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Chapter 27 Appendix C: Dissociation Constants and pKa Values for Acids at 25°C
| Name | Formula | K a1 | pKa1 | K a2 | pKa2 | K a3 | pKa3 | K a4 | pKa4 |
|---|---|---|---|---|---|---|---|---|---|
| Acetic acid | CH3CO2H | 1.75 × 10−5 | 4.756 | ||||||
| Arsenic acid | H3AsO4 | 5.5 × 10−3 | 2.26 | 1.7 × 10−7 | 6.76 | 5.1 × 10−12 | 11.29 | ||
| 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 | 4.0 × 10−7 | 6.40 | ||
| 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 | 4.8 × 10−13 | 12.32 | ||
| 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 | 2.0 × 10−7 | 6.70 | 4.8 × 10−10 | 9.32 |
| 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 | ||||||
| * Measured at 20°C, not 25°C. | |||||||||
| ‡ Measured at 18°C, not 25°C. | |||||||||
Source of data: CRC Handbook of Chemistry and Physics, 84th Edition (2004).