Experiment 4

pH analysis

In this experiment you will find out which suspect had soil from the scene of the crime on his or her shoes by using cabbage juice as a pH indicator.

Watson observed that the soil from the suspects’ boots when mixed with cabbage juice exhibited three different colors.

  1. Mr. Plover and Mr. Mopster’s samples turned red.
  2. Mr. Grazzbur and Ms. Blodderbum‘s turned a greenish blue.
  3. Ms. Crowler’s didn’t change color at all, but remained purple.

The kids unfortunately spilled the cabbage juice and need you to find out what color the cabbage juice will exhibit when mixed with a base. We already know that the soil from the scene of the crime is basic (a base).

If you want, you can see a video on how to do this experiment near the bottom of this page. However for the best science discovery experience it best to do the experiment first before watching the tutorial.  

I. Hypothesis Cabbage juice will consistently exhibit one color when mixed with an acid, another color when mixed with a base, and another color when mixed with neutral pH liquids.

II. Materials needed

  • 1/3 of a head of red cabbage
  •  5 small clear glasses or cups
  • a bowl of hot water from the tap
  • clear tape and a permanent marker
  • a sieve, or pasta strainer
  • some bases like baking soda and dish soap (don’t use lemon scented)
  • some acids like lemon juice and white vinegar
  • neutral pH liquid like tap water (Tap water is not a perfect neutral pH. However, for this experiment most tap water will work just fine. If you want to be certain that your water has a neutral pH, use distilled water)

III. Procedure
       ( 1 ounce = 2 tablespoons =30 milliliters)

  1. Break up about 1/3 of a head of read cabbage into tiny pieces.
  2. Soak the cabbage pieces in hot water for at least an 2 hours. Best if you leave it overnight.
  3. Separate the cabbage juice from the cabbage by carefully pouring the juice into an empty glass. You may want to use a sieve to keep out any cabbage pieces.
  4. Prepare bases to be tested. Pour a small amount of dish soap in a glass. In another glass mix about 2 ounces (60 milliliters) of water with a tablespoon (15 milliliters) of baking soda. Label these glasses base.
  5. Prepare your acids. Pour a small amount of lemon juice about 2 ounces (60 milliliters) into a glass. In another glass pour about 2 ounces (60 milliliters) of white vinegar. Label these glasses acid.
  6. In another glass pour in a small amount of tap water (about 3 ounces (90 milliliters)). Label this glass neutral pH.
  7. Pour about about 1 ounce (30 milliliters) of red cabbage juice into each of your labeled glasses. Mix each solution carefully and observe the color changes.



Understanding pH

V. What is pH? pH is used to measure whether or not a solution is an acid, a base or neutral. A neutral solution is neither an acid nor a base. Pure water is an example of a neutral liquid.

lemonVI. What is an acid? Most of us are familiar with term acid. For years, Hollywood has shown us some extreme examples of acids. You might have seen a movie in which a bottle of acid drops, breaks and burns a hole in the floor. Indeed, very strong acids can burn and should be handled with care. Some acids are so strong that just smelling them can burn your nose! However, we are surrounded by many other weaker acids, which are safe to handle. Some examples of weak acids include: lemon juice, orange juice and vinegar. Red cabbage juice, which acts as a pH indicator, will turn colors when mixed with an acid.

baking sodaVII. What is a base? Strong bases can be just as corrosive and dangerous to handle as strong acids. Some drain cleaners used to dissolve clogs are strong bases. However, like acids, some bases are weak bases and are safe to handle. Baking soda and dish soap are two bases that are safe to touch. Red cabbage juice will also turn colors when mixed with a base.

From this experiment you should now know what color cabbage juice will turn to when mixed with an acid or a base.


End Experiment 4