Materials
Per student:
- Gallon Size Freezer Bag
- Quart Size Freezer Bag
- ½ Cup of Rock Salt
- ½ Cup of Whole Milk
- 1 Tablespoon of Sugar
- 4 Cups of Ice
- 1 Teaspoon of Vanilla
- Spoon
- Cup or Bowl
- Thermometer
- Optional: Rainbow Sprinkles, Chocolate Syrup, Crushed Cookies
Procedure
- This experiment is a lot of fun and really messy! Find a spot outdoors to do this or surfaces indoors that can easily be cleaned as saltwater gets just about everywhere.
- Have the students place milk, sugar and vanilla into the quart sized freezer bag.
- Have the students place the ice and rock salt into the gallon size freezer bag.
- Seal the quart size bag very tightly (otherwise students will have salty ice cream) and place the smaller quart size bag in the larger gallon size bag with the ice.
- Have the students then tightly seal the gallon size bag and begin to gently flip the bag back and forth to mix the ice and the salt together.
- After about 10 minutes students can see the ice cream start to harden around the edges of the quart sized plastic bag.
- Have the students take the smaller bag out and measure the temperature of the ice water in the bag, the temperature should be well below the normal freezing point of water, about -5 to -10 degrees Celsius.
- Have the students remove the quart size bag and carefully dump the creamy contents into a bowl.
- The students can then happily enjoy the ice cream (and add the favorite toppings if desired) while every one discusses why the temperature of the ice was so far below freezing.
Explanation
Endothermic means that the substances that react are gaining or absorbing energy in order to react. As the salt mixes with the water and endothermic process occurs, which means heat is pulled out of the surroundings to mix the ice and salt. Since heat is pulled from whatever source is near, much of the heat is pulled from the cream and sugar, causing the once liquid milk and sugar to lose energy and become solid ice cream.
Reinforcement Activities
Teach students about mixing processes, phase changes, the activation of chemical reactions and of course entropy with Cenco Physic’s Anti-entropy set. This intriguing apparatus will allow you to unmix food coloring diffused in a liquid.
Show students an example of an exothermic reaction that they can hold in their hands. This hot pack is made of food grade material so that it is safe for all ages, and is see-through so that students can see the chemicals mix or mix the chemicals inside the pack themselves.
