Science Workshop: Ice-Cream In A Bag

Last term, students in the Science Workshop experimented with the effect of sodium chloride (NaCl) – aka rock salt – on cooling ice. Students learnt that by adding rock salt to ice, the mixture becomes significantly colder than just pure ice water. While pure water freezes at 0 degrees Celsius, water mixed with salt will freeze below 0 degrees Celsius. This experiment was conducted in (some may say) the best way possible – through making ice-cream!

By adding a mix of delicious ingredients together in a bag (see resource list below), and using a simple salt/ice mixture to create a freezer like effect around the bag, students were able to finish off their term with a mouth-watering treat. Hopefully learning some “cool” science in the process!

Ice-cream in a bag experiment

Resources:

  • Measuring spoons and cups
  • Sugar
  • Milk 
  • Cream
  • Vanilla extract
  • Salt
  • Ice cubes
  • Small, sealable bags
  • Large sealable bags

 

Methodology:

  1. In each small sealable bag, place one tablespoon of sugar, ½ cup of half-and-half (or milk or heavy whipping cream), and ¼ teaspoon of vanilla extract. Seal both bags well. 
  2. Add four cups of ice cubes to one of the large, gallon-sized bags. Then add ½ cup of salt to the bag.
  3. Put one of the small bags you prepared into the large bag with the ice cubes. Be sure both bags are sealed shut.
  4. Put on oven mitts or wrap the bag in a small towel and then shake the bag for at least five minutes. Feel the smaller bag every couple of minutes while you shake it, and take a peek at it.
  5. Now do it again, this time with NO salt. What is the difference?

 

Experiment sourced from: https://www.sciencebuddies.org/stem-activities/ice-cream-bag