GCSE-ready- Home
- Lessons
- GCSE & IGCSE Chemistry
- Tests for gases and water
Tests for gases and water
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
Five gases each have a simple test. There are also chemical and physical tests for water.
Gas tests
Testing for water
Chemical test: add the liquid to anhydrous copper(II) sulfate. It turns from white to blue if water is present.
This shows water is present, but not that the water is pure.
This shows water is present, but not that the water is pure.
Is the water pure?
A physical test: pure water boils at 100 °C and freezes at 0 °C (at normal atmospheric pressure).
Impure water boils above 100 °C or melts below 0 °C, often over a range.
Impure water boils above 100 °C or melts below 0 °C, often over a range.
How could you show that a colourless liquid is pure water?
- Add anhydrous copper(II) sulfate: white to blue shows water is present.
- Measure the boiling point: exactly 100 °C shows it is pure.
Answer: It turns anhydrous copper(II) sulfate blue and boils at exactly 100 °C.
Hydrogen: squeaky pop. Oxygen: relights a glowing splint. Carbon dioxide: limewater milky. Ammonia: damp red litmus turns blue. Chlorine: bleaches damp litmus. Water turns anhydrous copper(II) sulfate from white to blue; pure water boils at 100 °C.
The interactive lesson includes the diagrams for this topic.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.