Question Detail
Question
The pH of a 0.10 M solution of a weak acid is 2.87. What is the Ka of this acid?
Correct Answer
Option C is the correct answer.
Detailed Explanation
[H⁺] = 10⁻²·⁸⁷ = 1.35 × 10⁻³ M. Ka = [H⁺]²/(C - [H⁺]) = (1.35×10⁻³)²/(0.10 - 0.00135) = 1.82×10⁻⁶ / 0.09865 = 1.85×10⁻⁵ ≈ 1.8×10⁻⁵.
Hint
Use the formula for a weak acid: Ka = [H⁺]²/(initial concentration - [H⁺]).