A student prepares a solution by dissolving 0.030 mol of a strong monoprotic acid HA in enough water to make 750.0 mL of solution. What is the pH of the resulting solution? Assume complete dissociation.
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Correct answer
A. 1.40
Principle or equation
For a strong monoprotic acid, [H+] equals the initial acid concentration. pH = -log[H+].
Why this answer is correct
Calculate molarity: 0.030 mol / 0.750 L = 0.040 M. Since acid is strong and monoprotic, [H+] = 0.040 M. pH = -log(0.040) = 1.3979 ≈ 1.40.
Example
If 0.010 mol HCl is dissolved in 0.500 L, [H+] = 0.020 M, pH = 1.70.
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