KS4 Science Club – Making Ice Cream in a Bag

Did you know that there is a lot of interesting chemistry that goes on behind making ice cream? For example, think about how you start out with refrigerated (or room-temperature) ingredients and then need to cool them down to turn them into ice cream. How do the ingredients change during this process? How important do you think it is that they are cooled to a certain temperature?  

Last Monday Y10 chemists made their own ice cream in a bag and explored the best way to chill the ingredients to make them become a creamy delicious treat! To make their ice cream, students added ice cubes to a large freezing bag alongside the magic ingredient: salt! They then poured double cream, sugar and vanilla extract into a small freezing bag.

Next, they inserted the small bag into the large bag and shook it for a while to solidify the mixture. Salt was key in this experiment as it lowers the freezing point of water by a few degrees. This means when salt is added to the ice in the outer bag, the ice (which is at 0°C) is above its freezing point, so starts to melt. Melting needs energy which in this case comes from the milk mixture in the inner bag. Heat energy is absorbed from the milk, making ice crystals form between the tiny fat molecules. 

A huge thank you to the following Y12 scientists for their help: Sana, Roberto and Anuyah.