Expanding liquids

Class practical

Observing the expansion of water, and comparing the expansion of soda glass and Pyrex.

Apparatus and Materials

For each group of students

• Thermometer -10°C to 110°C
• Tripod
• Aluminium container or water bath
• Bunsen burner
• Soda glass test-tube, 75 mm x 12 mm or similar
• Pyrex glass test-tube, 75 mm x 12 mm or similar
• Bungs with capillary tubing to fit test-tubes
• Test-tube holder
• Bottle of ink (washable)
• Heatproof gloves

Health & Safety and Technical Notes

The tripod and water bath will take time to cool sufficiently before clearing away. If time is short, heat-proof gloves or suitable clothes should be provided.

Read our standard health & safety guidance

The soda and pyrex glass test-tubes should be similar sizes for this experiment to work.

Procedure

1. Heat water in the water bath until the temperature is between 60°C and 80°C. Dip the thermometer into the hot water and watch carefully.
2. Fill a soda glass tube with coloured water (a little ink is suitable for this). Insert the bung so that no air bubbles remain in the tube, and the coloured liquid extends to about 20 to 50 mm above the top of the bung.
3. Grip the test tube in the holder and plunge the tube into hot water. Observe the behaviour of the water level in the tube.
4. Repeat the experiment using a Pyrex test-tube.

Teaching Notes

• Students may observe the initial fall in the thermometer liquid. This fall is due to the glass expanding before the water in the tube. It takes time for energy to be conducted through the glass to the water in the tube.
• When the Pyrex tube is used, the initial dip of the water level is very much less. This is because the expansion of Pyrex is less than soda glass.
• A change in the volume of a liquid or solid indicates a clear change in the average spacing between its molecules.
• Students should discuss the similarities between the thermometer and the test-tube plus capillary tube.

This experiment was safety-tested in March 2006