Appendix B: Selected Acid Dissociation Constants at 25°C
| Name | Formula | K a1 | pKa1 | K a2 | pKa2 |
|---|---|---|---|---|---|
| Acetic acid | CH3CO2H | 1.75 × 10−5 | 4.756 | ||
| Arsenic acid | H3AsO4 | 5.5 × 10−3 | 2.26 | 1.7 × 10−7 | 6.76 |
| Benzoic acid | C6H5CO2H | 6.25 × 10−5 | 4.204 | ||
| Boric acid | H3BO3 | 5.4 × 10−10* | 9.27* | >1 × 10−14* | >14* |
| Bromoacetic acid | CH2BrCO2H | 1.3 × 10−3 | 2.90 | ||
| Carbonic acid | H2CO3 | 4.5 × 10−7 | 6.35 | 4.7 × 10−11 | 10.33 |
| Chloroacetic acid | CH2ClCO2H | 1.3 × 10−3 | 2.87 | ||
| Chlorous acid | HClO2 | 1.1 × 10−2 | 1.94 | ||
| Chromic acid | H2CrO4 | 1.8 × 10−1 | 0.74 | 3.2 × 10−7 | 6.49 |
| Citric acid | C6H8O7 | 7.4 × 10−4 | 3.13 | 1.7 × 10−5 | 4.76 |
| Cyanic acid | HCNO | 3.5 × 10−4 | 3.46 | ||
| Dichloroacetic acid | CHCl2CO2H | 4.5 × 10−2 | 1.35 | ||
| Fluoroacetic acid | CH2FCO2H | 2.6 × 10−3 | 2.59 | ||
| Formic acid | CH2O2 | 1.8 × 10−4 | 3.75 | ||
| Hydrazoic acid | HN3 | 2.5 × 10−5 | 4.6 | ||
| Hydrocyanic acid | HCN | 6.2 × 10−10 | 9.21 | ||
| Hydrofluoric acid | HF | 6.3 × 10−4 | 3.20 | ||
| Hydrogen selenide | H2Se | 1.3 × 10−4 | 3.89 | 1.0× 10−11 | 11.0 |
| Hydrogen sulfide | H2S | 8.9 × 10−8 | 7.05 | 1 × 10−19 | 19 |
| Hydrogen telluride | H2Te | 2.5 × 10−3‡ | 2.6‡ | 1 × 10−11 | 11 |
| Hypobromous acid | HBrO | 2.8 × 10−9 | 8.55 | ||
| Hypochlorous acid | HClO | 4.0 × 10−8 | 7.40 | ||
| Hypoiodous acid | HIO | 3.2 × 10−11 | 10.5 | ||
| Iodic acid | HIO3 | 1.7 × 10−1 | 0.78 | ||
| Iodoacetic acid | CH2ICO2H | 6.6 × 10−4 | 3.18 | ||
| Nitrous acid | HNO2 | 5.6 × 10−4 | 3.25 | ||
| Oxalic acid | C2H2O4 | 5.6 × 10−2 | 1.25 | 1.5 × 10−4 | 3.81 |
| Periodic acid | HIO4 | 2.3 × 10−2 | 1.64 | ||
| Phenol | C6H5OH | 1.0 × 10−10 | 9.99 | ||
| Phosphoric acid | H3PO4 | 6.9 × 10−3 | 2.16 | 6.2 × 10−8 | 7.21 |
| Phosphorous acid | H3PO3 | 5.0 × 10−2* | 1.3* | 2.0 × 10−7* | 6.70* |
| Pyrophosphoric acid | H4P2O7 | 1.2 × 10−1 | 0.91 | 7.9 × 10−3 | 2.10 |
| Resorcinol | C6H4(OH)2 | 4.8 × 10−10 | 9.32 | 7.9 × 10−12 | 11.1 |
| Selenic acid | H2SeO4 | Strong | Strong | 2.0 × 10−2 | 1.7 |
| Selenious acid | H2SeO3 | 2.4 × 10−3 | 2.62 | 4.8 × 10−9 | 8.32 |
| Sulfuric acid | H2SO4 | Strong | Strong | 1.0 × 10−2 | 1.99 |
| Sulfurous acid | H2SO3 | 1.4 × 10−2 | 1.85 | 6.3 × 10−8 | 7.2 |
| meso-Tartaric acid | C4H6O6 | 6.8 × 10−4 | 3.17 | 1.2 × 10−5 | 4.91 |
| Telluric acid | H2TeO4 | 2.1 × 10−8‡ | 7.68‡ | 1.0 × 10−11‡ | 11.0‡ |
| Tellurous acid | H2TeO3 | 5.4 × 10−7 | 6.27 | 3.7 × 10−9 | 8.43 |
| Trichloroacetic acid | CCl3CO2H | 2.2 × 10−1 | 0.66 | ||
| Trifluoroacetic acid | CF3CO2H | 3.0 × 10−1 | 0.52 |
Adapted from UC Davis Chem Wiki (Creative Commons licence): UC Davis GeoWiki by University of California, Davis. CC-BY-NC-SA-3.0
Original source of data: CRC Handbook of Chemistry and Physics, 84th Edition (2004).
