AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), June 2025: Question 3
9 marks · Low Demand difficulty · Short Answer
Investigate the reaction of magnesium with oxygen, completing a word equation, identifying oxidation, calculating mass changes, identifying anomalies on a graph, and calculating a mean.
Practise this questionQuestion
Question text
03 A student investigated the reaction of magnesium with oxygen.
Figure 6 shows the apparatus.
Figure 6
This is the method used.
1. Measure the mass of an empty crucible.
2. Add 0.10 g of magnesium to the crucible.
3. Heat the crucible and contents for 5 minutes.
4. Allow to cool and measure the mass of the crucible and contents.
5. Repeat steps 1 to 4 using different masses of magnesium.
03.1 Complete the word equation for the reaction.
[1 mark]
magnesium + oxygen →
03.2 Complete the sentence.
Choose the answer from the box.
[1 mark]
decomposed oxidised reduced
When magnesium reacts with oxygen, the magnesium is .
Table 3 shows the measurements for one of the experiments.
Table 3
Mass in grams
Empty crucible 20.25
Crucible and magnesium before heating 20.55
Crucible and contents after heating 20.75
03.3 Calculate the mass of magnesium in the crucible before heating.
[1 mark]
Mass of magnesium = g
03.4 Why does the reaction result in an increase in the mass of the contents of
the crucible?
[1 mark]
Tick ( ) one box.
A solid reacts with a gas to produce a solid.
Some of the product escapes from the crucible.
The reactants have a greater mass than the product.16
03.5 The student determined the mass of the contents of the crucible after heating each
mass of magnesium.
Figure 7 shows the results.
Figure 7
Draw a ring around the anomalous result in Figure 7.
[1 mark]
03.6 The student did the experiment using 0.60 g of magnesium four times.
Table 4 shows the results.
Table 4
Test 1 Test 2 Test 3 Test 4 Mean
Mass of the contents of the crucible
0.96 0.93 0.92 0.95 X
after heating in grams
Calculate mean value X.
[2 marks]
Mean value X = g
03.7 The student used a Bunsen burner instead of a water bath to heat the crucible.
Why did the student use a Bunsen burner?
[1 mark]
Tick ( ) one box.
A Bunsen burner heats up the crucible more slowly.
A water bath is not hot enough.
The crucible would dissolve in a water bath.18
03.8 A different student did the investigation.
The student heated the crucible for 1 minute instead of for 5 minutes.
The student obtained different results.
Suggest one reason why the student obtained different results.
[1 mark]
Mark scheme
Show the mark scheme
Question 3
AO /
Question Answers Mark
Spec. Ref.
03.1 magnesium + oxygen → magnesium oxide 1 AO2
5.4.1.1
allow MgO for magnesium oxide
AO /
Question Answers Extra information Mark
Spec. Ref.
03.2 oxidised 1 AO1
5.4.1.1
AO /
Spec. Ref.
03.3 0.30 (g) allow 0.3 (g) 1 AO2
5.3.1.3
AO /
Spec. Ref.
03.4 a solid reacts with a gas to 1 AO3
produce a solid 5.3.1.3
AO /
Spec. Ref.
03.5 ring around point 0.25, 0.35 1 AO3
5.3.1.3
AO /
Spec. Ref.
03.6 (mean =) 3.76 1 AO2
0.96 + 0.93 + 0.92 + 0.95 allow (mean =) 5.3.1.3
= 0.94 (g) 1
AO /
Spec. Ref.
03.7 a water bath is not hot enough 1 AO3
5.3.1.3 11
AO /
Spec. Ref.
03.8 some of the magnesium did not allow the reaction was 1 AO3
react incomplete 5.3.1.3
allow none of the magnesium
reacted
allow there was no reaction
Total Question 3 9
How to answer it
Reaction of Magnesium with Oxygen & Mass Changes
What this question tests
- Word equations: Recalling the product formed when a group 2 metal burns in air.
- Types of reaction: Identifying oxidation in terms of gaining oxygen.
- Conservation of mass: Explaining apparent mass gains when an open system reacts with atmospheric gases.
