What happens to water when it freezes? Why do big icebergs float on water? We’ll answer these questions with a simple (and very cold) experiment! Brrrr..
WHAT TO DO
Fill the plastic cup with tap water, then mark the level of the water with the marker. Gently put the cup in the freezer – be careful not to tip any water out of the cup. Leave the cup in the freezer for a few hours or overnight. Once the water has frozen into ice, take the cup out of the freezer. Now check the level of ice: is it higher or lower than the mark you made before?
WHAT DID YOU SEE?
The level of ice is higher than the mark you made before for the water.
Even though you didn’t change the amount of water, the ice is almost overflowing from the cup. This is because water expands when freezing, due to changes in its molecular structure. A water molecule is made of an atom of oxygen and two atoms of hydrogen, strongly bonded together. Different water molecules interact with each other by creating flexible, weak bonds. When water freezes, water molecules create more bonds between each other, and need more space... That’s ice!
Here you can see an illustration of the process:
HOW DO YOU DO IT?
Fill a transparent bowl with water, take the ice out of the plastic cup and place it in the bowl of water. Have a look at what is happening to your piece of ice: does it sink or does it float?
WHAT DO YOU SEE?
The ice is floating in water – it doesn’t sink!
From step 1, we learned that the same amount of water takes up more space when it turns to ice. This means that ice is less dense than water (the same amount of water takes up more space in the form of ice). If you look closer at the ice in your bowl, you will see that most of your ice remains below the surface. The same thing happens to big icebergs floating on seawater in the Arctic and Antarctic! You can only see the tips of the icebergs.
For the most curious of you, here's a really interesting video: