Test Tubes and Boiling Tubes
Test tube and boiling tube sizes, uses, and safe heating techniques for IGCSE Chemistry 0620 practical work.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Description
Test tubes are small, thin-walled glass cylinders closed at one end, used for small-scale reactions and qualitative analysis tests. They are the most frequently used piece of glassware in IGCSE chemistry.
Boiling tubes are larger versions of test tubes, designed to withstand heating of liquids more safely. Their wider diameter allows vapour to escape without forcing the liquid out.
| Feature | Test tube | Boiling tube |
|---|---|---|
| Diameter | ~15 mm | ~25 mm |
| Length | ~150 mm | ~200 mm |
| Typical volume | 10-15 cm3 | 30-50 cm3 |
| Main use | Qualitative tests, mixing small amounts | Heating liquids, larger-scale tests |
Uses in IGCSE Chemistry
- Qualitative analysis: Adding reagents to test for cations, anions, and gases
- Small-scale reactions: Observing colour changes, precipitate formation, gas production
- Heating liquids: Boiling tubes for heating solutions; test tubes for gentle warming
- Collecting small volumes of gas: Inverted over water or with a delivery tube
- Holding solids for heating: Clamped horizontally or at a slight angle with the mouth pointing downward (to prevent condensed water running back and cracking the hot glass)
Safe heating
- Never fill more than one-third full. Overfilling increases the risk of bumping and liquid shooting out.
- Hold with a test tube holder or tongs, not bare hands.
- Angle the tube at about 45 degrees.
- Point the open end away from yourself and others.
- Heat gently by moving the tube back and forth through the flame. Do not hold it still in the hottest part.
- For solids, clamp the tube at a slight downward angle so that any water produced runs away from the hot zone (prevents cracking).
Common errors
Pointing the tube at someone: Hot liquid can be ejected during bumping. This is a safety issue and loses marks in planning questions.
Overheating in one spot: Creates a local hot spot where the liquid boils violently. Move the tube through the flame continuously.
Overfilling: Liquid boils over and is lost. Fill no more than one-third.
Using a test tube when a boiling tube is needed: If the method requires sustained heating of a liquid, the wider boiling tube is safer and more appropriate.
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