AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2022: Question 5

9 marks · Standard Demand difficulty · Short Answer

Describe observations and separation techniques for making copper sulfate, and calculate the mass of crystals formed using a solubility graph.

Practise this question

Question

A chemistry exam paper featuring questions about the reaction between copper carbonate and sulfuric acid. It includes a solubility curve graph (Figure 13) for ammonium nitrate, plotting mass in grams per 100 cm³ of water against temperature in degrees Celsius. The graph shows a positive curve starting at approximately 23g at 0°C and rising to over 100g at 100°C. The final part of the question asks students to determine the mass of crystals formed when cooling from 80°C to 20°C.
Question text

05 This question is about salts.

Green copper carbonate and sulfuric acid can be used to produce

blue copper sulfate crystals.

05.1 Excess copper carbonate is added to sulfuric acid.

Give three observations you would make.

[3 marks]

05.2 How can the excess copper carbonate be removed?

[1 mark]

05.3 The pH of the solution changes during the reaction.

What is the pH of the solution at the end of the reaction?

[1 mark]

pH =

05.4 Copper carbonate and sulfuric acid react to produce copper sulfate.

What type of reaction is this?

[1 mark]

05.5 Ammonium nitrate is a salt.

Figure 13 shows the maximum mass of ammonium nitrate that can dissolve

in 100 cm3 of water at different temperatures.

Figure 13

A student adds ammonium nitrate to water at 80 °C until no more dissolves.

The student cools 100 cm3 of this solution of ammonium nitrate from 80 °C to 20 °C to

produce crystals of ammonium nitrate.

Determine the mass of ammonium nitrate that crystallises on cooling 100 cm3 of this

solution from 80 °C to 20 °C

[3 marks]

Mass = g

Mark scheme

Show the mark scheme The mark scheme for question 5. It lists acceptable observations for the reaction such as 'blue solution formed', 'fizzing', and 'solid left at the end'. It identifies the separation method as 'filtration' and the reaction type as 'neutralisation'. For the calculation in 05.5, it awards marks for reading 83g at 80°C, 32g at 20°C, and calculating the difference as 51g.

Question 5

AO /

Question Answers Extra information Mark

Spec. Ref.

05.1 any three from: 3 AO2

AO3

• green solid / powder ignore green copper carbonate 5.4.2.2

5.4.2.3

• colourless solution RPA8

• blue solution formed allow colour (of solution)

changes

• copper carbonate disappears allow solid disappears

• fizzing / effervescence ignore gas

or

bubbles (of gas)

• stops fizzing allow fizzing slows down

• solid / powder left at the end

or

copper carbonate left at the

end

allow (container) gets hot

or

allow temperature increases

AO /

Spec. Ref.

05.2 filtration 1 AO1

or 5.4.2.3

filter RPA8

AO /

Spec. Ref.

05.3 7 1 AO1

5.4.2.3

5.4.2.4

RPA8

AO /

Spec. Ref.

05.4 neutralisation allow exothermic 1 AO1

5.4.2.2

5.4.2.4

RPA8

AO /

Spec. Ref.

05.5 83 (g at 80 °C) allow a value in range 82–84 (g 1 AO2

at 80 °C)

32 (g at 20 °C) allow a value in range 32–33 (g 1 AO2

at 20 °C)

(83–32 =) 51 (g) allow a correct calculation using 1 AO3

incorrectly read values for mass

at 80 °C and/or 20 °C 5.4.2.3

Total Question 5 9

How to answer it

Making Salts and Solubility Curves

What this question tests

This question assesses your knowledge of Required Practical 8 (Making Salts), chemical observations, pH changes during neutralisation, and your ability to interpret and calculate data from a solubility curve.

Part (05.1)

Observations of the reaction

Correct Answers (Any 3)

  • Fizzing / Bubbles / Effervescence
  • Blue solution formed
  • Green solid disappears
  • Solid/powder left at the end (excess)
  • The container gets hot

Key Knowledge

Copper Carbonate + Sulfuric Acid → Copper Sulfate + Water + Carbon Dioxide

  • CO₂ causes the fizzing.
  • Copper Sulfate is a blue solution.
  • Green powder is the copper carbonate.

Exam Technique

When asked for observations, describe what you would see or feel. Don't just name the products. For example, instead of saying "carbon dioxide is made," say "you would see bubbles."

Parts (05.2) & (05.3)

Separation and pH

Correct Answers

05.2: Filtration (or filter)

05.3: pH 7

Why pH 7?

Because excess copper carbonate was added, all the sulfuric acid has been used up. The resulting solution is neutral.

Common Error

Students often forget that "excess" means the acid is completely neutralised. If the acid wasn't fully reacted, the pH would be lower than 7.

Part (05.4)

Reaction Type

Correct Answer

Neutralisation (also accept exothermic as the temperature increases).

Part (05.5)

Solubility Calculation

Step-by-Step Calculation

  1. Find solubility at 80 °C: Look at the x-axis for 80, go up to the curve, then across to the y-axis.
    Value = 83 g (Accept 82–84 g).
  2. Find solubility at 20 °C: Look at the x-axis for 20, go up to the curve, then across to the y-axis.
    Value = 32 g (Accept 32–33 g).
  3. Calculate the difference: Subtract the lower value from the higher value to find how much "fell out" of the solution as crystals.
    83 g - 32 g = 51 g.

Final Answer: 51 g

How marks are awarded

  • 1 Mark: Correct reading at 80 °C
  • 1 Mark: Correct reading at 20 °C
  • 1 Mark: Correct subtraction of your two values

Calculation Traps

Always check the scale of the graph. On this y-axis, each small square represents 2g. Misreading the scale is the most common way to lose marks here.

Visualising the Practical (RPA8)

If you were asked to draw the apparatus for removing the excess solid, you should draw:

  • A filter funnel sitting in a conical flask.
  • Filter paper inside the funnel (shown as a V-shape).
  • The "excess copper carbonate" labelled as residue in the paper.
  • The "copper sulfate solution" labelled as filtrate in the flask.

Topics

Chemistry · C4: Chemical Changes · C8: Chemical Analysis

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.