
56
31
0.55
U, top
56
24
0.43
U, middle
56
17
0.30
U, bottom
56
11
0.20
r Recorded for you by the app.
Anomaly: No anomalous reading.
5 Graph
This practical has no graph: the results are in the table above.
6 Analysis
Rf values
A 0.20 · B 0.88 · C 0.32 · D 0.55 · U1 0.43 · U2 0.30 · U3 0.20Right first time
What is in U?
A, C and one other colouringRight first time
Pure or a mixture?
Which of your samples could be pure substances?
A, B, C and D: each gives a single spotRight first time
7 Conclusion and evaluation
Quantity
Your value
Accepted value
Rf of A (dark blue) in water
0.20
0.19
Rf of B (blue) in water
0.88
0.88
Rf of C (crimson) in water
0.32
0.32
Rf of D (red) in water
0.55
0.56
Conclusion
From your chromatogram, which colourings are in U?
A and C, and one colouring that is not A, B, C or DRight first time
U contains A and C (a spot of the same colour at the same Rf as each) and a third colouring that matches none of A–D.
Sources of error
Finding the centre of each spot (spots spread out as they move): systematic or random?
RandomRight first time
Each spot distance can be a millimetre or two out either way, more for big smeared spots, so Rf values scatter.
Solvent front marked after it had dried: systematic or random?
SystematicRight first time
Once dry, the front cannot be seen, so the line is a guess. Every Rf on that paper is out in the same direction: too big if the line is below the real front (solvent distance too small), too small if it is above.
Start line drawn in ink: systematic or random?
SystematicRight first time
The ink dissolves and runs up every lane, adding a coloured patch that is not in any sample.
Solvent above the start line: systematic or random?
SystematicRight first time
The colourings dissolve into the solvent in the beaker, so every spot is faint and a faint dye may not show.
Paper touching the beaker wall: systematic or random?
SystematicRight first time
The solvent front bends up on that side, so spots there move further and their Rf values are too high.
Ruler resolution (1 mm) on short distances: systematic or random?
RandomRight first time
Each distance is only to the nearest millimetre, so each Rf can be a few hundredths out, more when the solvent has not moved far.
Solvent evaporating from the paper (no lid): systematic or random?
RandomRight first time
The front rises unevenly, so Rf values vary from lane to lane.
Improvement
Which change would most improve your results?
Use small, concentrated spots (touch, dry, touch again) so they stay compact.Right first time
Repeatable or reproducible
You run a second chromatogram of the same colourings, the same way with the same equipment, and get almost the same Rf values. This shows your results are…
RepeatableRight first time
Repeatable: the same person, method and equipment give similar results.
Another group, using different paper from a different box, gets similar Rf values for the same colourings. This shows the results are…
ReproducibleRight first time
Reproducible: a different person, or different equipment, gives similar results.
8 Make safe and clear up
Pour the solvent away: water down the sink, ethanol into the residue bottle
Put used and broken capillary tubes in the broken-glass bin
Let the chromatogram dry completely, then keep it flat for your results
Wipe the bench, wash your hands, then take your goggles off
9 Exam questions on your data
On your own readings, self-marked against the mark scheme, with error carried forward where it applies. Total 30/30.
01.1[2 marks]
Explain why the start line on chromatography paper is drawn in pencil and not in ink.
Your answer
Ink would dissolve in the solvent and run up the paper with the dyes. Pencil is graphite, which is insoluble, so the line does not move.
2/2 self-marked
Ink would dissolve (in the solvent) and run up the paper / mix with the spots
Pencil (graphite) is insoluble / does not dissolve (so the line does not move)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: Ink would dissolve in the solvent and run up the paper, giving extra colours. Pencil (graphite) is insoluble, so the line does not move.
01.2[2 marks]
Figure 1 shows how a student set up a chromatography experiment.
Figure 1
Give two mistakes the student made in setting up the experiment.
Your answer
The start line is drawn in ink instead of pencil. The start line is below the water level, so the spots will dissolve into the water.
2/2 self-marked
The start line is drawn in ink / pen (allow it should be drawn in pencil)
The start line is below the water level (allow it should be above the water)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The start line is drawn in ink (it should be in pencil). The start line is below the water level (it should be above it).
01.3[1 mark]
A student uses chromatography to compare four food colourings on the same piece of paper.
Give one control variable in this investigation.
Your answer
The same solvent
1/1 self-marked
Any one of: type of paper; solvent; depth / volume of solvent; height of the start line; size of the spots; temperature
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The solvent (or: the paper, the depth of solvent, the size of the spots, the temperature).
01.4[1 mark]
Another student uses ethanol as the solvent instead of water.
Describe the hazard of using ethanol and the harm it could cause.
Your answer
Ethanol is flammable so it could catch fire and cause burns.
1/1 self-marked
Ethanol is (highly) flammable, so it could catch fire / cause burns
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: Ethanol is highly flammable, so it could catch fire and cause burns.
