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Name: Matt K.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: Thursday, June 06, 2002


Question:
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?


Replies:
Matt,

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
Physics Instructor
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.
Assistant Director
PG Research Foundation, Darien, Illinois



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