c) Phản ứng :         $C{H}_3\text{COOH\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}+\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}NaOH\to C{H}_{3}COONa+H_{2}O$

Ban đầu:                2.10^-3                     1.10^-3                                        (mol)

Phản ứng:              1.10^-3                               0                  1.10^-3                     (mol)

Sau phản ứng:        1.10^-3                                         1.10^-3                               (mol)

Nồng độ:               0,05                                           0,05                       (mol/L)

Xét cân bằng hóa học sau:

                    $C{H}_{3}COOH\rightleftharpoons C{H}_3{\text{COO}}^{-}+H^{+}K=1,{8.10}^{-5}$

Ban đầu:      0,05            0,05            0                  (mol/L)

Cân bằng:    0,05 - x       0,05 + x       x                  (mol/L)

                    $K=\frac{x.(0,05+x)}{0,05-x}=1,{8.10}^{-5}\Rightarrow x=1,{798.10}^{-5}\Rightarrow pH=4,7$.