AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2023: Question 6

12 marks · Standard Demand difficulty · Extended Answer

Identify ions and indicators for acidic solutions, interpret solubility graphs, and describe a method to measure the volume of gas produced in a reaction.

Practise this question

Question

The image shows a series of chemistry exam questions. Question 6.1 asks for the ion that makes a solution acidic. 6.2 asks for an indicator and its result in an acidic solution. Figure 14 is a line graph showing the mass of carbon dioxide dissolved in 1 dm³ of water against temperature; the curve starts at approximately 3.4 g at 0°C and slopes downwards to about 0.6 g at 60°C. Questions 6.3 and 6.4 ask for interpretations of this graph. 6.5 asks for a state symbol in a chemical equation. 6.6 shows diagrams of a measuring cylinder, conical flask, gas syringe, and digital balance, asking for a method to investigate the volume of gas produced from different masses of calcium carbonate.
Question text

06 This question is about carbon dioxide.

Carbon dioxide is soluble in water and forms an acidic solution.

06.1 Which ion makes the solution acidic?

[1 mark]

06.2 Name an indicator that could be used to test if the solution is acidic.

Give the result of the test.

[2 marks]

Indicator

Result

Figure 14 shows the mass of carbon dioxide that will dissolve in 1 dm3 of water

at different temperatures.

Figure 14

06.3 How does the solubility of carbon dioxide change as the temperature of the

water increases?

*27* [1 mark]

Tick ( ) one box.

The solubility decreases

The solubility does not change

The solubility increases 29

06.4 Carbon dioxide dissolves in water to form an acidic solution.

How does the pH of the solution change as the temperature of the water increases?

Use Figure 14.

[1 mark]

Tick ( ) one box.

pH of the solution decreases

pH of the solution does not change

pH of the solution increases

Calcium carbonate reacts with hydrochloric acid to produce carbon dioxide.

The equation for the reaction is:

CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(x)

06.5 What is the state symbol (x) in the equation?

[1 mark]

Tick ( ) one box.

(aq) (g) (l)30 (s)

06.6 Figure 15 shows equipment a student used for an investigation.

Figure 15

The student investigated the volume of carbon dioxide produced when different

masses of calcium carbonate react with hydrochloric acid.

Describe a method the student could use.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme for question 6. 06.1: hydrogen / H+. 06.2: universal indicator (red/orange/yellow), litmus (red), or methyl orange (red). 06.3: solubility decreases. 06.4: pH increases. 06.5: (l). 06.6: A level-based mark scheme for a 6-mark practical method. Level 3 (5-6 marks) requires a logically sequenced method leading to a valid outcome. Indicative content includes measuring mass of calcium carbonate, using a balance, adding to a conical flask, measuring acid volume, using a gas syringe, and repeating with different masses.

Question 6

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 hydrogen / H+ 1 AO1

5.4.2.4

AO /

Spec. Ref.

06.2 MP2 is dependent upon MP1 AO1

being awarded 5.4.2.4

(indicator) universal ignore pH meter 1

(result) (green to) red / orange / 1

yellow

OR

(indicator) (blue) litmus (1)

(result) (turns) red (1)

OR

(indicator) methyl orange (1)

(result) (turns) red (1)

AO /

Spec. Ref.

06.3 the solubility decreases 1 AO3

5.3.2.5

AO /

Spec. Ref.

06.4 pH of the solution increases 1 AO3

5.3.2.5

5.4.2.4

AO /

Spec. Ref.

06.5 (l) 1 AO2

18 5.2.2.2

AO2.2

AO /

Question Answers Mark

Spec. Ref.

Level 3: The method would lead to the production of a valid 5–6

06.6 AO3

outcome. All key steps are identified and logically sequenced.

5.3.1.3

5.4.2.2

Level 2: The method would not necessarily lead to a valid 3–4

outcome. Most steps are identified, but the plan is not fully logically

sequenced.

