Question

Scenario: You are testing two different household solutions with your cabbage indicator, using the color key to the right.

One solution turns blue. A possible hydrogen ion concentration for this solution is:

1 × 10-2 M

5 × 10-2 M

5 × 10-4 M

1 × 10-8 M
A cabbage p H indicator color key. Entries are 0 to 2, bright red; 3 to 4, pink; 5 to 6, purple; 7, dark violet; 8 to 9, blue; 10 to 11, bright green; 12 to 13, lighter green.

Answer 1

Answer: 1 × 10^-8 M.

Reason: Blue corresponds to pH ≈ 8–9. pH = −log[H+], so [H+] ≈ 10^-8–10^-9 M; 1 × 10^-8 M gives pH 8.