試題詳解

H₂CO₃ ⇌ HCO₃^- + H⁺  pK_a = 6.4
H₂PO₄^- ⇌ HPO₄^2- + H⁺  pK_a = 7.2
At pH 6.4, which one of the following is true of the relative amounts of acid and conjugate base present?
(A) [H₂CO₃] ＞ [HCO₃^-] and [H₂PO₄^-] ＞ [HPO₄^2-]
(B) [HCO₃^-] ＞ [H₂CO₃] and [HPO₄^2-] ＞ [H₂PO₄^-]
(C) [H₂CO₃] ＞ [HCO₃^-] and [HPO₄^2-] ＞ [H₂PO₄]
(D) [H₂CO₃] = [HCO₃^-] and [HPO₄^2-] ＞ [H₂PO₄]
(E) [H₂CO₃] = [HCO₃^-] and [H₂PO₄^-] ＞ [HPO₄^2-]