Chemistry - Ionic Equilibrium Question with Solution | TestHub

Let the concentration of potassium acetate is $x$. According to Henderson's equation, $$\begin{array}{l}\mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}+\log \frac{[\mathrm{salt}]}{[\mathrm{acid}]}\\ 4.8=-\log \left(1.8\times 10^{-5}\right)+\log \frac{x\times 50}{20\times 0.1\mathrm{M}}\\ 4.8=4.74+\log 25x\\ \text{ or }\log 25x=0.06\end{array}$$ $$\begin{array}{l}25x=1.148\\ \therefore x=0.045\mathrm{M}\end{array}$$