A student prepares a solution by dissolving 0.0250 mol of a strong monoprotic acid HA in enough water to make 250.0 mL of solution. What is the pH of the resulting solution? Assume complete dissociation.
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Correct answer
A. 1.00
Principle or equation
For a strong monoprotic acid, complete dissociation gives [H+] equal to the acid concentration. pH = -log10[H+]. Concentration is moles divided by volume in liters.
Why this answer is correct
Calculate molarity: 0.0250 mol / 0.250 L = 0.100 M. Since HA is strong monoprotic, [H+] = 0.100 M. pH = -log(0.100) = 1.00.
Example
If 0.010 mol of HCl is dissolved in 0.500 L, [H+] = 0.020 M, pH = -log(0.020) ≈ 1.70.
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