This colorful demonstration displays chemical reactions that can be performed with common substances.

Procedure

1. Put 5 drops of phenolphthalein solution into the first beaker. This should be done very shortly before the demonstration, since it will evaporate quickly.
2. Dissolve approximately 5 crystals of magnesium sulfate heptahydrate and approximately 3-5 mL of water in the second beaker.
3. Dissolve 3 pea-sized copper sulfate crystals in approximately 3-5 mL of water in the third beaker.
4. Wrap the cups with aluminum foil to enhance the curiosity of the audience.
5. Pour the ammonia solution into each cup—using a volume that will render the solution invisible to the audience.
6. Lift the aluminum foil masks to reveal the red, white, and blue colors.

Teacher's Notes

The red coloration is due to the presence of an indicator, phenolphthalein, in an ammonia base.

The white coloration is due to a precipitate that forms when MgSO₄ reacts with aqueous NH₃. Mg(OH)₂ is the insoluble white product.

The blue coloration is due to a complex ion that forms when Cu²⁺ ions react with aqueous ammonia. The formula for the complex ion is Cu(NH₃)₄ ²⁺

The phenolphthalein solution should not be placed into the cup or glass until immediately before performing the demonstration. The indicator is a tincture (a solution of the solid in alcohol) and will evaporate rapidly. After it evaporates, the "trick" will not work.

This work by The Science House is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.