Science ideas for young children: Keeping your water troughs thawed
Will salt water keep your water troughs thawed?
Have you ever tried the experiment of making ice cream in a zip-top bag with salt and ice? You put salt and ice in a big zip-top bag, and then put a smaller zip-top bag with a liquid ice cream mixture inside it. Ice absorbs thermal energy as it melts and it “pulls” the heat out of the milk mixture, turning it into solid ice cream. The salt lowers the melting point of ice, so more energy needs to be absorbed from the environment.
Do you think this process could work in reverse? Could salt water give off thermal energy as it starts to freeze, rather than ice absorbing thermal energy as it melts?
In several online articles, I saw recommendations about putting sealed water bottles filled with ice water into a water tank (like that used for livestock) to prevent it from freezing. If salt is added directly to water, it will lower the freezing point, but you probably don’t want your animal drinking salt water. Will this still work if the salt doesn’t come into direct contact? How could you test this out?
A simple way to test this would be to put two identical buckets out on a cold night with the same amount of water. Do you think it matters whether the buckets are metal or plastic? Why or why not? Then, put a water bottle filled with salt water in one of the buckets. Check it in the morning to see what happened.
Did one bucket freeze and the other not freeze? If the results weren’t that obvious, were there any differences between the water in the two buckets? Did one have a thicker ice layer than the other?
Some folks have suggested the reason for a difference might not be because of the salt water producing thermal energy, but because the water bottle bobs up and down in the water, and the movement is what prevents the water from freezing. How could you test this?
Another experiment could be to have two identical buckets, one with a salt water filled water bottle, and another bucket with a tap-water filled water bottle. Wait until morning to see if there are differences.
Michigan State University Extension recognizes there are many opportunities for science education that occur in the natural world. This opportunity, around states of matter and thermodynamics, can be conducted by any group working with children, including families, daycares, schools or 4-H clubs. This easy exercise can help develop your child’s inquisitive nature and a love of science. Enjoy the winter, maybe figure out a way to keep your water troughs thawed and enjoy science!