Practice Quiz

IB Biology Exam Prep

Category - Biology

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An unknown substance is added to the red cabbage pigment and the color changes from blue to pink. Which of the following substances could NOT be the unknown substance?

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
  1. Baking soda
  2. Acetic acid
  3. Hydrochloric acid
  4. Hydrofluoric acid
  5. Aluminum chloride
Explanation
Answer: A, baking soda. Baking soda would not cause the color to change to pink.

Key Takeaway: Since the color of the pigment changed from blue to pink after the unknown substance is added, the unknown substance must be an acid. Of the choices given, only baking soda is not an acid. It is therefore logical that baking soda was not the agent added to the pigment.
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