Acids and Bases: Cabbage Juice Indicators

Materials

Safety goggles

Piece of white unlined paper

About ten drops of red cabbage juice (Note: Prepare cabbage juice by chopping a red cabbage into large chunks and boiling for about 15 minutes.  Strain the juice from the cabbage)

Medicine dropper or pipette

Well plate or five small clear dishes (labeled as A1, A2, A3, A4, and A5)

Solutions partially filling wells

Prepare a well plate or 5 shallow dishes of solutions.  Label 5 wells (or 5 dishes) as A1, A2, A3, A4, and A5.  Half-fill as follows

• A1: vinegar
  
• A2: ammonia solution
  
• A3: lemon juice
  
• A4: baking soda solution
  
• A5: Alka-Seltzer solution

To prepare the baking soda solution, stir about 1 teaspoon of baking soda in a cup of water.  For the Alka-Seltzer solution, mix one Alka-Seltzer tablet in a cup of water.

Activity

1. Put on your safety goggles.
2. Place the piece of paper under your well plate so you can see the color changes clearly.
3. Place two drops of cabbage juice into each of wells A1 through A5.
4. Record the colors you see for each of the five substances you tested.

Follow-Up Questions

1. Which of the substances in the well plate are acids?
2. Which of the substances in the well plate are bases?

Answers

1. Vinegar (A1) and lemon juice (A3) are the acids.
2. The bases are ammonia (A2), baking soda (A4), and Alka-Seltzer (A5).

Extension

Cabbage juice is just one indicator of acids and bases. Litmus paper is another indicator used in science labs. Use litmus paper to check your results. What color do you think litmus paper turns in acids? What color do you think it turns in bases?