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Reviewed CSCA Chemistry question · Easy

What is the pH of a solution prepared by dissolving 0.060 mol of a strong monoprotic acid HA in enough water to make 300.0 mL of solution? Assume complete dissociation.

  1. 0.70
  2. 1.30
  3. 2.00
  4. 0.30
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+]. Concentration = moles / volume in liters.

Why this answer is correct

Volume = 300.0 mL = 0.300 L. [HA] = 0.060 mol / 0.300 L = 0.20 M. Since complete dissociation, [H+] = 0.20 M. pH = -log(0.20) = 0.70.

Example

If 0.010 mol in 0.100 L gives [H+] = 0.10 M, pH = 1.00.

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