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why is ice cloudy in the middle?
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.
(republished on 07/25/06)
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