Level 1: The method would not lead to a valid outcome. Some 1–2

relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative Content:

• measure a (stated) mass of calcium carbonate

• use a balance

• add calcium carbonate into a conical flask

• measure a (stated) volume of hydrochloric acid

• use a measuring cylinder

• add hydrochloric acid to the conical flask

• immediately place the stopper (and delivery tube) in the conical

flask

• record the total volume of carbon dioxide gas

or

record volume of carbon dioxide collected in set time

or

time taken to collect fixed volume of gas

• collected in the gas syringe

• repeat

• repeat method with different masses of calcium carbonate

Total Question 6 12

How to answer it

Carbon Dioxide: Solubility, pH, and Practical Methods

What this question tests

This question assesses your understanding of acids and bases (ions and indicators), interpreting graphical data regarding solubility, identifying state symbols, and designing a valid experimental method to measure gas production.

Part (06.1) & (06.2)

Acidity and Indicators

Identifying acidic solutions

Correct Answers

  • 06.1: Hydrogen ion / H⁺
  • 06.2 Indicator: Universal Indicator or Blue Litmus Paper or Methyl Orange
  • 06.2 Result: Red / Orange / Yellow (for UI) or Turns Red (for Litmus/Methyl Orange)

Key Knowledge

All acids release H⁺ ions in aqueous solution. This is what makes a solution "acidic". Indicators change colour depending on the concentration of these ions.

Exam Technique

In 06.2, the second mark is dependent on the first. If you name the wrong indicator, you cannot get the result mark. Always choose the most common indicators you know well (like Litmus or Universal Indicator).

Part (06.3) & (06.4)

Solubility Trends

Interpreting Figure 14

Correct Answers

  • 06.3: The solubility decreases
  • 06.4: pH of the solution increases

How to read the graph

Look at the line in Figure 14. As you move right (higher temperature), the line goes down (lower mass of CO₂). This means solubility is decreasing.

Common Error: The pH Trap

Many students think "less CO₂" means "less pH". This is wrong!

  • Less dissolved CO₂ = Less Acidic solution.
  • Less acidic = Higher pH (moving closer to 7).
Part (06.5)

State Symbols

Chemical Equations

Correct Answer

(l) - This stands for liquid.

Quick Reference

  • (s): Solid (e.g., Calcium Carbonate)
  • (l): Liquid (Pure substances like H₂O)
  • (g): Gas (e.g., CO₂)
  • (aq): Aqueous (Dissolved in water, e.g., HCl)
Part (06.6)

6-Mark Practical Method

Investigating Gas Volume vs. Mass

How to get 6 Marks (Level 3)

To reach the top marks, your method must be logically sequenced and lead to a valid outcome. You must use the equipment shown in Figure 15 (Balance, Measuring Cylinder, Conical Flask, Gas Syringe).

Step-by-Step Method

  1. Use the balance to measure a specific mass of calcium carbonate.
  2. Use the measuring cylinder to measure a fixed volume of hydrochloric acid.
  3. Add the calcium carbonate into the conical flask.
  4. Add the hydrochloric acid to the flask and immediately attach the stopper/bung connected to the gas syringe.
  5. Record the total volume of gas collected in the syringe once the reaction stops (no more bubbles).
  6. Repeat the experiment using different masses of calcium carbonate (e.g., 0.1g, 0.2g, 0.3g).
  7. Keep the volume and concentration of acid the same (control variables).

Examiner Insight: Common Pitfalls

  • Forgetting the bung: If you don't mention sealing the flask, the gas escapes and the method is invalid.
  • Vague measurements: Don't just say "add acid". Say "measure 25 cm³ of acid using a measuring cylinder".
  • Missing the "Repeat": To investigate "different masses", you must explicitly state that you will change the mass and repeat the steps.

Diagram Description

If you were to draw this, you would show a conical flask with a rubber bung in the top. A delivery tube would lead from the bung into the nozzle of a horizontal gas syringe. The syringe plunger should be shown moving outwards as gas enters.

Topics

Chemistry · C4: Chemical Changes · C3: Quantitative Chemistry · C6: The Rate and Extent of Chemical Change

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.