Potassium hydrogen phthalate (molar mass = 204.2 g/mol)is one of the most commonly used acids for standardizing solutions containing bases.KHP is a monoprotic weak acid with K_a = 3.91 × 10^-6.Calculate the pH of the solution that results when 0.50 g of KHP is dissolved in enough water to produce 25.0 mL of solution.

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Quizplus · Accepted Answer

To find the pH, first calculate the molarity of KHP: 0.50 g / 204.2 g/mol = 0.00245 mol. In 25.0 mL (0.025 L), the molarity is 0.00245 mol / 0.025 L = 0.098 M. For a weak acid, [H⁺] = √(Ka × [HA]) = √(3.91 × 10⁻⁶ × 0.098) = 6.18 × 10⁻⁴ M. The pH is -log(6.18 × 10⁻⁴) ≈ 3.21.

Potassium Hydrogen Phthalate (Molar Mass = 204