A solution is made by dissolving 0.0125 mol of a strong monoprotic acid HA in enough water to produce 250.0 mL of solution. What is the pH of this solution? Assume complete dissociation.
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Correct answer
A. 1.30
Principle or equation
For a strong monoprotic acid, [H+] equals the acid concentration. pH = -log10[H+]. Concentration is moles per liter.
Why this answer is correct
Moles of HA = 0.0125 mol. Volume = 250.0 mL = 0.250 L. [H+] = 0.0125 / 0.250 = 0.0500 M. pH = -log(0.0500) = 1.30.
Example
If 0.020 mol HCl is dissolved in 500 mL, [H+] = 0.040 M, pH = 1.40.
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