A student prepares a solution by dissolving 0.040 mol of a strong monoprotic acid HA in enough water to make 800 mL of solution. What is the pH of the resulting solution? Assume complete dissociation.
Show the answer and explanation
Correct answer
A. 1.30
Principle or equation
For a strong monoprotic acid, complete dissociation means [H+] equals the acid concentration. pH = -log[H+].
Why this answer is correct
Molarity = 0.040 mol / 0.800 L = 0.050 M. Since HA is strong, [H+] = 0.050 M. pH = -log(0.050) = 1.30.
Example
If 0.020 mol of HCl is dissolved in 500 mL, [H+] = 0.040 M, pH = 1.40.
This published item includes a stored explanation and passed the platform’s publication workflow. It is independent preparation material, not a claim of an official or recalled examination question.