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You combine 0.75 moles formate and 0.85 moles formic acid to make a buffer solution. The Ka of formic acid is 1.8x10-4 what is the pH of the solution

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Answer:

pH = 3.68

Explanation:

We can solve this problem by using Henderson-Hasselbach's equation:

  • pH = pKa + log[tex]\frac{[Formate]}{[Formic Acid]}[/tex]
  • Where pKa = -log(Ka)
  • pKa = -log(1.8x10⁻⁴) = 3.74

Assuming we have 1 L of the buffer solution then the molar concentrations of formate and formic acid would be:

  • [Formate] = 0.75 mol / 1 L = 0.75 M
  • [Formic Acid] = 0.85 mol / 1 L = 0.85 M

We now have all required data to calculate the pH:

  • pH = 3.74 + log[tex]\frac{0.75}{0.85}[/tex]
  • pH = 3.68

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