Edexcel IGCSE Chemistry Group 1 (alkali metals) – lithium, sodium and potassium questions

What You Need To Know

Group 1 (alkali metals) – lithium, sodium and potassium questions can test recall, explanation, calculations, practical method, or data handling. For this subtopic, you should be able to:

• 2.1 understand how the similarities in the reactions of these elements with water provide evidence for their recognition as a family of elements
• 2.2 understand how the differences between the reactions of these elements with air and water provide evidence for the trend in reactivity in Group 1
• 2.3 use knowledge of trends in Group 1 to predict the properties of other alkali metals
• 2.4C explain the trend in reactivity in Group 1 in terms of electronic configurations

How To Answer Group 1 (alkali metals) – lithium, sodium and potassium Questions

1. Start by identifying exactly which specification point the question is testing.
2. Use the command word carefully: state and identify need a direct answer, while describe and explain need linked detail.
3. For tables, graphs, diagrams, and practical questions, quote the relevant observation or reading before drawing a conclusion.
4. When a question asks for a calculation, show the key substitution and include units where they are needed.

Example Questions With Worked Explanations

Example 1: Core Knowledge

Question 1

This question is about the reactions of Group 1 metals with water. A teacher adds a piece of sodium to some water containing universal indicator.

The equation for this reaction is

2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

The sodium floats on the surface of the water and the universal indicator changes colour because an alkaline solution is formed.

Give two other observations.

1

2

Final answer

Any two of the following:

• sodium moves on the surface
• sodium turns into a ball / sphere (or melts)
• effervescence / fizzing / bubbles are seen
• the sodium gets smaller / disappears
• a white trail is seen

Mark scheme points

1. M1 sodium moves on the surface
2. M2 sodium turns into a sphere / ball (allow: sodium melts)
3. M3 effervescence (allow: fizzing / bubbles)
4. M4 sodium gets smaller (allow: disappears / dissolves)
5. M5 white trail seen

Explanation

To get full marks, you need two different visible observations from the reaction.

Do not repeat what the question has already told you: that sodium floats and that the indicator changes colour because an alkaline solution is formed.

• The sodium moves on the surface.
• It may form a small ball / sphere because the reaction gives out heat and the sodium melts.
• Effervescence means bubbles / fizzing are seen as hydrogen gas is produced.
• The sodium gets smaller as it is used up in the reaction.
• A white trail may be seen behind the sodium.

Any two separate observations from this list would score the 2 marks.

Common mistakes

• Repeating that the sodium floats or that the indicator changes colour; these are already given, so they do not earn the marks here.
• Giving the same idea twice, such as fizzing and bubbles; that only counts as one observation.
• Writing the products or the word equation instead of actual observations.
• Saying there is a flame; this is not credited for this question.

Example 2: Using Data and Practical Skills

Question 2

This question is about the alkali metals.

A teacher demonstrates the reaction between sodium and water.

The teacher fills a trough with water and then adds a piece of sodium.

Lithium, sodium and potassium react in a similar way when added to water. The table shows the atomic radius of a lithium atom, a sodium atom and a potassium atom.

Atom	Atomic radius in cm
lithium	1.82 × 10−12
sodium	2.27 × 10−12
potassium	2.80 × 10−12

Deduce the relationship between the atomic radius and the reactivity of the metals.

Final answer

As the atomic radius increases, the metals become more reactive.

Mark scheme points

1. M1 States that as atomic radius increases, the metals get more reactive.

Explanation

Use the values in the table:

• lithium: 1.82 × 10⁻¹² cm
• sodium: 2.27 × 10⁻¹² cm
• potassium: 2.80 × 10⁻¹² cm

The atomic radius increases from lithium to sodium to potassium. These metals also become more reactive down Group 1, so the relationship is:

larger atomic radius = greater reactivity.

For full marks, write the trend directly and clearly in one sentence.

Common mistakes

• Reversing the trend and saying the metals become more reactive as atomic radius decreases.
• Only describing the radius trend without linking it to reactivity.
• Giving an explanation about electrons instead of stating the relationship asked for.
• Examiners reported that the majority got this right, but a few lost the mark by giving the trend the wrong way round, showing weak understanding of the standard form values.

Practise This Subtopic

Build a focused practice set on group 1 (alkali metals) – lithium, sodium and potassium, with questions selected from this part of the Edexcel IGCSE Chemistry specification.