Appendix I: Ionization Constants of Selected Weak Acids and Bases
Ionization Constants for Select Acids
Ka determined at 25 °C.
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| Acid | Formula and Ionization Equation | Ka | pKa |
|---|---|---|---|
| Acetic | CH3COOH + H2O ⇌ H3O+ + CH3COO- | 1.8 × 10-5 | 4.74 |
| Arsenic | H3AsO4 + H2O ⇌ H3O+ + H3AsO4- | K1 = 6.17 × 10-3 | 2.210 |
| H2AsO4- + H2O ⇌ H3O+ + HAsO42- | K2 = 1.17 × 10-7 | 6.932 | |
| HAsO42- + H2O ⇌ H3O+ + AsO43- | K3 = 3.09 × 10-12 | 11.523 | |
| Benzoic | C6H5COOH + H2O ⇌ H3O+ + C6H5COO- | 1.2 × 10-4 | 3.92 |
| Boric | B(OH)3(H2O) + H2O ⇌ H3O+ + B(OH)4- | 5.8 × 10-10 | 9.24 |
| Carbonic | H2CO3 + H2O ⇌ H3O+ + HCO3- | K1 = 4.3 × 10-7 | 6.37 |
| HCO3- + H2O ⇌ H3O+ + CO32- | K2 = 4.7 × 10-11 | 10.33 | |
| Citric | H3C6H5O7 + H2O ⇌ H3O+ + H2C6H5O7- | K1 = 1.4 × 10-3 | 2.85 |
| H2C6H5O7- + H2O ⇌ H3O+ + HC6H5O72- | K2 = 4.5 × 10-5 | 4.35 | |
| HC6H5O72- + H2O ⇌ H3O+ + C6H5O73- | K3 = 1.5 × 10-6 | 5.82 | |
| Chlorous | HClO2 + H2O ⇌ H3O+ + ClO2- | 1.1 × 10-2 | 1.96 |
| Formic | HCOOH + H2O ⇌ H3O+ + HCOO- | 3.0 × 10-4 | 3.52 |
| Hydrazoic | HN3 + H2O ⇌ H3O+ + N3- | 1.0 × 10-5 | 5.00 |
| Hydrocyanic | HCN + H2O ⇌ H3O+ + CN- | 3.3 × 10-10 | 9.48 |
| Hydrofluoric | HF + H2O ⇌ H3O+ + F- | 6.8 × 10-4 | 3.17 |
| Hydrogen peroxide | H2O2 + H2O ⇌ H3O+ + HO2- | 2.1 × 10-12 | 11.68 |
| Hydrosulfuric† | H2S + H2O ⇌ H3O+ + HS- | K1 = 1 × 10-7 | 7.0 |
| HS- + H2O ⇌ H3O+ + S2- | K2 = 1 × 10-19 | 19.0 | |
| Hypochlorous | HOCl + H2O ⇌ H3O+ + OCl- | 6.8 × 10-8 | 7.17 |
| Nitrous | HNO2 + H2O ⇌ H3O+ + NO2- | 7.41 × 10-4 | 3.130 |
| Oxalic | H2C2O4 + H2O ⇌ H3O+ + HC2O4- | K1 = 5.5 × 10−2 | 1.26 |
| HC2O4- + H2O ⇌ H3O+ + C2O42- | K2 = 1.4 × 10−4 | 3.85 | |
| Phenol | HC6H5O + H2O ⇌ H3O+ + C6H5O- | 1.7 × 10-10 | 9.77 |
| Phosphoric | H3PO4 + H2O ⇌ H3O+ + H2PO4- | K1 = 7.2 × 10-3 | 2.14 |
| H2PO4- + H2O ⇌ H3O+ + HPO42- | K2 = 6.3 × 10-8 | 7.20 | |
| HPO42- + H2O ⇌ H3O+ + PO43 | K3 = 4.6 × 10-13 | 12.34 | |
| Phosphorous | H3PO3 + H2O ⇌ H3O+ + H2PO3- | K1 = 2.4 × 10-2 | 1.62 |
| H2PO3- + H2O ⇌ H3O+ + HPO32- | K2 = 2.9 × 10-7 | 6.54 | |
| Propanoic | CH3CH2COOH + H2O ⇌ H3O+ + CH3CH2COO- | 1.33 × 10-5 | 4.85 |
| Selenic | H2SeO4 + H2O ⇌ H3O+ + HSeO4- | K1 = very large | --- |