- Practical data handling: Calculating sample mass by difference, finding an anomaly on a scatter graph, and calculating a mean from repeated trials.
- Laboratory equipment & variables: Evaluating heating apparatus and understanding the effect of heating duration on completion of reactions.
Word Equation for Burning Magnesium
Completing the chemical word equation [1 mark]
✅ Correct Answer
magnesium + oxygen → magnesium oxide
Mark allocation: 1 mark for naming magnesium oxide (chemical formula MgO is also accepted).
❌ Common Errors
- Writing "magnesium dioxide" (magnesium forms a 2+ ion and oxygen forms a 2- ion, so the formula is simply MgO).
- Writing "magnesium gas" or confusing the product with "magnesium hydroxide".
Oxidation Reaction
Identifying reaction type from a given list [1 mark]
✅ Correct Answer
When magnesium reacts with oxygen, the magnesium is oxidised.
💡 Key Knowledge
Oxidation:
- In terms of oxygen: gain of oxygen.
- In terms of electrons (OIL RIG): loss of electrons (Mg → Mg²⁺ + 2e⁻).
- Reduction: Loss of oxygen or gain of electrons.
Calculating Mass of Magnesium Before Heating
Subtraction using balance measurements [1 mark]
📐 Step-by-Step Calculation
- Identify empty crucible mass = 20.25 g
- Identify crucible + magnesium mass = 20.55 g
- Subtract: 20.55 g − 20.25 g = 0.30 g (or 0.3 g)
🧠 Exam Technique
Read table headings carefully. The question asks for the mass before heating, so you must ignore the final row ("after heating: 20.75 g") for this specific step.
Explaining the Apparent Mass Increase
Understanding the Law of Conservation of Mass [1 mark]
✅ Correct Answer
Tick box 1: A solid reacts with a gas to produce a solid.
💡 Key Knowledge: Apparent Mass Changes
- Total mass is always conserved in a chemical reaction.
- If a reaction takes place in an open crucible, gas from the air (oxygen) is added to the solid, making the measured mass inside the crucible increase.
- If the mass had decreased, it would usually mean a gas escaped (e.g. CO₂ from thermal decomposition).
Identifying Anomalous Data on a Graph
Graph interpretation and outlier detection [1 mark]
✅ Correct Answer
Draw a ring around the fourth plotted point at coordinate: (0.25, 0.35).
Examiner description: On the grid, all points lie along a straight line of best fit through the origin, except the point at x = 0.25 g and y = 0.35 g, which sits visibly below the trend.
🧠 Exam Technique
To identify an anomaly easily, visualise or lightly place a ruler along the points. The anomaly is the point furthest away from the obvious straight line or smooth curve formed by the other data points.
Calculating the Mean of Repeated Results
Finding the arithmetic mean from repeated tests [2 marks]
📐 Step-by-Step Calculation
- Sum the test values:
0.96 + 0.93 + 0.92 + 0.95 = 3.76 g
(Awards 1 method mark) - Divide by the number of values (4):
3.76 ÷ 4 = 0.94 g
(Awards 1 accuracy mark)
❌ Common Errors
- Dividing by 3 instead of 4.
- Rounding incorrectly or writing fewer/more decimal places than given in the data table (values were given to 2 decimal places).
Apparatus Choice: Bunsen Burner vs Water Bath
Evaluating heating apparatus [1 mark]
✅ Correct Answer
Tick box 2: A water bath is not hot enough.
💡 Key Knowledge
A water bath can only reach a maximum temperature of 100 °C (the boiling point of water). Magnesium requires very high temperatures (over 600 °C) to overcome the activation energy and ignite in oxygen.
Effect of Heating Time on Results
Explaining incomplete chemical reactions [1 mark]
✅ Correct Answer
Any one of the following:
- Some of the magnesium did not react
- The reaction was incomplete / not finished
- None of the magnesium reacted / there was no reaction
🧠 Exam Technique
When an experiment involves "heating to constant mass" or heating for a set time, reducing the time almost always leads to an incomplete reaction. State clearly that some reactant has not yet reacted!
Topics
Chemistry · C3: Quantitative Chemistry · C4: Chemical Changes
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.