Ionization Constants of Inorganic Acids
This page has acidity tables for monoprotic acids and polyprotic acids.
The ACS Organic Division's Organic Chemistry Data Website has a list of other collections of pKa values.
| Common Name | Formula | Acidity Constant | pKa |
|---|---|---|---|
| perchloric acid | HClO4 | ca. 1010 | ca. -10 |
| hydrogen iodide | HI | ca. 109 | ca. -9 |
| hydrogen bromide | HBr | ca. 109 | ca. -9 |
| hydrogen chloride | HCl | ca. 107 | ca. -7 |
| nitric acid | HNO3 | ca. 200 | ca. -2 |
| thiocyanic acid | HSCN | 70 | -1.85 |
| hydronium ion | H3O+ | 55 | -1.74 |
| chloric acid | HClO3 | 10 | -1.0 |
| iodic acid | HIO3 | 0.18 | 0.75 |
| hypophosphorous acid | H2P(O)OH | 10-2 | 2.0 |
| hydrogen fluoride | HF | 6.6 * 10-4 | 3.2 |
| nitrous acid | HNO2 | 5.0 * 10-4 | 3.3 |
| cyanic acid | HOCN | 3.54 * 10-4 | 3.45 |
| hydrazoic acid | HN3 | 2.37 * 10-5 | 4.63 |
| hypochlorous acid | HOCl | 2.95 * 10-8 | 7.53 |
| hypobromous acid | HOBr | 2.3 * 10-9 | 8.65 |
| hydrocyanic acid | HCN | 5.8 * 10-10 | 9.25 |
| ammonium | NH4+ | 5.8 * 10-10 | 9.25 |
| hypoiodous acid | HOI | 10-10 | 10 |
| hydrogen peroxide | H2O2 | 2.5 * 10-12 | 11.6 |
| water | H2O | 1 * 10-14 | 14 |
| heavy water | D2O | 3.5 * 10-17 | 16.55 |
| ammonia | NH3 | ca. 10-34 | ca. 34 |
Ionization Constants of Inorganic Polyprotic Acids
| Common Name | Formula | Acidity Constant | pKa |
|---|---|---|---|
| sulfuric acid | H2SO4 HSO4-1 |
K1 = 2.4 * 106 K2 = 1.0 * 10-2 |
-6.62 1.99 |
| chromic acid | H2CrO4 HCrO4-1 |
K1 = 3.55 K2 = 3.36 * 10-7 |
-0.55 6.47 |
| sulfurous acid | H2SO3 HSO3-1 |
K1 = 1.71 * 10-2 K2 = 5.98 * 10-8 |
1.77 7.22 |
| phosphoric acid |
H3PO4 H2PO4-1 HPO4-2 |
K1 = 7.1 * 10-3 K2 = 6.2 * 10-8 K3 = 4.6 * 10-13 |
2.15 7.21 12.34 |
| phosphorous acid | H3PO3 H2PO3-1 |
K1 = 1.6 * 10-2 K2 = 6.3 * 10-7 |
1.8 6.2 |
| pyrophosphoric acid |
H4P2O7 H3P2O7-1 H2P2O7-2 HP2O7-3 |
K1 = 3 * 10-2 K2 = 4.4 * 10-3 K3 = 2.5 * 10-7 K4 = 5.6 * 10-10 |
1.52 2.36 6.60 9.25 |
| carbonic acid | H2CO3 HCO3-1 |
K1 = 4.35 * 10-7 K2 = 4.69 * 10-11 |
6.36 10.33 |
| hydrogen sulfide | H2S HS-1 |
K1 = 9 * 10-8 K2 = ca.10-15 |
6.97 ca.15 |
| boric acid |
H3BO3 H2BO3-1 HBO3-2 |
K1 = 7.2 * 10-10 K2 = 1.8 * 10-13 K3 = 1.6 * 10-14 |
9.14 12.7 13.8 |
The ACS Organic Division's Organic Chemistry Data Website has a list of other collections of pKa values.