A student dissolves 0.035 mol of a strong monoprotic acid HA in enough water to make 700.0 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+] equals the initial acid concentration. pH = -log10[H+]. Concentration = moles / volume in liters.
Why this answer is correct
Volume = 700.0 mL = 0.700 L. [HA] = 0.035 mol / 0.700 L = 0.050 M. Since complete dissociation, [H+] = 0.050 M. pH = -log(0.050) = 1.301 ≈ 1.30.
Example
For 0.010 M HCl, pH = -log(0.010) = 2.00.
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