Book 9, Question 1
Why Are Ice Cubes Cloudy in the Middle?
Ice cubes are cloudy in the middle because freezing pushes tiny bubbles of air to the center! Water freezes from the outside in, and the air and minerals that were dissolved in the water get squeezed toward the middle. They get trapped there, and that makes the cloudy core.
More fun facts
- Tap water contains a lot of dissolved air.
- Ice can hold much less dissolved air than liquid water, so as water freezes, the extra air gets pushed out.
- In a freezer tray, ice forms on the outside first and freezes inward toward the center.
- The pushed out air has nowhere to escape, so it ends up trapped in the middle as lots of tiny bubbles that make the ice look cloudy.
- Water also carries tiny bits of minerals. The purest water freezes first and pushes those bits toward the center too.
- The perfectly clear ice used for ice sculptures is made by freezing water slowly from one end to the other.
Sources: Illinois, Purdue, livescience.com
Questions kids ask
How can I make clearer ice at home?
Freeze the water slowly from one direction, such as from the top down, so the air can escape instead of getting trapped.