Clearer Ice Cubes

By

ThriftyFun

Question:

When I take out an ice cube from the freezer, why is part of it white and part of it clear?

Answers:

The ice cube freezes from top to bottom (or the outside to the inside depending upon how cold your freezer is). In either case, air that is dissolved in the water is trapped in the liquid. Finally, as the ice cube continues to freeze the air no longer stay dissolved but cannot get out through the ice, and air bubbles form. That is what you see as white -- air bubbles. Dissolved salts also do a similar thing, but it is much less noticeable than the air.

You can do an experiment to test this. Take two ice trays and fill one with tap water, and the other with boiled water. Put them both in the freezer and let them freeze. See which one forms the clearer ice cubes. Boiling the water, removes most of the air, so it will form clearer ice cubes.

Vince Calder

The less air in the ice the clearer it is.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy

The water you put in the freezer had some air dissolved in it. As the water froze, the air could not stay dissolved in the solid ice. So the ice that froze first (on the outside of the ice cube) was clear, but the ice that froze later (in the center of the ice cube) was mixed with air bubbles.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

Source: http://www.newton.dep.anl.gov/askasci/gen01/gen01168.htm