question_answer 115)

  \[{{K}_{a}}\]for \[C{{H}_{3}}COOH\] is \[1.8\times {{10}^{-5}}\] and \[{{K}_{b}}\] for \[N{{H}_{4}}OH\] is\[1.8\times {{10}^{-5}}\]. The pH of ammonium acetate will be: (a) 7.005                               (b) 4.75                                 (c) 7.0                                    (d) between 6 and 7

Answer:

  (c) Ammonium acetate is salt of weak acid and weak base, its pH after hydrolysis can be calculated as. \[pH=\frac{1}{2}[p{{K}_{w}}+p{{K}_{a}}-p{{K}_{b}}]\]                 \[=\frac{1}{2}[14+p{{K}_{a}}-p{{K}_{b}}]\]                 \[\text{= 7}\,\,\,\,\,\text{since(p}{{\text{K}}_{\text{a}}}\text{= p}{{\text{K}}_{\text{b}}}\text{)}\]