A student dissolves 0.040 mol of a strong monoprotic acid HA in enough water to make 500.0 mL of solution. What is the pH of the resulting solution? Assume complete dissociation.
Show the answer and explanation
Correct answer
B. 1.10
Principle or equation
For a strong monoprotic acid, [H+] equals the acid concentration. pH = -log[H+].
Why this answer is correct
Molarity = 0.040 mol / 0.500 L = 0.080 M. Since HA is strong, [H+] = 0.080 M. pH = -log(0.080) = 1.10.
Example
If 0.020 mol of HCl is in 0.250 L, [H+] = 0.080 M, pH = 1.10.
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