# "Explain" questions — WJEC GCSE Chemistry (Wales)

> 49 questions · chemistry

## How to answer

WHAT + WHY. Every point paired with a because. Structure: X happens because Y. This causes Z because … Assessment Objective: AO2. Every "explain" answer on this spec is marked against exactly this pattern.

## Sample questions

1. [A food scientist is checking the purity of a sample of vanilla flavouring before it is used in a product. She carries ou…](https://www.gradenine.co.uk/q/a-food-scientist-is-checking-the-01163e29)
2. [When water boils, it undergoes a physical change rather than a chemical change. Explain the difference between a physica…](https://www.gradenine.co.uk/q/when-water-boils-it-undergoes-a-030e473d)
3. [Calcium hydroxide solution is used to test for carbon dioxide gas. Explain what is observed when carbon dioxide is bubbl…](https://www.gradenine.co.uk/q/calcium-hydroxide-solution-is-used-to-081866a0)
4. [Propane (C₃H₈) is a hydrocarbon fuel used in camping gas stoves. When propane burns completely in oxygen, carbon dioxide…](https://www.gradenine.co.uk/q/propane-c-h-is-a-hydrocarbon-fuel-1015689b)
5. [A chemist is investigating whether a sample of red food colouring is a pure substance or a mixture. She carries out pape…](https://www.gradenine.co.uk/q/a-chemist-is-investigating-whether-a-18de981c)
6. [A student makes a salt by reacting dilute nitric acid with sodium hydroxide solution. Explain why this reaction produces…](https://www.gradenine.co.uk/q/a-student-makes-a-salt-by-279d6d4a)
7. [Chlorine has two main isotopes: chlorine-35 and chlorine-37. Explain what is meant by the term isotope and describe how …](https://www.gradenine.co.uk/q/chlorine-has-two-main-isotopes-chlorine-35-29cff89f)
8. [Methanol (CH₃OH) and ethanol (C₂H₅OH) are both members of the alcohol homologous series. Explain why ethanol has a highe…](https://www.gradenine.co.uk/q/methanol-ch-oh-and-ethanol-c-h-oh-are-3edd4b64)

## Related

- [WJEC GCSE Chemistry (Wales) revision notes](https://www.gradenine.co.uk/learn/wjec-gcse-chemistry-wales)
- [WJEC GCSE Chemistry (Wales) past papers](https://www.gradenine.co.uk/past-papers/wjec-gcse-chemistry-wales)
- [Practise with AI marking (free)](https://www.gradenine.co.uk/start)