A student dissolves 0.045 mol of a strong monoprotic acid HA in enough water to make 900.0 mL of solution. What is the pH of the resulting solution? Assume complete dissociation.
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Correct answer
A. 1.30
Principle or equation
For a strong monoprotic acid, [H+] = concentration of acid. pH = -log[H+].
Why this answer is correct
Concentration = 0.045 mol / 0.900 L = 0.050 M. Since it's a strong monoprotic acid, [H+] = 0.050 M. pH = -log(0.050) = 1.30.
Example
If 0.010 mol HCl in 1.00 L, [H+] = 0.010 M, pH = 2.00.
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