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Q.
The $pK_{a}$ of acetic acid and $pK_{b}$ of $NH_{4}OH$ are 4.76 and 4.75, respectively. Calculate the pH of ammonium acetate solution.
NTA AbhyasNTA Abhyas 2022
Solution:
Acetic acid and $NH_{4}OH$ are weak acid $\left(\right.W_{A}\left.\right)$ and weak base $\left(\right.W_{B}\left.\right)$ respectively. When they combine a salt of $W_{A}$ and $W_{B}$ i.e., ammonium acetate is formed. So by using hydrolysis equation for salts of $W_{A}$ and $W_{B}$ ,
$pH=\frac{1}{2}\left(\right.pK_{w}+pK_{a}-pK_{b}\left.\right)$
$= \frac{1}{2} \left(14 + 4.76 - 4.75\right)$
$=7+0.005=7.005$ .