Thursday, February 28, 2013

The Science of Ice

In Matthew Kirby's Icefall, there is an abundance of ice. It become almost a character, sealing the fjord, groaning and growing, and it certainly plays a tremendous role in the climax of the book. And there's no shortage of ice in Mr. Popper's Penguins either! Let's take a look at ice from a scientist's perspective and explore some of its proprerties. This is a double experiment since it fits with two of our books, and it will show four different properties of ice. Bonus!

Experiment 1:

Ice Property #1: Ice is less dense than water.

Ice Property #2: Ice can preserve things.

We'll test both of these at the same time. First, take some fruit and separate it into two samples. Half of the fruit will be frozen and the other half will be left in the air. Which one do you think will stay more fresh?

Take half of the fruit and put it in a clear, plastic container. Add water to the container until all of the fruit is covered, but be sure that the container isn't full! The ice will need room to expand. Fill a tall water bottle about 2/3 full, then mark the water level on the side of the container with a marker or piece of tape. Predict where the water level will be after it has frozen to ice, then mark your prediction.

Put your fruit container and water bottle in the freezer (and let the other fruit sit out at room temperature) for about 24 hours. Then take your containers out of the freezer and mark the actual level of the ice in the water bottle. How close was your prediction? Leave the fruit container at room temperature and allow the ice to melt. (If you're anxious, you can further explore the properties of ice by chipping away at it or finding ways to melt it faster, such as a hair dryer. But be sure to wear safety glasses!)
Once the ice has melted (but before it gets soggy), compare the once-frozen fruit to the fruit that was left at room temperature. The ice preserved the fruit in a couple of ways. Fruit spoils because of chemical reactions that take place in the air, mostly with oxygen. The ice slows down these chemical reactions by keeping the fruit at a colder temperature where chemical reactions occur much more slowly. It also slows down the process by physically separating the fruit from oxygen.

Experiment 2:

Ice Property #3: The freezing point of water is 32 degrees Fahrenheit (or 0 degrees Celsius). When water reaches this temperature, the water molecules start to lock into place instead of moving around freely.

Ice Property #4: Adding salt lowers the freezing point of water. (So does adding sugar or almost anything else.)

Take a plate of ice cubes and divide it in half. Sprinkle salt on one half and leave the other half salt-free. (You can sprinkle salt on the salty half throughout the experiment.) Watch the ice, and listen too! You'll actually hear the ice cracking as the crystals change their geometry. As the ice melts, you'll see a definite difference in your salted ice cubes. You'll even see little holes where each salt crystal landed. This is because some of the ice at the surface is always melting, but a little is re-freezing too. The salt (or sugar, or whatever happens to be there) keeps the ice from going back into its crystal shape, which keeps it from freezing again. So that spot can't re-freeze, and then the ice just below it melts and can't re-freeze, and get the idea. :) And now you know why they put salt on icy roads in the winter!

For more kid-friendly information and ice experiments, visit here or here. For a fun video that explains why water expands when it freezes, click here. And for a gorgeous ice art project, visit here.

1 comment:

  1. My younger son will get a kick out of these :) Thanks - interesting post!