The Science of Ice Cream

Learn about endothermic reactions by making ice cream!

Not only is ice cream a tasty treat, but it can teach us a lot about science!  In this lesson, learn about the science of making ice cream in your own home!

Here’s what you’ll need:

  1. 4 ounces of whole milk
  2. 4 ounces of heavy cream
  3. ¼ teaspoon of vanilla extract
  4. 4 teaspoons of sugar
  5. Lots of ice
  6. At least ½ cup of rock salt (we substituted pink Himalayan sea salt)
  7. Quart-size freezer bag
  8. Gallon-size freezer bag

Instructions:

Start by putting the milk, cream, vanilla, and sugar in the quart-size freezer bag.   Make sure you close the bag securely so it doesn’t spill.  Then, in the gallon-size freezer bag, layer the ice and salt, making sure that the salt is evenly distributed across the ice.  Fill the bag at least ½ the way up– initially, we did not add enough ice in the bag, and needed to add more later.  Place the quart bag inside the gallon bag, and carefully close the gallon bag.  Rock the bags back and forth by gripping the top of the gallon bag and moving your hands up and down like you’re steering a car (see video).  Do this for six to eight minutes depending on how hard you want your ice cream.  We rocked our ice cream back and forth for eight minutes and had to wait for it to thaw a little.  Open the bag and enjoy!

So what’s happening??

Well, the salt causes the ice to melt in the gallon bag by lowering the ice’s freezing point.  Essentially, the salt prevents the water from staying frozen because the ice now needs lower temperatures to stay in its solid form.  A similar process occurs when we sprinkle salt outside after a snow storm to make roads and sidewalks less slippery.

In order to melt, however, the ice needs energy, in this case, thermal energy, or heat.  Since melting is an endothermic reaction, which just means that heat is absorbed to start the reaction, the ice needs to take energy from its surroundings– in this case, from the contents of the quart-size bag.  When the ice absorbs the heat from the mixture in the quart-size bag, it causes said mixture to freeze into a delicious treat!

(Ingredients and instructions courtesy of https://sciencebob.com/easy-to-make-ice-cream-in-a-plastic-bag/)

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