The Witch's Potion

This demonstration shows that phenolphthalein is a chemical that displays different colors depending on the acidity or basicity of the environment.

Materials
2-500 mL beaker (or 2 large, clear containers)
4-250 mL beakers (or 4 tall glasses)
phenolphthalein (or Exlax or Alophen pill)
ammonia clear (or household ammonia)
acetic acid (or vinegar)
water

Procedure
1. Prepare 4 glasses and label them:
In #1 and #3 put 5 drops of phenolphthalein
In #2 and #4 put 5 drops of ammonia
If you prepare these ahead of time, then be sure to stack them, one inside the other, with an empty one inside the top one. This prevents your drops from evaporating.
2. In one of the large containers put 20 drops of vinegar. Fill the other large container with water.
3. Choose 5 volunteers, 4 witches and someone to read the poem.

Read :
"Four witches made quite a commotion.
When I invited them to create a potion.
Into four glasses went the magic brew,"
STOP

Fill each glass 1/4 - 1/2 full with water. All will be clear.

Read:
"And into a rage the first witch flew:
She shrieked, 'There's no magic in this drink
To cast a spell, it must be pink!'
The second witch laughed, 'The pink is here.
Pour your brew in--the color will appear!'"
STOP

Have Witch #1 pour her water into the glass of Witch #2. The phenolphthalein will react with the ammonia and turn bright pink,indicating the presence of a base.

Read:
"The third witch shrieked, 'We need more!'
And gave her brew to Witch number Four."
STOP

Have Witch #3 pour her water into the glass of Witch #4. The phenolphthalein will react with the ammonia and turn bright pink, indicating the presence of a base.

Read:
"Now there are two glasses of pink,
But no one asked me what I think!
I'll invoke my powers to make it clear-
'Be Gone Pink!' 'Watch it disappear!!'"
STOP, END

Pour both glasses with the pink solution into the glass container with vinegar. The acid will neutralize the base and the liquid will be clear again.

Teacher's Notes
Phenolphthalein is an indicator that turns pink in the presence of a base (like ammonia) but is colorless in an acid (like vinegar). Because the phenolphthalein solution is made with alcohol, it will evaporate easily. You should plan to put the solutions in cups just before the demonstration or "nest" your cups after you prepare them so the alcohol does not evaporate. The vinegar will neutralize the base (ammonia) so the resulting solution will be fairly harmless and can be flushed down the drain for disposal.