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Q & A: Cloudy ice cubes

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Most recent answer: 10/22/2007
Q:
why is ice cloudy in the middle?
- Anonymous
A:
If tap water is frozen rapidly, air bubbles can become trapped in the ice. Tap water contains a lot of dissolved air, and air comes out of solution when water freezes -- the air molecules do not fit very well in the orderly pattern the water molecules arrange themselves in when water freezes. If your freezer is really good and you are using a metal ice tray (or a commercial ice maker like those found in motel corridors), the ice is made very rapidly by cooling all sides of the ice cube at the same time. The ice may form first on the outside, and the water will gradually freeze outside-in. The air will come out of solution as the water freezes -- air molecules are pushed out of the ice and into the water that is still liquid. Bubbles will get trapped inside because the surrounding ice keeps them from escaping. They eventually get pushed to the middle and the ice freezes around them. Lots of little bubbles make the ice look cloudy.

There could also be lots of little cracks in the ice too.

If you freeze water very slowly, you may be able to make very very clear ice. The ice in the antarctic ice sheet is very clear.

Tom

(published on 10/22/2007)

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