Buffer Solutions

Question

A buffer solution is prepared by mixing 0.1 M CH₃COOH and 0.1 M CH₃COONa. If Ka for acetic acid is 1.8 × 10⁻⁵, the pH of the buffer is:

RankGuru · Accepted Answer

Use the **Henderson-Hasselbalch Equation** for an acidic buffer:
$pH = pK_a + \log\frac{[Salt]}{[Acid]}$
1. Calculate $pK_a$:
$pK_a = -\log(1.8 	imes 10^{-5}) = 5 - \log(1.8) \approx 5 - 0.255 = 4.745$
2. Substitute salt and acid concentrations:
$pH = 4.745 + \log\frac{0.1}{0.1} = 4.745 + \log(1) = 4.745 + 0$
$pH \approx 4.74$
- Note: When $[Salt] = [Acid]$, $pH = pK_a$.

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