Did you know you can make frost appear on the surface of a metal can using just ice, water and salt? We used the power of science to make our very own Frosty the Snowman!
How to make a Frosty the Snowman
A clean and empty tin can
Crushed ice
Water
Salt
Timer – optional
Fill the tin can about half full with ice and add a little water and a couple of tablespoons of salt.
Wait and watch the frost form.
More ice and salt experiment ideas
Try comparing how fast the frost forms on two cans using ice cubes and crushed ice. Which would you expect to be faster, and why?
Remember that to make this a fair test, you should only change one variable ( ice crushed/not crushed ) and keep everything else ( amount of ice, water, salt, size of can ) the same.
What is frost?
The air around us holds a lot of water which is called water vapour. We can often see this water vapour when it condenses on windows, cars, grass and cobwebs. We call this dew. Cold surfaces generally make the water vapour condense because colder air can’t hold as much water so what it can’t hold turns into droplets on surfaces. If the surface is very cold (below the freezing point of water) the condensed water vapour freezes, this is frost!
Why does salt melt ice?
In our experiment we filled a can with crushed ice and a bit of water. The temperature of the icy water should be around the freezing point of water (zero degrees Celsius). However, for frost to form we need to get it even colder which we do by adding salt. Salt lowers the freezing point of ice, making the ice melt. To do this it draws heat from the surroundings making them even colder. In this case the salt reduces the temperature on the surface of the can to below freezing point which makes the water vapour in the air condense and freeze on the can.
What is freezing point depression?
Freezing point depression is when a substance lowers the freezing point of water. In this case the salt lowers the freezing point of water which makes ice melt.
More investigations you might like:
Great Christmas science investigations
Leave a Reply