Re: [問題] 弱酸 + 弱鹼 pH 計算？

看板Chemistry作者flowerkid (Never give up)時間8年前 (2015/12/19 01:15)推噓1(1推 0噓 0→)

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弱酸、弱鹼滴定以NH3(弱鹼) + CH3COOH(弱酸) 為例, 酸鹼中和後產生-> CH3COO- + NH4+ 在水溶液中 [NH4+] -> [NH3] + [H+] [CH3COO-] -> [CH3COOH] + [OH-] Charge balance [H+] + [NH4+] = [CH3COO-] + [OH-] Mass balance [NH4+]' = [NH4+] + [NH3] (註：[NH4+]'為解離前濃度, [NH4+]為解離後濃度) [CH3COO-]' = [CH3COO-] + [CH3COOH] (註：同上) 由Charge balance => [H+] = [CH3COO-] - [NH4+] + [OH-] 由Mass balance => [CH3COO-] = [CH3COO-]' - [CH3COOH] => [NH4+] = [NH4+]' - [NH3] 代入上式 =>[H+] = [CH3COO-]' - [CH3COOH] - [NH4+]' + [NH3] + [OH-] 又[CH3COO-]' = [NH4+]' 代入上式 =>[H+] = [NH3] - [CH3COOH] + [OH-] 又[NH3] = Ka[NH4+]/[H+] [CH3COOH] = [CH3COO-][H+]/Ka' [OH-] = Kw/[H+] 代入上式 =>[H+] = Ka[NH4+]/[H+] - [CH3COO-][H+]/Ka' + Kw/[H+] 解聯立方程式即可求出[H+]。大致上應該是這樣, 如有誤請指正。 ※ 編輯: flowerkid (111.255.136.117), 12/19/2015 01:27:38

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