What is the pH of a solution prepared by dissolving 0.020 mol of a strong monoprotic acid HA in enough water to make 500.0 mL of solution? Assume complete dissociation.
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Correct answer
A. 1.40
Principle or equation
For a strong monoprotic acid, [H+] = concentration of acid. pH = -log[H+].
Why this answer is correct
Concentration = 0.020 mol / 0.500 L = 0.040 M. Since HA is strong, [H+] = 0.040 M. pH = -log(0.040) = 1.3979 ≈ 1.40.
Example
For 0.010 mol in 0.250 L, concentration = 0.040 M, pH = 1.40.
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