AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2024: Question 3

9 marks · Standard Demand difficulty · Short Answer

Identify formulation as a designed mixture and use paper chromatography to explain the start line choice, calculate an Rf value, and identify a blue dye in printer ink from Rf data.

Practise this question

Question

The question page is headed with Question 03 and states that printer ink is a mixture of chemicals. Part 03.1 asks for the name given to a mixture designed as a useful product, with tick-box options formula, formulation, and fraction. A chromatogram diagram labelled Figure 2 shows a rectangular strip with a start line near the bottom, a solvent front near the top, and two spots above the start line: a lower grey spot labelled red and a higher black spot labelled blue. Later parts ask what should be used to draw the start line and why, then ask students to calculate the Rf value of the red colour using the formula Rf equals distance moved by colour divided by distance moved by solvent, and finally use a table of blue colours with Rf values—Cerulean 0.40, Cobalt 0.15, Prussian 0.88, Ultramarine 0.68—to identify which blue dye matches a measured value of 0.86.
Question text

03 Printer ink is a mixture of chemicals.

03.1 What is the name given to a mixture that has been designed as a useful product?

[1 mark]

Tick ( ) one box.

Formula

Formulation

Fraction

A student used chromatography to investigate the colours in a printer ink.

Figure 2 shows the chromatogram.

Figure 2

03.2 The student used a ruler for the start line.

What would the student have used to draw the start line?

*10* Give one reason for your answer.

[2 marks]

Reason

03.3 Determine the Rf value of the red colour.

Use the equation:

distance moved by colour

Rf =

distance moved by solvent

[4 marks]

Distance moved by red colour

Distance moved by solvent

Rf =

03.4 Table 2 shows the Rf values of four blue colours.

Table 2

Blue colour Rf

Cerulean 0.40

Cobalt 0.15

Prussian 0.88

Ultramarine 0.68

The student determined that the Rf value of the blue colour in the printer ink was 0.86

Suggest which blue colour was used in the printer ink.

Give one reason for your answer.

[2 marks]

Blue colour

Reason

Mark scheme

Show the mark scheme The mark scheme for Question 3 is presented in a table with columns for question number, answers, extra information, mark, and AO/specification reference. For 03.1 the accepted answer is formulation. For 03.2 the answer is pencil, with the reason that the start line does not dissolve in the solvent. For 03.3 it awards marks for measuring the red spot distance as about 3.2 cm or 32 mm, the solvent distance as 8.0 cm or 80 mm, substituting into the Rf calculation, and obtaining 0.4. For 03.4 the accepted blue colour is prussian, with the reason that its Rf value is the closest to the printer ink value; the total for Question 3 is 9 marks.

Question 3

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 formulation 1 AO1

5.8.1.2

AO /

Spec. Ref.

03.2 pencil 1 AO3

5.8.1.3

(reason) RPA12

(so) the start line does not 1

dissolve in the solvent

AO /

Spec. Ref.

03.3 (distance moved by red colour) allow a value in the range 3.1 to 1 AO2

3.2 (cm) 3.3 (cm) 5.8.1.3

or RPA12

32 (mm) allow a value in the range 31 to

33 (mm)

(distance moved by solvent)

8.0 (cm) 1

or

80 (mm)

3.2 32 allow correct use of incorrectly 1

(Rf =) or determined distance(s)

8.0 80

= 0.4 1

AO /

Spec. Ref.

03.4 prussian allow 0.88 1 AO3

5.8.1.3

(prussian) has the closest Rf 1 RPA12

value (to the colour in the printer

ink)

Total Question 3 9

How to answer it

Printer Ink Chromatography

What this question tests

This question checks your knowledge of formulations, how to set up a chromatography experiment, how to calculate Rf values, and how to use a table of values to identify an unknown colour. It is mainly about recall, using a formula, and matching data.

Question 03.1 — Naming a useful mixture

✅ Correct answer

Formulation

This is worth 1 mark for the exact term.

💡 Key knowledge

  • A formulation is a mixture designed as a useful product.
  • Printer ink is an example of a formulation because it is made for a specific purpose.
  • Other common examples include paints, fuels, medicines, and fertilisers.

