# pH Larutan Asam

## Konsep Dasar

Karena zat asam menambah ion $$\ce{H+}$$ pada larutan, maka pH larutan asam dihitung dari konsentrasi ion $$\ce{H+}$$.

$$\ce{pH = - \log [H+]}$$

Asam kuat

$$\ce{[H+]} = \text{a} \:.\: \text{M}$$

$$\text{a}$$ = jumlah ion $$\ce{H+}$$

$$\text{M}$$ = konsentrasi larutan

$$\ce{HCl, HBr, HI, HClO3, HClO4, HNO3, H2SO4}$$

Larutan asam kuat mengalami ionisasi 100%

Asam lemah

$$\ce{[H+]} = \sqrt{\text{Ka} \:.\: \text{M}}$$

$$\ce{[H+]} = \alpha \:.\: \text{M}$$

$$\text{Ka}$$ = tetapan kesetimbangan asam

$$\alpha$$ = derajat ionisasi larutan

$$\text{M}$$ = konsentrasi larutan

semua asam lain yang tidak tergolong asam kuat

Larutan asam lemah mengalami ionisasi sebagian

#### Tetapan Kesetimbangan Asam (Ka)

$$\ce{HA (aq) + H2O(l) <=> H3O+ (aq) + A- (aq)}$$

Tetapan kesetimbangan:

\begin{equation*} \begin{split} \text{Kc} & = \dfrac {[\ce{H3O+}] \:.\: [\ce{A-}]}{[\ce{HA}] \:.\: [\ce{H2O}]} \\\\ \text{Kc} \:.\: [\ce{H2O}] & = \dfrac {[\ce{H3O+}] \:.\: [\ce{A-}]}{[\ce{HA}]} \\\\ \text{Ka} & = \dfrac {[\ce{H3O+}] \:.\: [\ce{A-}]}{[\ce{HA}]} \\\\ \text{Ka} & = \dfrac {[\ce{H+}] \:.\: [\ce{A-}]}{[\ce{HA}]} \end{split} \end{equation*}

Keterangan:

• $$\text{Ka} = \text{Kc} \:.\: [\ce{H2O}]$$
• Konsentrasi $$\ce{H2O}$$ relatif konstan/tidak berubah banyak.
• $$\ce{[H3O+] = [H+]}$$