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Reviewed CSCA Chemistry question · Standard

A solution is prepared by dissolving 0.0200 mol of a strong monoprotic acid HA in water to make 500.0 mL of solution. What is the pH of the solution?

  1. 1.40
  2. 1.70
  3. 2.00
  4. 0.70
Show the answer and explanation

Correct answer

A. 1.40

Principle or equation

For a strong monoprotic acid, [H+] equals the acid concentration. pH = -log[H+]. Molarity = moles / volume in liters.

Why this answer is correct

Molarity = 0.0200 mol / 0.500 L = 0.0400 M. pH = -log(0.0400) = 1.3979 ≈ 1.40.

Example

For 0.0100 mol in 250 mL, M = 0.0400 M, pH = 1.40.

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