What is the pH of a solution prepared by dissolving 0.010 mol of a strong monoprotic acid HA in enough water to make 250 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+]. Concentration = moles / volume in liters.
Why this answer is correct
Volume = 250 mL = 0.250 L. [HA] = 0.010 mol / 0.250 L = 0.040 M. Since it is a strong acid, [H+] = 0.040 M. pH = -log(0.040) = 1.40 (since log(0.04) = -1.3979).
Example
For 0.020 mol in 500 mL, concentration = 0.040 M, pH = 1.40.
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