Kitchen Chemistry
Experiment 13
Red, White, and Blue I
This colorful
demonstration diplays chemical reactions that can be performed
with common substances.
| Materials |
Substitutions |
| phenolphthalein
solution |
none
(Exlax no longer works) |
| aluminum
foil |
|
| magnesium
sulfate heptahydrate |
Epsom
salt |
| ammonia |
household
ammonia, clear |
| 3-250
mL beakers |
3 plastic
cups |
| glass
stirring rod |
plastic
drinking straw |
| copper
sulfate pentahydrate |
Roebic,
Root Killer K-77 |
| water |
|
Procedure
- Prepare
phenolphthalein solution by opening the Exlax pill. Put the white
powder into the glass and add 1 tablespoon of rubbing alcohol.
This solution can be saved in a dropper for future use. Label
it "phenolphthalein."
- Put 5
drops of Exlax (phenolphthalein) solution in the first cup. This
should be done shortly before the demo since it will evaporate
if left for a few minutes.
- Put 5
epsom salt crystals and a little bit of water in the second cup
and three match head-size copper sulfate crystals (crushed) and
some water in the third cup. These should be prepared ahead of
time so the crystals can dissolve completely.
- Wrap
the cups with aluminum foil to enhance the curiosity of the audience.
- Pour
the clear household ammonia into each cup.
- Lift
the aluminum foil mask to reveal the red, white, and blue colors.
Teacher's
Notes
The "red"
reaction is the action of an indicator, phenolphthalein, on a
base, household ammonia. The "white" reaction is a
precipitate between MgSO4 solution and NH4OH solution (ammonia).
Mg(OH)2 is the insoluble white product that results. The "blue"
reaction is a complex ion reaction between CuSO4 solution and
NH4OH (ammonia).
The phenolphthalein
solution should be placed in the cup or glass JUST BEFORE performing
the demonstration. Since the indicator is a tincture, or alcohol
solution, it will evaporate rapidly. After it evaporates, the
"trick" will not work.
