What would a student observe if vinegar was slowly added to a red cabbage pigment solution already containing sodium hydroxide (NaOH)?
Here is the pigment table for red cabbage once again:
pH 1-2 Pink/Acid
pH 3-4 Dark Red/Acid
pH 5-6 Violet/Acid
pH 7-8 Blue/Neutral-Base
pH 9-10 Blue-Green/Base
pH 11-12 Green-Yellow/Base
Explanation
Answer: E, The solution would turn from blue-green to blue, then to pink.
Key Takeaway: Sodium hydroxide has a pH of around 10, which would change the pigment to a blue-green color. The major component of vinegar is acetic acid, so adding that to the solution containing sodium hydroxide will lower the pH. The color will in turn change from blue-green to blue, and ultimately to pink.