🧠 Exam technique

  • Read the wording carefully: “designed as a useful product” is the clue for formulation.
  • This is a single-word recall question, so spell it clearly.

❌ Common errors

  • Formula is wrong — that means the chemical formula of a substance.
  • Fraction is wrong — that is a part of a mixture separated by distillation.

Question 03.2 — Drawing the start line in chromatography

What to use, and why

✅ Correct answer

Pencil

Reason: the start line should not dissolve in the solvent.

This is 2 marks: 1 for pencil, 1 for the reason.

💡 Key knowledge

  • Pencil contains graphite, which does not dissolve in the solvent.
  • If you use pen, the ink may dissolve and travel up the paper, ruining the chromatogram.
  • The start line must stay fixed so you can measure movement accurately.

🧠 Exam technique

  • Give both parts: the object and the reason.
  • A good full-mark response is: pencil because it does not dissolve in the solvent .
  • Marks are often lost if students say only “graphite” without explaining why it is suitable.

❌ Common errors

  • Pen is a common wrong answer because the ink can dissolve.
  • Saying “it is clearer” or “it is stronger” does not answer the chemistry point.
  • The examiner wants the idea that the line must stay in place and not move with the solvent.

Question 03.3 — Calculating the Rf value of the red colour

📐 Calculation: step by step

  1. Measure the distance moved by the red spot: about 3.2 cm (acceptable range 3.1–3.3 cm).
  2. Measure the distance moved by the solvent front: about 8.0 cm.
  3. Use the formula: Rf = distance moved by colour ÷ distance moved by solvent
  4. Substitute the values: Rf = 3.2 ÷ 8.0
  5. Calculate: Rf = 0.4

✅ Correct answer

Distance moved by red colour: 3.2 cm

Distance moved by solvent: 8.0 cm

Rf = 0.4

Full marks come from the correct measurements, the formula, and the final answer.

💡 Key knowledge

  • Rf is a ratio, so it has no units.
  • It tells you how far a substance moved compared with the solvent front.
  • Similar substances often have similar Rf values under the same conditions.

🧠 Exam technique

  • Always measure from the start line to the centre of the spot and to the solvent front.
  • Use the same units for both distances; then the units cancel in the ratio.
  • Give your answer to a sensible number of decimal places, usually 0.4 here.
  • The mark scheme allows a small range for the spot distance, so an approximate ruler measurement is fine.

❌ Common errors

  • Measuring from the bottom of the paper instead of the start line.
  • Using the wrong distance for the spot, or measuring to the edge instead of the centre.
  • Forgetting to divide by the solvent distance.
  • Writing 0.4 cm — Rf has no units.

Question 03.4 — Identifying the blue colour from Rf data

✅ Correct answer

Blue colour: Prussian

Reason: it has the closest Rf value to 0.86.

The table value for Prussian is 0.88, which is nearest to 0.86.

💡 Key knowledge

  • To identify an unknown spot, compare its Rf with the values in the table.
  • The best match is the value that is closest, not necessarily exactly the same.
  • Here, 0.86 is closest to 0.88, so the blue is Prussian.

🧠 Exam technique

  • State both the name and the reason for both marks.
  • A strong answer is: Prussian, because its Rf value of 0.88 is closest to 0.86 .
  • Always compare the numbers directly — this is a matching question, not a calculation.

❌ Common errors

  • Choosing Ultramarine because it is blue in name, not because of the Rf value.
  • Saying “it is the same as 0.86” — it is not exactly the same, but it is the closest.
  • Ignoring the table and using guesswork.

Quick summary: how the marks are awarded

💡 Key facts to remember

  • Formulation = a useful mixture.
  • Pencil is used for a chromatography start line because it does not dissolve.
  • Rf = distance moved by colour ÷ distance moved by solvent.
  • Use the closest Rf value to identify an unknown substance.

🧠 Top-mark advice

  • Use the exact chemistry term where needed.
  • For explanations, give the science reason, not just a description.
  • For calculations, show the numbers, the substitution, and the final answer.
  • For data questions, compare values clearly and choose the closest match.

Topics

Chemistry · C8: Chemical Analysis

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.