Exactly half of a given volume of formic acid solution is neutralized by the addition of a solution — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

When exactly half of a weak acid is neutralized by a strong base, the concentration of the formed salt equals the concentration of the remaining unreacted weak acid ($[Salt] = [Acid]$). This forms a buffer at its maximum capacity. $pH = pK_a + \log(1) = pK_a$. $pK_a = -\log(2 \times 10^{-4}) = 4 - \log 2 = 4 - 0.30 = 3.70$.