Witches' Potion Demonstration - Experiment 24

This demonstration shows that phenolphthalein is an acid/base indicator.

Materials Substitutions
2-500 mL beaker 2 large, clear containers
4-250 mL beakers 4 tall glasses
phenolphthalein
3 M ammonia clear colorless household ammonia
3 M acetic acid vinegar
water

Procedure

  1. Prepare four 250-mL beakers and label them 1-4.
    • 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, cover them to reduce evaporation.

  2. In one of the large beakers, put 20 drops of vinegar. Fill the other large beaker 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 and colorless).

  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 solutions into the glass container with vinegar. The acid will neutralize the base and the liquid will be colorless again).

Teacher’s Notes
Phenolphthalein is an indicator that turns pink in the presence of a base, but it is colorless in an acid. Because the phenolphthalein solution is made with alcohol, it will evaporate easily. You should plan to put the solutions in beakers just before the demonstration to reduce evaporation.

Disposal
The solutions can be flushed down the sink.