Friday, September 27, 2013

Calculate pH of 100 ml solution containing 0.1 g potassium hydroxide (KOH).

General information:
KOH is a strong base that accepts a proton from water to produce potassium (K+) and hydroxyl (OH-) ions in solution. The following equation can be used to accurately calculate pH of a strong base solution with concentrations above 10-5 M:

pH = 14 + log [OH-]

Molecular weight (molar mass) of KOH = 56.11 g/ mole

Calculations:
Number of moles of KOH in solution =  0.1 g ÷ 56.11 (g/ mole) = 0.0018 mole
Volume of KOH solution in liters = 100 ml × 0.001 (liter/ ml) = 0.1 liter

Molar concentration of KOH solution = 0.0018 mole ÷ 0.1 liter = 0.018 mole/ liter
pH = 14 + log (0.018) = 14 - 1.75 = 12.25

Related posts:
Online pH calculator
pH of strong base
pH of strong acid

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