Kitchen Chemistry Experiment 29
The Witches' Potion

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

Materials	Substitutions
2-500 mL beaker	2 large, clear containers
4-250 mL beakers	4 tall glasses
phenolphthalein
ammonia clear	household ammonia
acetic acid	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.
4. 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.
5. 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.
6. 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!!'" 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.