# Candle wax is a mixture of hydrocarbons. When a candle burns completely in a good supply of air, complete combustion occurs. Explain what is meant by the term hydrocarbon, state the products formed during complete combustion of a hydrocarbon, and explain why incomplete combustion is considered more dangerous than complete combustion.

> OCR A-Level Chemistry A (H432) — 4.1 Basic concepts and hydrocarbons · Explain · 5 marks

> Candle wax is a solid mixture of hydrocarbons derived from crude oil. When a candle is lit in a well-ventilated room, the wax undergoes complete combustion. However, in a poorly ventilated room, incomplete combustion can occur.

## Mark scheme (5 marks)

1. A hydrocarbon contains hydrogen and carbon only
2. Complete combustion produces carbon dioxide
3. Complete combustion produces water
4. Incomplete combustion produces carbon monoxide, which is toxic/poisonous
5. Carbon monoxide is dangerous because it reduces the blood's ability to carry oxygen (or: it binds to haemoglobin / it can cause death by poisoning)

## Key terms

- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)
- [complete combustion](https://www.gradenine.co.uk/glossary/complete-combustion)
- [incomplete combustion](https://www.gradenine.co.uk/glossary/incomplete-combustion)

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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/candle-wax-is-a-mixture-of-bed69e78) · Published by Druglandscape Ltd.