What is the pH of a solution prepared by dissolving 0.0800 mol of a strong monoprotic acid HA in enough water to make 200.0 mL of solution? Assume complete dissociation.
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Correct answer
A. 0.40
Principle or equation
For a strong monoprotic acid, [H+] equals the acid concentration. pH = -log[H+]. Concentration is moles per liter.
Why this answer is correct
Moles of HA = 0.0800 mol. Volume = 200.0 mL = 0.200 L. Concentration = 0.0800 mol / 0.200 L = 0.400 M. Since HA is a strong monoprotic acid, [H+] = 0.400 M. pH = -log(0.400) = 0.398, approximately 0.40.
Example
If 0.0500 mol of HCl is dissolved in 250.0 mL, concentration = 0.0500/0.250 = 0.200 M, pH = -log(0.200) = 0.70.
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