Chemistry - Ionic Equilibrium Question with Solution | TestHub

Acetic acid and$\mathrm{N}{\mathrm{H}}_4\mathrm{O}\mathrm{H}$are weak acid$\left({\mathrm{W}}_{\mathrm{A}}\right)$and weak base$\left({\mathrm{W}}_{\mathrm{B}}\right)$respectively. When they combine a salt of${\mathrm{W}}_{\mathrm{A}}$and${\mathrm{W}}_{\mathrm{B}}$i.e., ammonium acetate is formed. So by using hydrolysis equation for salts of${\mathrm{W}}_{\mathrm{A}}$and${\mathrm{W}}_{\mathrm{B}}$,
$\mathrm{p}\mathrm{H}=\frac{1}{2}(\mathrm{p}{\mathrm{K}}_{\mathrm{w}}+\mathrm{p}{\mathrm{K}}_{\mathrm{a}}-\mathrm{p}{\mathrm{K}}_{\mathrm{b}})$
$=\frac{1}{2}\left(14+4.76-4.75\right)$
$=7+0.005=7.005$.