Here’s how you can make a tasty sorbet in five minutes while learning about the effect of freezing point depression with ice and salt.
C(9) found the experiment in our Science Experiments book. We had all the supplies so we were ready for some spontaneous learning fun!
What You Need
- Orange juice (or other juice)
- Crushed ice (or snow)
- Salt (about 4 tablespoons)
- 2 ziplock bags, one larger than the other
- warm gloves
What You Do
1. Pour orange juice into the smaller ziplock bag. Squeeze out excess air and seal.
The orange juice gradually solidifies and turns into sorbet!
The Scientific Explanation
Adding an impurity (salt) to ice lowers its freezing point. The ice wants to melt back to water, but to do this it needs to absorb heat from somewhere – in this case, the orange juice. Heat is transferred from the orange juice to the ice, freezing the orange juice.
This is an endothermic process (heat is absorbed).
For a detailed molecular explanation of why salt melts ice, see this article.
What We Might Try Next Time
We ended up with a very healthy snack, but for a treat we might make a sweeter sorbet by adding sugar. (Here are the ingredients for a simple lemon sorbet, and a whole list of delicious sorbets here – courgette (zucchini) sorbet looks interesting!) We might even try making ice cream in a bag.
An “Ice Energy” lesson plan (includes ice cream recipes)