HL ⇌ H+ + L–
| [HL] | [H+] | [L–] | ||
| f.r. | \[0,010\] | \[0\] | \[0\] | M |
| ∆ | \[-x\] | \[+x\] | \[+x\] | M |
| v.j. | \[0,010 - x\] | \[x\] | \[x\] | M |
\[\begin{aligned}K_\mathrm{a} &= \frac {[\mathrm{H^+}][\mathrm{L^-}]}{[\mathrm{HL}]} \\ 10^{-3,86} &= \frac {x \cdot x}{0,010 - x} \\ 10^{-3,86}(0,010 - x) &= x^2 \\ 10^{-3,86} \cdot 0,010 - 10^{-3,86}x &= x^2 \\ 0 &= x^2 + 10^{-3,86}x - 10^{-3,86} \cdot 0,010\end{aligned}\]
\(pq\)-formeln ger:
\[\begin{aligned}x &= 0,0011079\mathrm{mol} = [\mathrm{H^+}] \\ \mathrm{pH} &= -\lg[\mathrm{H^+}] = -\lg0,0011079 = 2,95549944 ≈ 2,96\end{aligned}\]