01.5[1 mark]
A student measured the distance moved by a spot with a 30 cm ruler marked in millimetres. They recorded it as 41.25 mm.
Explain why the distance should not be recorded to 2 decimal places.
Your answer
The resolution of the ruler is 1 mm so it cannot be used to measure to 2 decimal places.
1/1 self-marked
The resolution of the ruler is 1 mm, so it cannot measure to 2 decimal places
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The resolution of the ruler is 1 mm, so it cannot measure to 2 decimal places.
01.6[6 marks]
A student wants to find the Rf value of a food colouring using paper chromatography.
Describe a method the student could use to find the Rf value of the food colouring.
Your answer
1. Draw a start line in pencil about 2 cm from the bottom of the chromatography paper.
2. Use a capillary tube to put a small spot of the food colouring on the start line.
3. Pour a suitable solvent such as water into a beaker, about 1 cm deep.
4. Hang the paper in the beaker so the bottom dips in the solvent but the start line is above the solvent level.
5. Put a lid on the beaker.
6. Wait for the solvent to travel up the paper until it is near the top.
7. Take the paper out and mark the solvent front in pencil, then dry the paper.
8. Measure the distance from the start line to the centre of the spot.
9. Measure the distance from the start line to the solvent front.
10. Rf = distance moved by the spot ÷ distance moved by the solvent.
6/6 self-marked
Draw a start line in pencil on the chromatography paper
Put a (small) spot of the food colouring on the start line
Put a suitable solvent (water) in a beaker and stand the paper in it
The solvent level is below the start line
Use a lid
Wait for the solvent to travel up the paper (until it is near the top)
Mark the solvent front
Dry the paper
Measure the distance between the start line and the centre of the spot
Measure the distance between the start line and the solvent front
Use the measurements to work out Rf = distance moved by the spot ÷ distance moved by the solvent
Self-marked: Level 3, 6 of 6 marks. You ticked 11 of 11 indicative points. This is your own judgement against the mark scheme.
Model answer: 1. Draw a start line in pencil about 2 cm from the bottom of the chromatography paper.
2. Use a capillary tube to put a small spot of the food colouring on the start line.
3. Pour a suitable solvent such as water into a beaker, about 1 cm deep.
4. Hang the paper in the beaker so the bottom dips in the solvent but the start line is above the solvent level.
5. Put a lid on the beaker.
6. Wait for the solvent to travel up the paper until it is near the top.
7. Take the paper out and mark the solvent front in pencil, then dry the paper.
8. Measure the distance from the start line to the centre of the spot.
9. Measure the distance from the start line to the solvent front.
10. Rf = distance moved by the spot ÷ distance moved by the solvent.
02.1[3 marks]
On your chromatogram, the solvent moved 56 mm and the red spot in U moved 24 mm from the start line.
Calculate the Rf value of the red spot in U.
Give your answer to 2 significant figures.
Your answer
0.43
Working: Rf = 24 ÷ 56
Rf = 0.43
3/3
Rf = 24 ÷ 56
Rf = 0.429
Answer given to 2 significant figures: 0.43
Full marks. Your answer meets all the points for this question.
Model answer: Rf = 24 ÷ 56
Rf = 0.43
02.2[1 mark]
Another student’s solvent moved 58 mm. Table 1 shows their results.
Which result is anomalous?
Select one row.
Table 1
Colouring
Distance moved by spot in mm
Rf value
A
11
0.19
B
71
1.22
C
19
0.33
D
33
0.57
Your answer
colouring B
1/1
Colouring B: its Rf is more than 1, which is impossible
Full marks. That is exactly what the mark scheme is looking for. Colouring B has an Rf of 1.22: no substance moves further than the solvent, so it is a measuring mistake (for example, measuring from the bottom edge of the paper instead of the start line).
Model answer: Colouring B. Its Rf value is more than 1, but a substance cannot move further than the solvent.
02.3[3 marks]
Figure 2 and Table 2 show your chromatogram of colourings A, B, C, D and the unknown U.
Figure 2
Table 2
Colouring
Colour of spot(s)
Rf value(s)
A
dark blue
0.20
B
blue
0.88
C
crimson
0.32
D
red
0.55
U
red, crimson, dark blue
0.43, 0.30, 0.20
Which substances does U contain?
Tick (✓) three boxes.
✓ Colouring A (your choice)
Colouring B
✓ Colouring C (your choice)
Colouring D
✓ A colouring that is not A, B, C or D (your choice)
Nothing else: U is a pure substance
Your answer
Colouring A; Colouring C; A colouring that is not A, B, C or D
3/3
Colouring A
Colouring C
A colouring that is not A, B, C or D
Full marks. Well done.
Model answer: Colouring A and colouring C (same colours and Rf values as spots in U), and a colouring that is not A, B, C or D (U’s red spot matches none of them).
02.4[2 marks]
Use Figure 2 and Table 2. Compare colouring C with the unknown U.
