Lesson 5: Ice Cream in a Bag
Lesson 5: Ice Cream In a Bag
Category: Science
Have you ever made ice cream? It can be a lot of fun, and you end up with a yummy frozen treat! There is actually 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 turn 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? In this science activity, you will make your own ice cream in a bag and explore the best way to chill the ingredients to make them become a creamy delicious treat!
Materials:
Measuring spoons
Measuring cup
Sugar
Half-and-half. Alternatively, milk or heavy whipping cream may be used.
Vanilla extract
Salt. Different types of salts, such as table salt or rock salt, will all work, but may give slightly different results.
Ice cubes (8 C)
Small, sealable bags, such as pint-sized or sandwich-sized Ziplocs (2)
Gallon-sized sealable bags (2)
Oven mitts or a small towel
Timer or clock
Directions:
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.
Add four cups of ice cubes to one of the large, gallon-sized bags. Then add ½ cup of salt to the bag.
Put one of the small bags you prepared into the large bag with the ice cubes. Be sure both bags are sealed shut.
Put on oven mitts or wrap the bag in a small towel and then shake the bag for five minutes. Feel the smaller bag every couple of minutes while you shake it, and take a peek at it.
Now add four cups of ice cubes to the other large, gallon-sized bag, but this time do not add any salt to it. What do you think will happen without using salt?
Put the other small bag you prepared into this large bag. Be sure both bags are sealed.
Put on oven mitts or wrap the bag in a small towel and then shake the bag for five minutes, as you did before. Again, feel the smaller bag every couple of minutes while you shake it, and take a peek at it.
Repeat as necessary until ice cream has solidified. Enjoy!
What Happened?
You should have seen that the ice cubes in the large bag with salt melted much more, and felt much colder than the ice cubes in the large bag without salt. Because it was cold enough (several degrees below freezing), the ice cube bag with salt should have been able to cool the ingredients enough to harden them and turn them into ice cream. In contrast, the ice cube bag without salt was not cold enough to do this and the ingredients should have remained fluid.
Do not worry, the second bag is not wasted — you can go back and turn the still liquid ingredients into ice cream! Simply put the small bag in the large bag that had ice cubes and salt and shake them for another five minutes.
If you have ever made ice cream with an old-fashioned hand-crank machine, you probably packed a mixture of ice and rock salt around the container holding the cream. The salt allows the ice and salt mixture to get colder than pure water ice. This extra-cold mixture of salt and ice is able to freeze the ingredients in the ice cream machine (and in the bags you used in this activity) and turn them into ice cream. (This is the same process that goes on when icy roads have salt spread on them to melt the ice.) While pure water freezes at 0 degrees Celsius (32 degrees Fahrenheit), water mixed with salt will freeze below 0 degrees Celsius.
*Adapted from sciencebuddies.org
