What is the pH of a solution prepared by dissolving 0.025 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. 1.30
Principle or equation
For a strong monoprotic acid, complete dissociation means [H+] equals the acid concentration. pH = -log10[H+]. Concentration is moles divided by volume in liters.
Why this answer is correct
Moles of HA = 0.025 mol. Volume = 500.0 mL = 0.5000 L. [H+] = 0.025 mol / 0.5000 L = 0.050 M. pH = -log(0.050) = 1.3010, which rounds to 1.30.
Example
If 0.010 mol of HCl is dissolved in 250 mL, [H+] = 0.010/0.250 = 0.040 M, pH = -log(0.040) = 1.40.
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