| HSeO4- + H2O ⇌ H3O+ + SeO42- | K2 = 2.2 × 10-2 | 1.66 | |
| Selenous | H2SeO3 + H2O ⇌ H3O+ + HSeO3- | K1 = 2.5 × 10-3 | 2.60 |
| HSeO3- + H2O ⇌ H3O+ + SeO32- | K2 = 1.6 × 10-9 | 8.80 | |
| Sulfuric | H2SO4 + H2O ⇌ H3O+ + HSO4- | K1 = very large | --- |
| HSO4- + H2O ⇌ H3O+ + SO42- | K2 = 1.1 × 10-2 | 1.96 | |
| Sulfurous | H2SO3 + H2O ⇌ H3O+ + HSO3- | K1 = 1.7 × 10-2 | 1.77 |
| HSO3- + H2O ⇌ H3O+ + SO32- | K2 = 6.3 × 10-8 | 7.2 | |
| Tellurous | H2TeO3 + H2O ⇌ H3O+ + HTeO3- | K1 = 7.1 × 10-7 | 6.15 |
| HTeO3- + H2O ⇌ H3O+ + TeO32- | K2 = 4.0 × 10-9 | 8.40 | |
| Taken from Hogfeldt, E. and Perrin, D. D., Stability Constants of Metal-Ion complexes, 1st ed. Oxford: New York: Pergamon, 1979-1982. International Union of Pure and Applied Chemistry Commission on Equilibrium Data. †From Myers, R., Journal of Chemical Education, Vol. 63, 1986, pp. 687-690. |
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Ionization Constants for Select Bases
Kb determined at 25 °C.
| Base | Formula and Ionization Equation | Kb | pKb |
|---|---|---|---|
| Ammonia ‡ | NH3 + H2O ⇌ NH4+ + OH− | 1.77 × 10−5 | 4.752 |
| Aniline§ | C6H5NH2 + H2O ⇌ C6H5NH3+ + OH− | 3.9 × 10−10 | 9.41 |
| Dimethylamine§ | (CH3)2NH + H2O ⇌ (CH3)2NH2+ + OH− | 5.8 × 10−4 | 3.24 |
| Ethylenediamine | (CH2)2(NH2)2 + H2O ⇌ (CH2)2(NH2)2H+ + OH− | K1 = 7.8 × 10−5 | 4.11 |
| (CH2)2(NH2)2H+ + H2O ⇌ (CH2)2(NH2)2H22+ + OH− | K2 = 2.1 × 10−8 | 7.68 | |
| Hydrazine | N2H4 + H2O ⇌ N2H5+ + OH− | K1 = 1.2 × 10−6 | 5.92 |
| N2H5+ + H2O ⇌ N2H62+ + OH− | K2 = 1.3 × 10−15 | 14.89 | |
| Hydroxylamine | NH2OH + H2O ⇌ NH3OH+ + OH− | 9.3 × 10−9 | 8.03 |
| Methylamine | CH3NH2 + H2O ⇌ CH3NH3+ + OH− | 5.0 × 10−4 | 3.30 |
| Pyridine | C5H5N + H2O ⇌ C5H5NH+ + OH− | 1.6 × 10−9 | 8.80 |
| Trimethylamine§ | (CH3)3N + H2O ⇌ (CH3)3NH+ + OH− | 6.2 × 10−5 | 4.21 |
| Taken from Hogfeldt, E. and Perrin, D. D., Stability Constants of Metal-Ion complexes, 1st ed. Oxford: New York: Pergamon, 1979-1982. International Union of Pure and Applied Chemistry Commission on Equilibrium Data. ‡From Read, A. J., Journal of Solution Chemistry, Vol. 11, No. 9, 1982, pp. 649-664. §From Meites, L., Ed. Handbook of Analytical Chemistry, 1st ed. New York: McGraw-Hill, 1963. |
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