Stop what you are doing, grab your daughter, and try this STEM challenge RIGHT NOW! What better way to learn about physics and chemistry than with a tasty home made ice cream challenge? We had so much fun testing (and tasting!) this out and know you will love it too!
Background
Ever wonder why people put salt on icy roads in the winter? Salt lowers the freezing point of water. Water melts at 32 degrees Fahrenheit so if the road temperature is below that, ice will form. But when you add salt to water, the freezing point can drop down to 0 degrees Fahrenheit meaning that it takes a lower temperature to keep the ice frozen. This means that even if the road temperature is below 32 degrees but you add salt, the ice will start to melt.
Having a hard time visualizing this? Take two ice cubes and sprinkle salt on one of them. Watch what happens and you’ll see how the addition of salt makes the ice melt faster. Both ice cubes will eventually melt at room temperature but the salty ice cube melts faster due to the lower freezing/melting point.
So how can we use this to make ice cream? In order to make cream freeze, the temperature would need to be below 32 degrees Fahrenheit. By adding salt to ice and conducting this experiment at room temperature (~67 degrees), the salt will begin to melt the ice making a solution that is less than 32 degrees allowing the cream to freeze faster.
Now sure, you could put cream into the freezer at 32 degrees and it will eventually freeze but that would take much longer and result in a pretty hard and icy bowl of ice cream. To get that creamy texture we all love about ice cream, we need to introduce air into the cream. This can be done by stirring or shaking. Moving the cream particles around while being exposed to the cold temperature gives it that creamy texture while also allowing for better heat transfer between the salty ice and the cream.
So let’s give it a try! Grab the ingredients and get ready to shake it up for an edible ice cream treat!
Materials
- 1/2 cup heavy cream or half and half
- 1/4 tsp vanilla extract
- 1 TBS sugar
- 1/3 cup kosher salt or table salt
- Ice
- Large ziplock bags
- Small ziplock bags
- Shake It Up Ice Cream Experiment Test Sheet
Methods
- Download and print the Shake It Up Ice Cream Experiment Test Sheet.
- Combine the heavy cream or half and half, vanilla extract, and sugar. Pour this mixture into one of your small ziplock bags. Make one bag for each variable you are testing. We tested ice alone, ice + table salt, and ice + kosher salt.
- Fill the large ziplock bags about 1/2 fill with ice cubes.
- Dump salt into the bags and then place your small cream-filled bag inside it. Make sure both bags are sealed up well.
- Start shaking! We suggest putting on some music and having a dance party while you shake. Make some observations about what is happening inside your bags. How do they look and feel with or without salt? What is happening to the cream inside the small bag?
- After about 5 minutes of shaking, open your bags and scoop the contents of the small bag into a bowl. Do you notice any difference between the bags that contained salt and the one with just ice?
- Add sprinkles, chocolate syrup, or your favorite topping and enjoy your home-made science experiment!
