Ice and Margaritas
Name: Matt K.
Date: Thursday, June 06, 2002
Why does ice form on the outside of a margarita
glass?.... is the drink on the inside of the glass less than 0 C, and if
so, how is that?
The drink on the inside is just as cold, perhaps a little colder, than the
ice on the outside. The liquid on the inside, however, is not water. The
temperature 0 C is the freezing temperature for water at standard
atmospheric pressure, but there is nothing else special about 0 C. Every
liquid has its own freezing temperature. Alcohol requires a temperature
much less than 0 C in order to freeze. Since a margarita has alcohol as one
of its main chemicals, a margarita freezes at a lower temperature than water.
The ice on the outside of the glass is water from the surrounding air.
Dr. Ken Mellendorf
Illinois Central College
Margaritas are slush drinks, in which liquid (drink) and solid (ice) are in
equilibrium. Basically, because the drink contains more stuff than just
water, its freezing point is below the freezing point of water. When
crushed ice is placed in the Margarita, it melts, absorbing heat. This
lowers the temperature. When the temperature of the drink equals the
freezing point of the mixture, no more ice melts. This temperature,
however, will be below the freezing temperature of pure water, so water from
the atmosphere that condenses on the outside of the glass will freeze.
Exactly the same process occurs when a salt/ice mixture is used to freeze
ice cream. The freezing point of saltwater is below that of pure water, so
ice absorbs heat and melts until the temperature of the mixture is low
enough to keep any more ice from melting.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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Update: June 2012