C2H5COOH⇌ C2H5COOH– + H+
\[K_\mathrm{a} = \frac {[\mathrm{C_2H_5COO^-][\mathrm{H^+}]}}{[\mathrm{C_2H_5COOH}]}\]
| [C2H5COOH] | [C2H5COOH–] | [H+] | ||
| f.r. | \[0,0318\] | \[0\] | \[0\] | M |
| ∆ | \[-10^{-3,19}\] | \[+10^{-3,19}\] | \[+10^{-3,19}\] | M |
| v.j. | \[0,0318 - 10^{-3,19}\] | \[10^{-3,19}\] | \[10^{-3,19}\] | M |
\[\begin{aligned}K_\mathrm{a} &= \frac {10^{-3,19}\mathrm{M} \cdot 10^{-3,19}\mathrm{M}}{(0,0318 - 10^{-3,19})\mathrm{M}} = 0,00001338\mathrm{M} \\ \mathrm{p}K_\mathrm{a} &= -\lg K_\mathrm{a} = -\lg 0,00001338 = 4,87351864 ≈ 4,87\end{aligned}\]
