AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2022: Question 2

8 marks · Standard Demand difficulty · Short Answer

Complete a dot and cross diagram for HCl, write a neutralization word equation, calculate mass using conservation of mass, read a thermometer, and identify exothermic reactions and ions in an alkali.

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Question

Question text

02 This question is about hydrogen chloride and sodium hydroxide.

02.1 A chlorine atom has 7 electrons in the outer shell.

A hydrogen atom has 1 electron in the outer shell.

Figure 4 represents part of a dot and cross diagram for a molecule of

hydrogen chloride.

Complete the dot and cross diagram.

Use dots (ο) and crosses (x) to represent electrons.

You should show only the electrons in the outer shells.

[2 marks]

Figure 4

02.2 Hydrogen chloride dissolves in water to produce hydrochloric acid.

Hydrochloric acid reacts with sodium hydroxide solution.

Complete the word equation for the reaction between hydrochloric acid and

sodium hydroxide.

[1 mark]

hydrochloric acid + sodium hydroxide → + water

Solutions of hydrochloric acid and sodium hydroxide are reacted and the

temperature change is recorded.

02.3 In the reaction, 3.65 g of hydrogen chloride reacts with 4.00 g of sodium hydroxide.

1.80 g of water is produced.

Calculate the mass of the other product.

[1 mark]

Mass = g

02.4 Figure 5 shows part of the thermometer used to measure the temperature.

Figure 5

What is the temperature reading on the thermometer?

[1 mark]

Temperature = °C

02.5 In the reaction, the temperature increases.

What type of reaction is happening when the temperature increases?

[1 mark]

02.6 Sodium hydroxide is an alkali.

Which two ions are in sodium hydroxide solution?

[2 marks]

Tick ( ) two boxes.

Cl– H+ Na+ O2– OH–

Mark scheme

Show the mark scheme

Question 2

AO /

Question Answers Extra information Mark

Spec. Ref.

02.1 allow any combination of circles, AO1

dots, crosses or e(–) 5.1.2.6

5.2.1.4

one shared pair in overlap 1

6 non-bonding electrons in outer do not accept extra electron(s) 1

shell of chlorine on outer shell of hydrogen

ignore any inner shell electrons

an answer of

scores 2 marks

AO /

Spec. Ref.

02.2 sodium chloride allow NaCl 1 AO2

5.4.2.2

AO /

Spec. Ref.

02.3 5.85 (g) 1 AO2

5.3.1.1

5.4.2.2

5.5.1.1

RPA10

AO /

Spec. Ref.

02.4 17.6 (°C) 1 AO2

5.4.2.2

5.5.1.1

RPA10

AO /

Spec. Ref.

02.5 exothermic (reaction) allow neutralisation (reaction) 1 AO2

5.5.1.1

RPA10

AO /

Spec. Ref.

02.6 Na+ 1 AO1

AO2

OH– 1 5.4.2.2

5.4.2.4

5.5.1.1

Total Question 2 8

How to answer it

Hydrogen Chloride and Sodium Hydroxide

What this question tests

This question assesses your ability to represent covalent bonding using dot and cross diagrams, recall neutralisation word equations, apply the Law of Conservation of Mass, read scientific instruments accurately, and identify ions present in alkalis.

Part (02.1)

Covalent Bonding in HCl

Completing a dot and cross diagram

💡 Key Knowledge

Hydrogen (H) needs 2 electrons to fill its outer shell.
Chlorine (Cl) needs 8 electrons to fill its outer shell.
In a covalent bond, atoms share a pair of electrons.

🧠 Exam Technique

The question asks for outer shells only. Do not draw the inner shells of Chlorine, or you may lose marks for cluttering the diagram.

✅ Correct Answer

Diagram Description:

One shared pair of electrons (one dot and one cross) in the overlapping section between H and Cl circles.
6 more crosses (non-bonding electrons) drawn on the outer shell of the Chlorine atom.

1 mark for the shared pair | 1 mark for the 6 non-bonding electrons on Cl.

❌ Common Errors

Students often forget to draw the "lone pairs" (the 6 electrons not involved in bonding) on the Chlorine atom. Without these, Chlorine does not have a full outer shell.

Part (02.2)

Neutralisation Equations

✅ Correct Answer

hydrochloric acid + sodium hydroxide → sodium chloride + water

1 mark for "sodium chloride". (Accept NaCl)

💡 Key Knowledge

This is a Neutralisation reaction. The general rule is:

Acid + Alkali → Salt + Water

The first part of the salt name comes from the metal (Sodium).
The second part comes from the acid (Hydrochloric → Chloride).

Part (02.3)

Conservation of Mass

📐 Calculation Steps

Find total mass of reactants: 3.65g (HCl) + 4.00g (NaOH) = 7.65g
Apply the law: Total mass of reactants = Total mass of products.
Subtract known product: 7.65g (Total) - 1.80g (Water) = 5.85g

✅ Correct Answer

Mass = 5.85 g

1 mark for the correct value.

Parts (02.4) & (02.5)

Temperature and Energy

🧠 Reading the Scale (02.4)

Look closely at Figure 5. There are 5 small divisions between 17 and 18. This means each small line represents 0.2°C.

The liquid level is 3 lines above 17.

17 + (3 × 0.2) = 17.6°C

💡 Reaction Types (02.5)

If the temperature increases, energy is being released to the surroundings.

This is an Exothermic reaction.

✅ Correct Answers

02.4 Temperature: 17.6 °C

02.5 Reaction type: Exothermic (Neutralisation is also accepted)

Part (02.6)

Ions in Alkalis

💡 Key Knowledge

Sodium hydroxide is an ionic compound with the formula NaOH. When it dissolves in water, it splits into its constituent ions:

Na⁺ (Sodium ion)
OH⁻ (Hydroxide ion) - This ion is what makes a solution alkaline!

✅ Correct Answer

Tick the boxes for: Na⁺ and OH⁻

1 mark for each correct ion.

❌ Common Errors

Do not confuse H⁺ (Hydrogen ion) with OH⁻. H⁺ ions are found in acids, while OH⁻ ions are found in alkalis.

Topics

Chemistry · C2: Bonding, Structure and the Properties of Matter · C3: Quantitative Chemistry · C4: Chemical Changes · C5: Energy Changes

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.