Cabbage pH Lab
Background
Red cabbage contains a pigment molecule called flavin. This water-soluble pigment is also found in apple skin, plums, poppies, cornflowers, and grapes. Very acidic solutions will turn anthocyanin a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is impossible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice.
The color of the juice changes in response to changes in its hydrogen ion concentration.
pH 2 4 6 8 12
Color: red purple violet blue-green greenish yellow
KNOW: What do you know about a pH indicator?
Materials
Red cabbage, knife, boiling water, filter paper, large beaker, five 250 mL beakers, lemon juice, vinegar, antacids, baking soda
Procedure
1. Chop the cabbage into small pieces until you have about 1.5 cups.
2. Place the cabbage in a large beaker of boiling water and allow at least ten minutes for the color to leach out of the cabbage.
3. Filter out the plant material to obtain a red-purple-bluish solution.
4. Pour about 50–100 mL of your cabbage juice into five 250 mL beakers.
6. Add various household solutions into the juices to look for a pH color change.
7. Record your observations.
8. Test the solutions with pH papers, and record you observations.
Data
Solutions / Color / Cabbage pH / Electronic pHCabbage
Lemon
Vinegar
Antacids
Baking Soda
WHAT: What did you learn about pH indicators?
Answer two analysis questions with complete sentences.
1. How does the pH chart from the cabbage juice compare to the pH chart from the litmus paper? Are the results similar or different?
2. Which solution was close to neutral, and why would this be important?
3. Which solutions were basic, and which solutions where acidic?
LEARN: What do you still want to learn about pH indicators?