Supersaturation

Purpose:

Some chemicals can become supersaturated fairly easily. This means that the solvent is holding more solute than is expected at that temperature. Usually the solvent is water and the solute is a solid. If you disturb a supersaturated solution by shaking the container or dropping something in it a precipitate will quickly form and the excess solute will come out of solution.

Materials:

• small flask

  hot plate

  tongs

  ceramic tile

  sodium acetate trihydrate crystals

Procedure:

1. Heat the flask with the crystals until they are liquified.

   Allow the liquid to continue heating for a few minutes, but do not let it boil.

   Transfer the flask to the tile using the tongs.

   Allow the liquid to cool undisturbed on the tile with a stopper just resting on top of the flask. Do not push the stopper in.

   When the temperature of the liquid is almost room temperature drop a sodium acetate trihydrate crystal into the liquid and observe what happens.

   Take the temperature again after crystalization.

Discussion:

What happens to the temperature after crystalization? How can you find the difference between unsaturated, saturated, and supersaturated solutions?

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