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

Answer 1

Answer: 1 × 10^-8 M.

Reason: pH = −log[H+]. The concentrations give pH values:
- 1×10^-2 → pH 2 (acidic)
- 5×10^-2 → pH ≈ 1.3 (acidic)
- 5×10^-4 → pH ≈ 3.3 (acidic)
- 1×10^-8 → pH 8 (basic)

A blue color with a cabbage indicator corresponds to a basic pH (around 8), so 1×10^-8 M is the possible [H+].