# Explain why sodium oxide dissolves in water to form an alkaline solution, whilst sulfur trioxide dissolves in water to form an acidic solution.

> AQA A-Level Chemistry (7405) — 3.2.4 Properties of Period 3 elements and their oxides (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Sodium oxide is a metal oxide / ionic oxide
2. Sodium oxide reacts with water to produce sodium hydroxide (NaOH)
3. Sodium hydroxide dissociates / ionises to release OH⁻ ions, making the solution alkaline
4. Sulfur trioxide is a non-metal oxide / covalent oxide
5. Sulfur trioxide reacts with water to produce sulfuric acid (H₂SO₄), which releases H⁺ ions making the solution acidic

## Key terms

- [alkaline](https://www.gradenine.co.uk/glossary/alkaline)
- [acidic](https://www.gradenine.co.uk/glossary/acidic)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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/explain-why-sodium-oxide-dissolves-in-319be7e6) · Published by Druglandscape Ltd.