AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2021: Question 4

9 marks · Standard Demand difficulty · Short Answer

Identify Group 1 elements, interpret a melting point graph, balance a chemical equation, calculate relative formula mass, and compare the reactions of sodium and potassium with water.

Practise this question

Question

A multi-part chemistry question about Group 1 elements. It includes a multiple-choice question on the name of Group 1 elements, a bar chart (Figure 5) showing the melting points of Group 1 elements, a chemical equation to balance, a calculation for the relative formula mass of sodium hydroxide, and a final question asking to compare the reactions of sodium and potassium with water, accompanied by a simple diagram (Figure 6) of sodium reacting with water.
Question text

04 Sodium and potassium are Group 1 elements.

04.1 What is the name of Group 1 elements?

[1 mark]

Tick ( ) one box.

Alkali metals

Halogens

Noble gases 13

04.2 Figure 5 represents the melting points of Group 1 elements.

Figure 5

What is the melting point of sodium?

[1 mark]

Melting point of sodium = °C

*0124.*3 Sodium reacts with water to produce sodium hydroxide and hydrogen.

Balance the equation for the reaction.

[1 mark]

Na + 214H O → 2 NaOH + H

04.4 Calculate the relative formula mass (Mr) of sodium hydroxide (NaOH).

Relative atomic masses (Ar): H = 1 O = 16 Na = 23

[2 marks]

Relative formula mass (Mr) =

04.5 Sodium and potassium both react with water.

Figure 6 shows sodium reacting with water.

Figure 6

Compare what is seen when sodium reacts with water and when potassium reacts

with water.

[4 marks]

Mark scheme

Show the mark scheme A table showing the mark scheme for the questions. It provides the correct answers for the multiple-choice, graph reading, balanced equation, and relative formula mass calculation. For the final 4-mark comparison question, it lists indicative content for similarities and differences between sodium and potassium reactions, with a level-based marking criteria.

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 alkali metals 1 AO1

5.1.2.5

04.2 98 (°C) allow a value in the range 97–99 1 AO2

(°C) 5.1.2.5

04.3 2Na + 2H2O → 2NaOH + H2 allow multiples 1 AO2

5.1.2.5

5.4.1.1

04.4 (Mr =) 23 + 16 + 1 1 AO2

5.1.2.5

= 40 1 5.3.1.2

AO /

Question Answers Mark

Spec. Ref.

04.5 Level 2: Scientifically relevant features are identified; the way(s) in 3–4 AO1

which they are similar / different is made clear and (where AO2

appropriate) the magnitude of the similarity / difference is noted.

Level 1: Relevant features are identified and differences noted. 1–2 AO1

No relevant content 0

5.1.2.5

Indicative Content:

Similarities – sodium and potassium both:

• float

• move

• bubble / effervesce / fizz

• melt

• form a ball

• get smaller or disappear

Differences – potassium:

• moves faster 11

• bubbles faster

• reacts faster

• disappears faster

• catches fire

• lilac flame

Total 9

How to answer it

Group 1: The Alkali Metals

What this question tests

This question assesses your knowledge of the Group 1 elements (Alkali Metals). You need to recall their names, interpret trends from graphs, balance chemical equations, calculate relative formula mass (Mᵣ), and compare the reactivity of different metals in the same group.

Part (04.1)

Naming the Group

Correct Answer

Alkali metals

Key Knowledge

  • Group 1: Alkali metals
  • Group 7: Halogens
  • Group 0: Noble gases
Part (04.2)

Interpreting Data

Reading the melting point of Sodium from Figure 5

Correct Answer

98 °C

Note: The mark scheme allows any value between 97–99 °C.

Exam Technique

Look closely at the scale. On the y-axis, there are 5 small squares between 80 and 100. This means each small square represents 4 °C. Sodium is just below the 100 line.

Part (04.3)

Balancing Equations

Sodium + Water → Sodium Hydroxide + Hydrogen

Balanced Equation

2 Na + 2 H₂O → 2 NaOH + H₂

How to balance

Look at the right-hand side (RHS) first. There are 2 Sodium (Na) atoms in 2 NaOH . To make it equal, you must put a 2 in front of the Na on the left-hand side.

Part (04.4)

Relative Formula Mass (Mᵣ)

Calculate the Mᵣ of NaOH

Step-by-Step Calculation

  1. Identify the Relative Atomic Mass (Aᵣ) for each element: Na = 23, O = 16, H = 1.
  2. Add them together: 23 + 16 + 1
  3. Final Answer: 40

Common Error

Do not use the big balancing number from the previous question (the '2' in 2NaOH) when calculating Mᵣ. Only use the formula itself: NaOH.

Mark Breakdown

1 mark for the correct addition, 1 mark for the final answer of 40.

Part (04.5)

Comparing Reactivity

Sodium vs Potassium reacting with water

The Core Concept

Reactivity increases as you go down Group 1. Potassium is lower than Sodium, so it reacts more vigorously.

Similarities (Both metals...)

  • Float on the surface.
  • Move around on the water.
  • Fizz / effervesce (produce bubbles).
  • Melt into a silver ball.
  • Disappear / get smaller.

Differences (Potassium...)

  • Reacts faster or more vigorously.
  • Produces a lilac flame.
  • Catches fire (Sodium usually doesn't).

Examiner Commentary

To get 4 marks, you must identify both similarities and differences. Use comparative language like "faster" or "more vigorous" rather than just saying "it is fast." The lilac flame is the most important distinguishing feature for Potassium!

Common Misconception

Don't say the metals "dissolve." They are reacting to form a new substance (an alkali), not just dissolving like sugar in tea.

Topics

Chemistry · C1: Atomic Structure and the Periodic Table · C3: Quantitative 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.