Your answer
Colouring C could be a pure substance because it gives only one spot (a second solvent would test this). U is a mixture because it gives 3 spots.
2/2 self-marked
C could be a pure substance because it gives only one spot (one spot in one solvent does not prove it: a second solvent might separate it)
U is a mixture because it gives more than one spot (3)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: C could be a pure substance because it gives only one spot. U is a mixture because it gives 3 spots.
03.1[3 marks]
A dye has an Rf value of 0.56. On a chromatogram the dye moved 4.5 cm from the start line.
Calculate the distance moved by the solvent.
Give your answer to 3 significant figures.
Your answer
8.04
Working: 0.56 = 4.5 ÷ distance moved by solvent
distance = 4.5 ÷ 0.56
distance = 8.04 cm
3/3
0.56 = 4.5 ÷ distance moved by solvent (or distance = 4.5 ÷ 0.56)
8.036 cm
Answer given to 3 significant figures: 8.04
Full marks. Your answer meets all the points for this question.
Model answer: 0.56 = 4.5 ÷ distance moved by solvent
distance = 4.5 ÷ 0.56
distance = 8.04 cm
03.2[2 marks]
In water, the crimson dye moves further up the paper than the dark blue dye.
Explain why the crimson dye moves further than the dark blue dye.
Your answer
The crimson dye is more soluble in water and is less attracted to the paper, so it spends more time in the mobile phase.
2/2 self-marked
The crimson dye is more soluble in the solvent (water / mobile phase) (allow converse)
The crimson dye is less attracted to the paper (stationary phase) (allow converse)
So it spends more time in the solvent / mobile phase
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The crimson dye is more soluble in water (the mobile phase) and less attracted to the paper (the stationary phase), so it spends more time moving with the solvent.
03.3[1 mark]
Two different dyes have the same Rf value in water, so they show as one spot.
Suggest how a student could separate the two dyes.
Your answer
Use a different solvent such as ethanol.
1/1 self-marked
Use a different solvent (allow use ethanol)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: Use a different solvent, for example ethanol.
03.4[2 marks]
Another student left the paper to dry before drawing the line at the solvent front. They guessed where the front had been, and drew their line below where the solvent had really reached.
Explain how this would affect the student’s Rf values.
Your answer
The front was marked too low, which makes the distance moved by the solvent too small. So the Rf values would be too big.
2/2 self-marked
The line is below the real front, so the solvent distance measured is too small
So the Rf values are too large
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: The line was drawn below the real front, so the solvent distance measured is too small. So every Rf value is too big.
Unseen data: the same skills, new apparatus
01[1 mark]
A separate illustrative chromatogram was measured correctly.
Distances from the start line
Measurement
Distance in mm
Centre of spot
43
Marked solvent front
82
Calculate the Rf ratio from these recorded distances. Give your answer to 2 decimal places. Rf has no unit.
Your answer
0.52
Working: 43 / 82
1/1
Correct spot-to-solvent ratio, rounded to 2 decimal places.
Full marks. Clear and precise.
Model answer: 43 ÷ 82 = 0.52. Both distances use the same unit, so it cancels.
02[2 marks]
A student wants to compare dyes on a new chromatogram.
Which two actions protect the validity of the measured distances? Tick (✓) two boxes.
✓ Mark the solvent front immediately after removing the paper, before the solvent evaporates. (your choice)
✓ Measure from the pencil start line to the centre of the spot and to the marked solvent front. (your choice)
Measure from the bottom edge of the paper to make the distances larger.
Wait until the solvent has evaporated before deciding where the solvent front was.
Your answer
Mark the solvent front immediately after removing the paper, before the solvent evaporates.; Measure from the pencil start line to the centre of the spot and to the marked solvent front.
2/2
Mark the solvent front immediately after removing the paper, before the solvent evaporates.
Measure from the pencil start line to the centre of the spot and to the marked solvent front.
Full marks. Well done.
Model answer: Mark the front while it is visible, then use the same pencil origin for both distances. Evaporation can obscure the front; the paper edge is not the origin.
03[2 marks]
Unknown X and reference Y each form one visible spot of the same colour and Rf in the same solvent on the same paper.
Which two statements are justified? Tick (✓) two boxes.
✓ The observations support the suggestion that X contains Y, but do not prove identity. (your choice)
✓ Compare X and Y again using a suitable different solvent to look for further separation. (your choice)
One visible spot in one solvent proves X contains only one substance.
The Rf of X must be identical in every solvent and on every paper.
Your answer
The observations support the suggestion that X contains Y, but do not prove identity.; Compare X and Y again using a suitable different solvent to look for further separation.
2/2
The observations support the suggestion that X contains Y, but do not prove identity.
Compare X and Y again using a suitable different solvent to look for further separation.
Full marks. Well done.
Model answer: Matching colour and Rf under the same conditions support an identification. A different solvent can separate substances that travelled together; one spot in one solvent is not proof of purity.