A student dissolves 0.050 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.
Show the answer and explanation
Correct answer
A. 0.70
Principle or equation
For a strong monoprotic acid, [H+] = concentration of acid. pH = -log[H+].
Why this answer is correct
Concentration = 0.050 mol / 0.250 L = 0.20 M. Since complete dissociation, [H+] = 0.20 M. pH = -log(0.20) ≈ 0.70.
Example
If 0.010 mol in 1 L, [H+] = 0.01 M, pH = 2.00.
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