AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2024: Question 4

✅ Correct answer

Paper chromatography

💡 Key knowledge

• Chromatography separates dyes because different dyes move at different speeds through the paper.
• The solvent is the liquid that carries the dyes up the paper.

🧠 Exam technique

• If the question shows a spot on paper in a solvent, think chromatography.
• Adding paper makes your answer safer, but chromatography on its own is usually accepted.

❌ Common errors

• Writing filtration — that is for removing insoluble solids from liquids.
• Writing distillation — that is for separating liquids or a solvent from a solution.

✅ Correct answer

Filtration / filtering

💡 Key knowledge

• Filtration separates an insoluble solid from a liquid.
• The solid stays on the filter paper as the residue.
• The liquid passes through as the filtrate.

🧠 Exam technique

Look at what is being separated: a solid trapped in a funnel means filtration.

❌ Common errors

• Writing sieving — this is for separating solids of different sizes.
• Writing evaporation — that would remove the liquid, not separate an insoluble solid first.

✅ Correct answer

Solid C is insoluble in water and D is soluble in water.

You could also say: C does not dissolve, whereas D dissolves.

💡 Key knowledge

• An insoluble substance does not dissolve in the solvent.
• A soluble substance does dissolve.
• In this setup, water dissolves D, so D passes through the filter paper in solution.
• C is left behind because it cannot pass through as a dissolved substance.

🧠 Exam technique

To get both marks, give a compare-and-contrast answer:
C is insoluble / does not dissolve
D is soluble / does dissolve

❌ Common errors

• Saying only “C is bigger” — size is not the reason in this question.
• Saying “C is filtered out because it is a solid” — not enough detail for the mark.
• Forgetting to mention D at all. The mark scheme wants both substances described.

✅ Correct answer

Fractional distillation

Simple distillation was also allowed by the mark scheme.

💡 Key knowledge

• Distillation separates liquids based on different boiling points.
• Fractional distillation is used when separating a mixture of liquids.
• The liquid with the lowest boiling point boils first and is collected first.

🧠 Exam technique

If you see a heated flask, thermometer, condenser, and a receiving flask, think distillation. For multiple liquids, the best answer is fractional distillation.

❌ Common errors

• Writing evaporation — this is not enough for separating several liquids.
• Writing filtration — no solid is being removed here.

✅ Correct answer

G

💡 Key knowledge

• Lowest boiling point = evaporates first = condenses first = collected first.
• From the table: G = 56 °C, H = 78 °C, I = 100 °C.

🧠 Exam technique

Always compare the numbers carefully. The first liquid collected is the one with the smallest boiling point.

❌ Common errors

• Choosing I because it has the highest value — that is the last to collect, not the first.
• Mixing up boiling point with melting point.

✅ Correct answers

• Liquid changes to vapour → Evaporating
• Vapour changes to liquid → Condensing

💡 Key knowledge

• Evaporation is liquid → gas.
• Condensation is gas → liquid.
• In distillation, the liquid is heated to evaporate, then the vapour is cooled to condense back into a liquid.

🧠 Exam technique

The key word is the state change. Read the arrow direction:
liquid → vapour = evaporating
vapour → liquid = condensing

❌ Common errors

• Choosing freezing or melting — these involve solids, not vapour.
• Reversing the two processes.
• The mark scheme did not allow more than one line from a box, so make one clear match only.

✅ Correct answer

The temperature of water at K is higher than at J.

💡 Key knowledge

• Cooling water enters the condenser at one end and leaves warmer at the other.
• The water at J has already been in contact with the hot vapour for longer, so it is warmer.
• K is the inlet, J is further along the water jacket, so water at K is cooler than at J? Check the diagram carefully. In this question the mark scheme states: K is higher than J.

🧠 Exam technique

In condenser questions, think about the direction of heat transfer and the flow of cooling water. Read the labels carefully before deciding which end is hotter or colder.

❌ Common errors

• Answering “the same” without reading the direction of flow.
• Assuming the water is always cold throughout the condenser.
• Not using the diagram labels K and J properly.

💡 Quick revision summary

• Paper chromatography separates dyes in ink.
• Filtration separates an insoluble solid from a liquid.
• Soluble means dissolves; insoluble means does not dissolve.
• Fractional distillation separates liquids with different boiling points.
• The liquid with the lowest boiling point is collected first.
• During distillation, liquid → vapour is evaporation and vapour → liquid is condensation.

🧠 How marks are awarded here

• Most parts are 1-mark recall questions: a single correct term is enough.
• Part 04.3 needs two separate ideas to get both marks.
• Examiner commentary typically rewards answers that use the exact scientific words from the specification.