Practice Quiz

IB Biology Exam Prep

Category - Biology

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Red cabbage (Brassica oleracea capitata rubra) can be used as a natural pH indicator, its pigments change color in response to varying pH levels.

Pigments can be extracted from the leaves of red cabbage, and relative pH can be determined by adding drops of a liquid into the pigment, as noted in the following table:

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

What can a student determine about the red cabbage solution as a natural indicator of pH?
  1. It turns pink in the presence of bases
  2. It turns green in the presence of acids
  3. It turns pink in the presence of acids
  4. It is a poor indicator of acids and bases
  5. It is yellow at a neutral pH
Explanation
Answer: C, It turns pink in the presence of acids.

Key Takeaway: The table indicates that red cabbage solution changes colors based on the pH of substances added to it. Adding acids results in a change of color from blue to violet to red and eventually pink whereas adding bases results in a color change from blue to blue-green to greenish-yellow.

Photo: Red cabbage, by Rick Heath
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