What is the pH of a solution prepared by dissolving 0.050 mol of a strong monoprotic acid HA in enough water to make 250.0 mL of solution? Assume complete dissociation.
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Correct answer
A. 0.70
Principle or equation
For a strong monoprotic acid, complete dissociation gives [H+] equal to the acid concentration. pH = -log[H+]. Concentration = moles / volume in liters.
Why this answer is correct
Moles of HA = 0.050 mol, volume = 0.250 L, so [H+] = 0.050 / 0.250 = 0.20 M. pH = -log(0.20) = 0.70.
Example
If 0.020 mol of strong acid is in 0.100 L, [H+] = 0.20 M, pH = 0.70.
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