Calculate pH of a solution prepared by dissolving 0.09 g potassium hydroxide (KOH) to make 500 ml assuming that 7% of its mass is moisture.

General Information:
Potassium hydroxide (KOH) is a strong base. It completely ionizes in solution to produce potassium ions (K⁺) and hydroxyl ions (OH^-). It has a molar mass (molecular weight) equal to 56.11 g/ mole.

Calculations:

Mass of moisture = 0.09 × (7/100) = 0.0063 g
Actual KOH mass = 0.09 - 0.0063 = 0.0837 g
Number of moles = mass/ molar mass = 0.0837 ÷ (56.11 g/ mole) = 0.0015 mole
Volume of solution in liters = 500 ml × (0.001 liter/ ml) = 0.5 liter
Molar concentration = number of moles/ volume = 0.0015 mole / 0.5 liter = 0.003 moles/ liter

[OH^-] = [KOH]
pH = 14 + log (0.003)
pH = 14 - 2.52
pH = 11.48

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