- Acid/base chemistry
- Chemical indicators
- Solubility and temperature
- Several leaves of red cabbage
- One coffee filter
- Large jar
- Glasses or clear cups
- Stovetop or microwave
- Pot or pan
You only need some (not necessarily all) of the following ingredients:
- Baking soda (1–2 tsp)
- Lemon juice (1–2 tsp)
- Vinegar (1–2 tsp)
- Ammonia (1 oz of household variety—like what you use for cleaning)
- Antacids (1 tablet; Alka-Seltzer® works)
- Cut about 2 cups of cabbage and place it in a blender.
- Boil water in a pot, and then add boiling water to the cabbage in the blender. Turn on the blender and blend for about 10 minutes. The hot water will extract a pigment called an anthocyanin from the red cabbage (along with other components). Recall that solubility tends to increase at higher temperatures. Anthocyanins are molecules that will change color depending on the pH of the solution—this will serve as our indicator.
- Filter the plant material out by pouring the solution through a coffee filter and into a large jar. The liquid you obtain should be red/blue/purple in appearance. The exact color you observe will depend on the pH of the water you are looking at, which may be influenced by factors like the ion concentration in your tap water and the other plant components that remain in the solution.
- Pour the solution into various glasses or clear cups. These will be your individual test “beakers” where you can test the pH of various substances.
- Try adding other substances to your solutions and observe how the color changes as they are added. Note that the amount of solution you add to each glass/cup will influence the amount of each test substance (e.g. lemon juice) you need to add to see a color change. For reference, the list below tells you how the color of your anthocyanin indicator solution should change with pH.