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THE EFFECT OF TEMPERATURE ON THE RATE OF DISSOLVING

* PURPOSE

The purpose of this demonstration is to show the effect of temperature on the rate of dissolving of a solid in a liquid.

* DESCRIPTION

This demonstration is appropriate for a middle school or general chemistry course. The rate at which Kool-Aid dissolves in water at three different temperatures is observed.

* TIME REQUIRED

10 minutes

* MATERIALS

Chemicals:
tap water--hot, room temperature, and cold
Kool-Aid--grape or cherry
Equipment:
250-mL beakers*
chemical scoop or spoon
*See Modifications / Substitutions

* HAZARDS

None

* MODIFICATIONS/SUBSTITUTIONS

Clear plastic cups may be substituted for beakers.

* PROCEDURE

  1. Label beakers hot, room temperature, and cold.
  2. Fill each beaker about three-fourths full of water of the appropriate temperature. The volumes should be the same.
  3. Add about one-eighth to one-fourth teaspoon of Kool-Aid to each beaker. The amounts should be the same.
  4. Observe the rates at which the Kool-Aid dissolves.

* DISPOSAL

Pour solutions down drain.

* DISCUSSION

Increasing the temperature increases the rate of dissolving because, at higher temperatures, the solvent molecules are moving more rapidly and therefore come into contact with and solvate the solute molecules more rapidly.

* TIP

This demonstration could be done on an overhead projector. Undissolved material would appear opaque and the depth of color of the solution could be used to observe rate of dissolving.

Submitted by Patti Ruff, Bill Vitori, Irene Walsh, Doug Wilbur, and Joe Don Wilkins


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