AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2021: Question 7

12 marks · Standard Demand difficulty · Extended Answer

This question covers the reactions of acids, including pH changes, state symbols, observations of reactions with carbonates, ionic formulae, and planning a method to produce a pure, dry sample of a soluble salt.

Practise this question

Question

The image shows a series of chemistry questions numbered 07.1 to 07.6. It includes multiple-choice questions about pH and indicators, a request for a state symbol, a request for observations of a reaction between zinc carbonate and nitric acid, a multiple-choice question on the formula of zinc nitrate, and a 6-mark extended response question asking for a method to produce a pure, dry sample of copper chloride.
Question text

07 Acids react to produce salts.

Universal indicator is added to water and then nitric acid is added to the mixture.

07.1 Give the colour change when nitric acid is added to the mixture of

universal indicator and water.

[1 mark]

Tick ( ) one box.

Blue to red

Green to purple

Green to red

Red to purple

07.2 What happens to the pH of water when nitric acid is added?

[1 mark]

Tick ( ) one box.

Decreases

Stays the same

Increases

07.3 What is the state symbol for nitric acid?

[1 mark]

Zinc carbonate reacts with nitric acid.

The word equation for the reaction is:

zinc carbonate + nitric acid → zinc nitrate + water + carbon dioxide

white solid colourless

solution

07.4 Give two observations that would be made when zinc carbonate is added to nitric acid

until the zinc carbonate is in excess.

[2 marks]

07.5 The formula of the zinc ion is Zn2+

The formula of the nitrate ion is NO –

What is the formula for zinc nitrate?

[1 mark]

Tick ( ) one box.

ZnNO3

Zn(NO3)2

Zn2NO3

Zn2(NO3)2 26

07.6 Acids react with insoluble metal oxides to produce salts.

Plan a method to produce a pure, dry sample of the soluble salt copper chloride from

an acid and a metal oxide.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme provides the answers for questions 07.1 through 07.6. It lists the correct colour change, pH change, state symbol, and observations for the reaction. It also provides the correct chemical formula and a detailed 6-mark level-based rubric for the practical method of producing a soluble salt.

AO /

Question Answers Extra information Mark

Spec. Ref.

07.1 green to red 1 AO1

5.4.2.4

07.2 decreases 1 AO1

5.4.2.4

07.3 (aq) allow aq 1 AO1

5.2.2.2

ignore aqueous

ignore HNO3

07.4 any two from: 2 AO3

5.4.2.2

• (white) solid disappears 5.4.2.3

• fizzing or bubbles (of gas) or allow a gas is produced

effervescence

• (then) stops fizzing

• (white) solid left at the end /

bottom

ignore colourless solution

07.5 Zn(NO3)2 1 AO2

5.1.1.1

5.4.2.2

AO /

Question Answers Mark

Spec. Ref.

07.6 Level 3: The method would lead to the production of a valid 5–6 AO1

outcome. The key steps are identified and logically sequenced. 5.4.2.2

5.4.2.3

Level 2: The method would not necessarily lead to a valid 3–4 RPA8

outcome. Most steps are identified, but the method 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:

• react hydrochloric acid

• (with) copper oxide

• in a suitable container

• warm (hydrochloric) acid

• add copper oxide

• until is in excess

or

until solid remains

• stir

• filter excess copper oxide

• pour solution / filtrate into evaporating basin

• use of water bath

or

use of electric heater

• to heat gently

or

partially evaporate

• leave to cool / crystallise

For level 3 the correct chemicals must have been selected.

Total 12

How to answer it

Acids, Salts, and Chemical Reactions

What this question tests

This question assesses your understanding of acids and pH, the observations made during chemical reactions, writing chemical formulas by balancing charges, and the Required Practical for preparing a pure, dry sample of a soluble salt.

Parts 07.1, 07.2 & 07.3

The Basics of Acids

💡 Key Knowledge

  • Water is neutral (pH 7), so Universal Indicator is green.
  • Acids have a pH less than 7 and turn Universal Indicator red.
  • (aq) stands for aqueous, meaning "dissolved in water". All common acids in the lab are aqueous.

✅ Correct Answers

  • 07.1: Green to red
  • 07.2: Decreases
  • 07.3: (aq)
1 Mark each

❌ Common Errors

In 07.2, students often think "more acidic" means an "increase" in pH. Remember: Higher acidity = Lower pH number.

Part 07.4

Observations of Reactions

Zinc Carbonate + Nitric Acid

🧠 Exam Technique

An observation is something you see, hear, or feel. Don't just name the product (e.g., "carbon dioxide is made"); describe the evidence!

  • Instead of "CO₂", write "fizzing" or "bubbles".
  • Instead of "it reacts", write "solid disappears".

✅ Correct Answers (Any two)

  • Fizzing / bubbles / effervescence
  • (White) solid disappears
  • (White) solid remains at the bottom (when in excess)
  • The mixture stops fizzing
2 Marks
Part 07.5

Writing Chemical Formulas

Zinc Nitrate

📐 Step-by-Step Logic

  1. Identify the ions: Zinc is Zn²⁺ and Nitrate is NO₃⁻ .
  2. The total charge must be zero.
  3. You need two Nitrate ions (2 × 1-) to balance one Zinc ion (1 × 2+).
  4. Because Nitrate is a polyatomic ion (a group of atoms), you must use brackets.

✅ Correct Answer

Zn(NO₃)₂

1 Mark

❌ Common Errors

Writing ZnNO₃₂ without brackets. This would mean 1 Zinc, 1 Nitrogen, and 32 Oxygens! Always bracket the ion if you need more than one of it.

Part 07.6

Required Practical: Making a Soluble Salt

Target: Pure, dry Copper Chloride

🧠 Examiner Insight

To get 5-6 marks, your method must be logical and use the correct chemicals. If you use the wrong acid, you cannot reach the top marks.

🧪 Choosing Chemicals

  • Salt needed: Copper Chloride
  • Metal Oxide: Copper Oxide
  • Acid needed: Hydrochloric Acid (to provide the chloride ions)

✅ The Perfect Method

  1. Measure a set volume of hydrochloric acid into a beaker.
  2. Gently warm the acid (to speed up the reaction).
  3. Add copper oxide and stir.
  4. Keep adding copper oxide until it is in excess (solid remains at the bottom). This ensures all acid is used up.
  5. Filter the mixture using a funnel and filter paper to remove the excess copper oxide.
  6. Pour the filtrate (blue solution) into an evaporating basin.
  7. Heat gently over a water bath until half the water has evaporated.
  8. Leave to cool and crystallise. Pat the crystals dry with filter paper.
6 Marks

❌ Common Errors

  • Heating to dryness: Don't evaporate all the water with a Bunsen burner. This can cause the salt to spit or decompose. Always say "heat until crystals start to form" or "partially evaporate".
  • Wrong Acid: Using Sulfuric acid would make Copper Sulfate, not Copper Chloride!

Topics

Chemistry · C4: Chemical Changes

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.