Giải bài 11 trang 29- SGK môn Hóa học lớp 11 nâng cao

a.

Gọi x là nồng độ $O{{H}^{-}}$

$\begin{aligned} & C{{H}_{3}}COONa\to C{{H}_{3}}CO{{O}^{-}}+N{{a}^{+}} \\ & 0,1M\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0,1M \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{3}}CO{{O}^{-}}+{{H}_{2}}O\rightleftharpoons C{{H}_{3}}COOH+O{{H}^{-}} \\ & p\text{hân li:}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x} \\ & \text{cân bằng }:\,\,\,\,0,1-\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x} \\ & {{\text{K}}_{b}}=5,{{71.10}^{-10}} \\ & \Leftrightarrow \dfrac{{{x}^{2}}}{0,1-x}=5,{{71.10}^{-10}}\Leftrightarrow x\approx 7,{{55.10}^{-6}} \\ & \Leftrightarrow [O{{H}^{-}}]\approx 7,{{55.10}^{-6}}\Rightarrow [{{H}^{+}}]=\dfrac{{{10}^{-14}}}{[O{{H}^{-}}]}\approx 1,{{3.10}^{-9}} \\ \end{aligned}$

b. 

Gọi x là nồng độ ${{H}_{3}}{{O}^{+}}$

$\begin{aligned} & N{{H}_{4}}Cl\to C{{l}^{-}}+N{{H}_{4}}^{+} \\ & 0,1M\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0,1M \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,N{{H}_{4}}^{+}+{{H}_{2}}O\rightleftharpoons N{{H}_{3}}+{{H}_{3}}{{O}^{+}} \\ & {phân li:}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x} \\ & \text{cân bằng }:\,\,\,\,0,1-\,x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{x} \\ & {{\text{K}}_{a}}=5,{{56.10}^{-10}} \\ & \Leftrightarrow \dfrac{{{x}^{2}}}{0,1-x}=5,{{56.10}^{-10}}\Leftrightarrow x\approx 7,{{5.10}^{-6}} \\ & \Leftrightarrow [{{H}_{3}}{{O}^{+}}]\approx 7,{{5.10}^{-6}}\Rightarrow [{{H}^{+}}]\approx 7,{{5.10}^{-6}} \\ \end{aligned}$

Ghi nhớ:

Khi tính hằng số cân bằng của axit, bazơ trong dung dịch hỗn hợp có muối thì: anion và cation của muối trùng với anion và cation của axit cũng sẽ tính nồng độ cộng vào nồng độ của axit hoặc bazơ phân li.