Freezing point experiment

In this activity students will experiment with salt to test different freezing points.

When it’s snowy outside learners might see lorries spreading salt on the roads and people shovelling salt onto pavements. This is to melt the ice, to make the roads safer for the traffic and less slippery for pedestrians. In this activity we find out how and why this works!

This freezing point experiment has been created to support the teaching of the primary national curriculum. It's an exciting way to engage children’s sciences and maths skills and get them thinking about liquids, ions, icy surfaces, global warming and more! It can also be conducted at home as a fun family activity.

Activity: Experimenting with salt to test different freezing points

Tools/supplies needed:

• Two jam jars or similar containers
• Something to mark one jar, such as a permanent marker or sticker
• Water
• Table salt (about 2oz)

Follow our step-by-step guide on how to test different freezing points

Adults can help children experiment follow our step-by-step instructions to test different freezing points:

• Learners pour water into both jam jars/containers, until they are about half full.
• In one jar add salt to make a saturated solution. A saturated saltwater solution is made when any further salt added will not dissolve.
• Mark the saltwater solution with the permanent marker or a sticker so the jars don’t get mixed up!
• Place both jam jars in the freezer and close the door.
• Check each hour to see if either jar has frozen. Learners should find that the plain water freezes faster than the saltwater solution.
• When both have frozen remove from the fridge and leave to thaw. They should find the saltwater similarly thaws more quickly than the plain water.

Download our Freezing point experiment worksheet for a printable set of instructions. This worksheet also explores the science behind freezing points.

The engineering context

In addition to reducing the risk of slipping on icy surfaces, the freeze–thaw cycle can cause weathering and the slow deterioration of structural stability in rocks and construction materials, particularly when water has seeped into small cracks and crevices. Engineers have to take this into consideration when designing structures for external use, such as bridges.

Suggested learning outcomes

This activity will teach children how to test the freezing point of water by using salt. Students will also be able to explain how salt’s ions lower water’s freezing point.

Freezing experiment word search

If you’re up for an extra activity, children can try our Freezing experiment word search.

Download our activity sheet and other teaching resources

You can download our step-by-step instructions below as a classroom lesson plan.

All activity sheets and supporting resources are free to download, and all the documents are fully editable, so you can tailor them to your students’ and your schools’ needs.

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