Be sure that all students are wearing safety goggles and aprons. Direct the students to fill a test tube half full of hot water and then to keep adding Epsom salt crystals with a spoon or spatula to the water until no more crystals will dissolve. They should stir the contents of the test tube with a stirring rod. There must be a layer of undissolved crystals on the bottom of the test tube. Now the students should place the test tube into a jar of ice water and record any observations.
Students can even place the test tube in a freezer, if available, for a few minutes.
Students should notice that more crystals have formed. Finally the students should place the test tube into a jar of hot water and record any observations. Students should notice that the crystals have again dissolved. Ask students to describe what they observed and to answer the above questions. If time permits, have the students add more NH 3 so that they can see that an equilibrium is indeed there.