Chemistry - Ionic Equilibrium Question with Solution | TestHub

For an acidic buffer, $\mathrm{pH}=\mathrm{p}{K}_{\alpha }+\log \frac{[\text{ Salt }]}{[\text{ Acid }]}\dots (i)$ Let the concentration of potassium acetate solution $=x\mathrm{M}$ 20 mL of 0.1 M acetic acid $=20\times 0.1\mathrm{millimol}$ $=2$ millimol 50 mL of $x\mathrm{M}$ potassium acetate $=x\times 50\mathrm{millimol}$ $\begin{array}{rl}& =50x\text{ milimol }\\ \mathrm{pH}& =4.8(Given)\end{array}$ Substitute all value in eq. (i), $\begin{array}{rl}4.8& =-\left(\log 1.8+10^{-5}\right)+\log \frac{50x}{2}\\ \log 25x& =0.06\\ x& =0.04\mathrm{M}\end{array}$