What is the pH of a solution prepared by dissolving 0.140 g of potassium hydroxide in sufficient pure water to prepare 250.0 ml of solution?
A)2.000
B)6.000
C)10.000
D)12.000
E)14.000

Question

Quizplus · Accepted Answer

Potassium hydroxide (KOH) is a strong base, so it dissociates completely in water. The molar mass of KOH is approximately 56.11 g/mol. Thus, 0.140 g of KOH is 0.140 g / 56.11 g/mol = 0.002495 mol. When dissolved in 250.0 ml (or 0.250 L) of solution, the concentration of KOH (and thus OH- ions) is 0.002495 mol / 0.250 L = 0.00998 M. The pOH of the solution is -log(0.00998) ≈ 2. Therefore, the pH is 14 - pOH = 14 - 2 = 12.

What Is the PH of a Solution Prepared by Dissolving