pKa, pKb, Ka and Kb values of common weak acids and bases: acetic, formic, benzoic, hydrofluoric acid, ammonia, amines and more.
| Substance | Formula | pKₐ | pK_b | Kₐ / K_b |
|---|---|---|---|---|
| Sulfuric acid | H2SO4 | 1.92 | 12.08 (A⁻) | 0.012 |
| Acetic acid | CH3COOH | 4.756 | 9.244 (A⁻) | 0.0000175 |
| Formic acid | HCOOH | 3.75 | 10.25 (A⁻) | 0.000178 |
| Benzoic acid | C6H5COOH | 4.204 | 9.796 (A⁻) | 0.0000625 |
| Chloroacetic acid | ClCH2COOH | 2.85 | 11.15 (A⁻) | 0.00141 |
| Hydrofluoric acid | HF | 3.17 | 10.83 (A⁻) | 0.000676 |
| Hydrogen cyanide | HCN | 9.21 | 4.79 (A⁻) | 6.17e-10 |
| Nitrous acid | HNO2 | 3.2 | 10.8 (A⁻) | 0.000631 |
| Phenol | C6H5OH | 9.89 | 4.11 (A⁻) | 1.29e-10 |
| Ammonia | NH3 | 9.21 (BH⁺) | 4.79 | 0.0000162 |
| Methylamine | CH3NH2 | 10.62 (BH⁺) | 3.38 | 0.000417 |
| Dimethylamine | (CH3)2NH | 10.64 (BH⁺) | 3.36 | 0.000437 |
| Trimethylamine | (CH3)3N | 9.76 (BH⁺) | 4.24 | 0.0000575 |
| Ethylamine | C2H5NH2 | 10.65 (BH⁺) | 3.35 | 0.000447 |
| Hydrazine | N2H4 | 8.1 (BH⁺) | 5.9 | 0.00000126 |
| Hydroxylamine | NH2OH | 5.97 (BH⁺) | 8.03 | 9.33e-9 |
pKₐ values from Wikidata (CC0), checked by hand; they are the ones used by the «Solutions (pH)» and «Titration» tools. For bases the pKₐ of the conjugate acid BH⁺ is given and pK_b = 14 − pKₐ; for acids, the pK_b of their conjugate base A⁻, also 14 − pKₐ (Kₐ·K_b = K_w at 25 °C; for polyprotic acids, from the most to the least deprotonated base). H₂SO₄ has a complete 1st dissociation; its pKₐ₂ = 1.92.
Source: Wikidata (CC0 1.0). ↗
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