AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2021: Question 1

10 marks · Standard Demand difficulty · Short Answer

A series of questions regarding the reaction of magnesium with chlorine, the decomposition of magnesium carbonate, and associated calculations of percentage mass and mean values.

Practise this question

Question

A chemistry exam page containing seven sub-questions (01.1 to 01.7) about magnesium reactions. It includes multiple-choice questions on reaction types and apparatus, a word equation completion, a mass prediction question, a percentage mass calculation, and a data analysis task involving a table of results for the decomposition of magnesium carbonate.
Question text

01 Magnesium is in Group 2 of the periodic table.

1.0 g of magnesium reacted with chlorine to produce magnesium chloride.

01.1 Which types of element react when magnesium reacted with chlorine?

[1 mark]

Tick ( ) one box.

A metal and a metal

A metal and a non-metal

A non-metal and a non-metal

01.2 Write the word equation for the reaction when magnesium reacts with chlorine.

[1 mark]

+ →

01.3 What apparatus was used to measure the mass of 1.0 g of magnesium?

[1 mark]

Tick ( ) one box.

Balance

Beaker

Ruler 3

01.4 What mass of magnesium chloride was produced?

[1 mark]

Tick ( ) one box.

*02* Less than 1.0 g

1.0 g

More than 1.0 g

01.5 Magnesium reacts with oxygen to produce magnesium oxide.

Calculate the percentage mass of magnesium in magnesium oxide (MgO).

Relative atomic mass (Ar): Mg = 24

Relative formula mass (Mr): MgO = 40

[2 marks]

Percentage mass of magnesium = %

Magnesium carbonate decomposes to produce magnesium oxide and carbon dioxide.

The word equation for the reaction is:

magnesium carbonate → magnesium oxide + carbon dioxide

Four students heated 2.00 g of magnesium carbonate for 10 minutes.

Table 1 shows the results.

Table 1

Mass of carbon dioxide produced in g

Student 1 Student 2 Student 3 Student 4 Mean

0.97 0.91 0.50 0.95 X

01.6 What is the most likely reason for Student 3’s anomalous result?

[1 mark]

Tick ( ) one box.

The student heated more than 2.00 g of magnesium carbonate.

The student heated the magnesium carbonate for less than 10 minutes.

The student used a higher temperature.

01.7 Calculate value X in Table 1.

Do not use the anomalous result.

Give your answer to 2 significant figures.

[3 marks]

X (2 significant figures) = g

Mark scheme

Show the mark scheme A table showing the mark scheme for questions 01.1 through 01.7. It lists the correct answers, provides extra information for marking, assigns marks for each part, and references Assessment Objectives and specification points.

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 a metal and a non-metal 1 AO1

5.1.2.1

5.1.2.3

5.3.1.1

01.2 magnesium + chlorine → allow Mg for magnesium 1 AO2

magnesium chloride allow Cl2 for chlorine 5.1.1.1

allow MgCl2 for magnesium 5.1.2.6

chloride

01.3 balance 1 AO1

5.3.1.3

01.4 more than 1.0 g 1 AO3

5.3.1.3

5.4.1.1

01.5 24 AO2

(% =) × 100 1

40 5.3.1.2

= 60 (%) 1

01.6 the student heated the 1 AO3

magnesium carbonate for less 5.3.1.3

than ten minutes

01.7 0.97 + 0.91 + 0.95 2.83 allow for 1 mark 1

or AO3

33 0.97 + 0.91 + 0.50 + 0.95 3.33

or

= 0.943333 (g) 4 4 1 AO2

= 0.8325 (g)

AO2

= 0.94 (g) allow an answer correctly 1

5.3.1.3

rounded to 2 significant figures

using values from the table

Total 10

How to answer it

Magnesium Reactions & Calculations

What this question tests

This question assesses your ability to identify bonding types, write word equations, understand the conservation of mass, calculate percentage composition by mass, and process experimental data by identifying anomalies and calculating means.

Part 01.1 & 01.2

Bonding and Equations

Correct Answers

  • 01.1: A metal and a non-metal
  • 01.2: magnesium + chlorine → magnesium chloride

Key Knowledge

Magnesium is in Group 2 (Metal). Chlorine is in Group 7 (Non-metal). When they react, they form an ionic bond.

Exam Technique: Word Equations

In a word equation, never use chemical symbols unless the question asks for a symbol equation. Ensure the product name ends correctly—metals reacting with non-metals usually end in -ide (e.g., Chloride, Oxide).

Part 01.3 & 01.4

Measuring Mass

Correct Answers

  • 01.3: Balance
  • 01.4: More than 1.0 g

Examiner Insight

For 01.4, many students incorrectly guess "1.0 g" thinking mass is always conserved. While mass is conserved, the 1.0 g only accounts for the magnesium. The chlorine added from the surroundings adds extra mass to the final solid product.

Common Error

Don't confuse a beaker (used for volume/holding liquids) with a balance (used for mass). Always look at the units: if it's in grams (g), you need a balance.

Part 01.5

Percentage Mass Calculation

Step-by-Step Calculation

Calculate the percentage of Magnesium in MgO:

  1. Identify the mass of the element: Ar of Mg = 24
  2. Identify the total mass of the compound: Mr of MgO = 40
  3. Use the formula: (Total Ar of element / Mr of compound) × 100
  4. Calculate: (24 / 40) × 100 = 60%
Award 1 mark for the correct substitution (24/40) and 1 mark for the final answer (60).
Part 01.6 & 01.7

Data Analysis: Means and Anomalies

Correct Answers

  • 01.6: The student heated the magnesium carbonate for less than 10 minutes.
  • 01.7: 0.94 g

Calculating the Mean (Value X)

  1. Identify the anomaly: Student 3's result (0.50) is much lower than the others (0.97, 0.91, 0.95). Exclude it!
  2. Sum the remaining values: 0.97 + 0.91 + 0.95 = 2.83
  3. Divide by the number of values: 2.83 / 3 = 0.94333...
  4. Round to 2 Significant Figures: 0.94 g

Calculation Traps

  • The "Divide by 4" Trap: If you include the anomaly, you will divide by 4 and get 0.83. This loses marks!
  • Significant Figures: The question explicitly asks for 2 sig figs. Writing "0.943" would lose the final mark.

Topics

Chemistry · C3: Quantitative Chemistry · C4: Chemical Changes · C8: Chemical Analysis

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.