# Explain why sulfur dioxide is classified as an acidic oxide.

> Cambridge International IGCSE Chemistry (0620) — 7.2 Oxides · Explain · 4 marks

> Sulfur dioxide is released into the atmosphere when fossil fuels containing sulfur impurities are burned.

## Mark scheme (4 marks)

1. Sulfur dioxide reacts with water (to form an acid)
2. Forms sulfurous acid / H₂SO₃ (named or formula accepted)
3. Sulfur dioxide reacts with alkalis / bases
4. To form a salt (only) / no water produced in the reaction with a base

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-sulfur-dioxide-is-classified-6c98f51a) · Published by Druglandscape Ltd.