# Strontium (Sr) is a Group 2 metal. When strontium burns in oxygen it forms strontium oxide (SrO). When strontium oxide is added to water, strontium hydroxide solution is formed. Explain what happens during these two reactions, using your knowledge of oxidation, reduction and the reactivity series.

> Edexcel A-Level Chemistry (9CH0) — 4.1 Group 2 metals · Explain · 5 marks

> Strontium (Sr) is a Group 2 metal found below calcium in the periodic table. It reacts vigorously with oxygen when burned, forming strontium oxide (SrO). When strontium oxide is added to water, the solution formed turns universal indicator dark blue.

## Mark scheme (5 marks)

1. When strontium burns in oxygen, strontium is oxidised (gains oxygen / loses electrons)
2. Strontium oxide is a basic/alkaline oxide, so when it dissolves in water it forms a solution with a pH greater than 7 / an alkaline solution
3. Strontium is more reactive than calcium (because it is lower in the reactivity series / lower in Group 2)
4. Reactivity increases down Group 2 because atoms have more electron shells / the outer electron is further from the nucleus / lost more easily
5. Because strontium is more reactive, it burns more vigorously / reacts more readily with oxygen / forms strontium oxide more easily than calcium or magnesium would

## Key terms

- [oxidation](https://www.gradenine.co.uk/glossary/oxidation)
- [reactivity series](https://www.gradenine.co.uk/glossary/reactivity-series)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/strontium-sr-is-a-group-2-a4237d7f) · Published by Druglandscape Ltd.