Experiment 1 • Experiment 2 & 3 • Experiment 5

Experiment 4
In this experiment you will use red cabbage juice to find out the pH of different common substances and liquids. You can compare the results from this experiment with the results found from the soil samples taken from the five suspects.

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.

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

What is an acid? Most of us our 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 acids include: lemon juice, orange juice and vinegar. Red cabbage juice will turn into a different color when mixed with an acid.

 

What is a base? Strong bases can be just as corrosive and dangerous to handle as strong acids. Some drain cleaners that you use 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. This color is a different color than the color it changed into when mixed with an acid.

 

Help!
Watson could not remember what colors red cabbage juice exhibits when it comes in contact with an acid or a base. You can help him remember by comparing your results with the results he got when he used red cabbage juice to determine the pH of the suspect's soil samples.

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
• some acids like lemon juice and white vinegar
• a neutral pH liquid like tap water
(Tap water is usually 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)
• some small clear cups or glasses


III] Procedure
  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 (about a tablespoon (15 milliliters)). In another glass mix about a tablespoon of water with a teaspoon (5 milliliters) of baking soda. Using tape and a marker, label these glasses base.
  5. Prepare your acids. Pour a small amount (about a teaspoon (5 milliliters)) of lemon juice into a glass. In another glass pour in about a tablespoon (15 milliliters) of white vinegar. Using tape and a marker, label these glasses acid.
  6. In another glass pour in a small amount of tap water (about 2 tablespoons (30 milliliters)). Using tape and a marker, label this glass neutral pH.
  7. Pour about 2 to 3 tablespoons (40 milliliters) of red cabbage juice into each of your labeled glasses. Mix each solution carefully and observe the color changes. Answer the question below.

 
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