✔ 最佳答案
應是:pH = pKa - log([CH3COOH]/[CH3COO⁻])
或者:pH = pKa + log([CH3COO⁻]/[CH3COOH])
證明:
CH3COO⁻ + H2O ⇌ CH3COOH + OH⁻ (Kb)
Kb = [CH3COOH][OH⁻]/[CH3COO⁻]
KaKb = 10⁻¹⁴
KaKb = [H⁺][OH⁻]
Ka = [H⁺][OH⁻] x (1/Kb)
Ka = [H⁺][OH⁻] x [CH3COO⁻]/[CH3COOH][OH⁻]
Ka = [H⁺][CH3COO⁻]/[CH3COOH]
log(Ka) = log([H⁺][CH3COO⁻]/[CH3COOH])
log(Ka) = log[H⁺] + log([CH3COO⁻]/[CH3COOH])
log(Ka) = log[H⁺] + log([CH3COO⁻]/[CH3COOH])
-log[H⁺] = -log(Ka) + log([CH3COO⁻]/[CH3COOH])
pH = -log[H⁺] 及 p(Ka) = -log(Ka)
pH = pKa + log([CH3COO⁻]/[CH3COOH])
pH = pKa + log([CH3COOH]/[CH3COO⁻])⁻¹
pH = pKa - log([CH3COOH]/[CH3COO⁻])