top of page
Search
Writer's pictureKrystyna
Aug 212 min read

Discovery Labs: ICE CREAM IN A BAG

OBJECTIVE:

To demonstrate the process of freezing point depression by making ice cream in a bag using milk, salt, and ice. This experiment will help students understand the concept of lowering the freezing point of water through the addition of salt, allowing the milk to freeze and turn into ice cream without the use of a freezer.


WHAT YOU NEED:

  • Large bag of ice

  • Salt

  • Milk (any kind)

  • 1 tbsp of sugar 

  • 1 tsp of vanilla extract 

  • Resealable plastic bags (1 small and 1 large)

  • Kitchen towel 

  • Ice cream toppings



INSTRUCTIONS:

  1. Pour a cup of milk into a small resealable plastic bag. Add sugar and vanilla extract. Seal tightly.

  2. Half-fill a larger resealable bag with ice and add a generous amount of salt.

  3. Place the sealed milk bag inside the ice-filled bag,  surrounding it by ice.

  4. Seal the larger bag and shake it vigorously, keeping the milk in contact with the ice as much as possible.

  5. Continue for about 5 minutes. Use a towel to protect your hands from the cold.

  6. Check the milk. It should have the consistency of ice cream. If not, continue shaking until the consistency is reached.

  7. Add your favorite ice cream toppings and enjoy!


OBSERVATION:

Watch the transformation of the milk as it turns into ice cream. The ice in the outer bag will start to melt as it absorbs heat from the milk, causing the milk to freeze.


EXPLANATION: Why Does Ice Cream in a Bag Work?

Water normally freezes at 32°F. However, when salt is added, it lowers the freezing point of water (a process known as freezing point depression). The ice in the bag, which is at 32°F, starts to melt because its freezing point has been lowered. As the ice melts, it absorbs heat from the milk, causing the milk to freeze into ice cream. This is why salt is often used to melt ice on roads during cold weather—it lowers the freezing point of the water, causing the ice to melt even if the temperature is below freezing.


CONCLUSION:

This experiment demonstrates how the addition of salt to ice can lower its freezing point, allowing milk to freeze into ice cream. It's an engaging way to explore the principles of freezing point depression and the practical applications of salt.


EXTENSION:

  • Experiment with different flavors and ingredients to create various homemade ice cream recipes.

  • Test how different amounts of salt affect the freezing process.

  • Investigate the effect of placing a mixture of ice and salt in a freezer to see whether it further freezes or remains as a slushy mixture.




Comments

bottom of page