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Monday, February 27, 2012

Ice Cream in a Bag Science Experiment

After attending one of our local library's "Test Tube Tuesdays," in which children performed a science experiment that allowed them to make ice cream in a bag, we decided to have the children of our Homeschool group try the same experiment.

We set up stations with each ingredient and had the children fill their 1-quart Ziploc bags with the following items:

They then took their 1-gallon Ziploc freezer bags and filled them with:

The children had to take their 1-quart Ziploc bag and put it inside their 1-gallon Ziploc bag and shake it for about 15 minutes.

After all the shaking was done some children were able to eat their ice cream (for those whose experiment worked).

The other children drank vanilla milkshake instead.

This was a fun experiment.  For those whose liquid did not solidify, we believe it was a case of not having enough ice in the bag.

The bags can get pretty cold so if you try this experiment at home, make sure you wear gloves when shaking the bag.

"Now for the SCIENCE part...Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid.  When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice).  When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt.  This makes the ice colder than it was before, which is how your ice cream freezes.  The salt causes the ice to absorb more energy from the environment (becoming colder), so although it lowers the point at which water will re-freeze into ice, you can't add salt to very cold ice and expect it to freeze your ice cream or de-ice a snowy sidewalk (water has to be present).  This is why NaCI isn't used to de-ice sidewalks in areas that are very cold."

UPDATE:  The following ingredient amounts have been changed.  Use 4 cups of ice (instead of 2 and not crushed ice) and 1 cup of sodium chloride (NaCI) as rock salt (instead of 1/2 cup). 

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  1. Yum! We are going to be making ice cream as one of our Astronomy activities :)

  2. Thanks for the detalied instructions. We may just have to do this in our homeschool group as well.

  3. ASliceofHomeschoolPieFebruary 27, 2012 at 6:12 PM

    Becky, make sure you have plenty of ice. :-)

  4. I have made this many times and it is always fun. However, only about 1/3 of the time does it result in harder ice cream. The kids don't mind, they love the ice milk. I have even duct taped the smaller bag, but somehow the salt still leaks in some of them. Thanks for the reminder.


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