Water expands when it freezes

In this practical, students observe what happens when a bottle is filled with water and allowed to freeze. The water expands as it freezes, which breaks the bottle. This is useful when teaching about the weathering of rocks and freeze-thaw.

This demonstration can be set up in one lesson and left in the freezer until the next. The demonstration itself takes only a few minutes.

Equipment

Apparatus

• Glass bottle with a lid (see note 2 below)
• Plastic zip-lock type bag (see note 3 below)

Chemicals

• Water

Health, safety and technical notes

1. Read our standard health and safety guidance.
2. A thin-walled glass bottle with a screw-top lid is ideal.
3. A thick plastic bag is best as it will need to contain broken glass. The bag needs to be see-through.

Procedure

Lesson 1

1. Fill the bottle as full as you can and attach the lid.
2. Dry the outside of the bottle, place into the plastic bag and seal it.
3. Put into the freezer at least overnight.

Lesson 2

Remove the bag from the freezer and observe the broken bottle.

Teaching notes

This demonstration shows the very unusual property which water has of expanding when it freezes. In the liquid state water molecules can pack more closely together than in the crystal structure of ice. This means the ice is less dense and so takes up more space than the liquid. It might be worth emphasising to the students that this is an unusual property and most substances become more dense as solids.

This property contributes to the physical weathering of rocks. Rocks which absorb water and then freeze can be broken down as the water expands.

The broken bottle can be put back into the freezer and used again later to show to another class.