Ice Cream in a Bag
Components:
- Milk
- Sugar
- Vanilla extract
- Ice
- Salt
- One Small Ziploc Bag
- One Big Ziploc Bag
- Spoons
Have you guys noticed that before a winter storm they put salt on the road? Do any of you know why they do this? Well, water usually freezes at 32 degrees Fahrenheit, but whenever we add salt to water it freezes at a lower temperature. Salt can decrease the freezing temperature of water to 2 degrees Fahrenheit. One of the reasons we put salt on the road is to decrease the ice on the road, which is really dangerous. But today we will be using this really low temperature to change our ingredients into tasty ice cream!
Can someone tell me the three stages of matter? That’s right! Liquid, solid and gas. Do you know what causes water to freeze? Yes, whenever it gets cold water freezes. Do you think it will be the same for milk? It might freeze but don’t take my word for it, let’s do an experiment to find out. Today we will be making ice cream!
Paul Brooks, a professor in the Department of Anesthesiology, helps a student make ice cream in a bag to show how the addition of salt lowers the freezing point of water.
A student making ice cream in a bag to learn about freezing points.
In order to make ice cream we need to create an environment cold enough to freeze the milk. Here I have ice and salt, can anybody tell me how I can make it really cold in this Ziploc bag? Yes! I will mix the ice and salt to make it really cold! Take some of the ice and place it in your Ziploc, now take some salt and put it in as well. Now shake that bag a to mix it all up. I’m going to be making ice cream too, but I won’t be adding salt to my ice, what do you guys think will happen? What do you think will happen in yours, since you are using salt? Write down your hypothesis, or what you think is going to happen, and then we will see who can make their ingredients cold enough to become delicious ice cream! Now we are giving you a smaller plastic bag with some milk, sugar and vanilla flavor. Place that bag inside the bag with ice and salt. Now shake it!
Laura Yunes, a PhD student in the neuroscience department shows how adding salt to water lowers the freezing point, allowing for ice cream to be made.
Open your bags and take out the smaller bag out. Is it frozen? Why did it freeze? Why didn’t my ice cream made without the salt freeze? Was your hypothesis that you wrote in your notebook before we started correct?
It’s a success! The ice cream tastes great!
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