Acid-Base Ionization Constant
Ionization Constants for Select Acids (a table for bases is below)
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+ + H2AsO4−
|
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 |
|
Butyric
|
CH3CH2CH2COOH + H2O ⇌ H3O+ + CH3CH2CH2COO- |
1.5 × 10-5 |
4.82 |
|
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 | |
|
Chloroacetic
|
CH2ClCOOH + H2O ⇌ H3O+ + CH2ClCOO- |
1.4 × 10-3 |
2.85 |
|
4-chlorobutyric
|
CH2ClCH2CH2COOH + H2O ⇌ H3O+ + CH2ClCH2CH2COO- |
3.0 × 10-5 |
4.53 |
|
3-chlorobutyric acid
|
CH3CHClCH2COOH + H2O ⇌ H3O+ + CH3CHClCH2COO- |
8.9 × 10-5 |
4.05 |
|
2-chlorobutyric acid
|
CH3CH2CHClCOOH + H2O ⇌ H3O+ + CH3CH2CHClCOO- |
1.3 × 10-3 |
2.89 |
|
Chlorous
|
HClO2 + H2O ⇌ H3O+ + ClO2−
|
1.1 × 10−2
|
1.96 |
|
Dichloroacetic
|
CHCl2COOH + H2O ⇌ H3O+ + CHCl2COO- |
4.5 × 10-2 |
1.35 |
|
Formic
|
HCOOH + H2O ⇌ H3O+ + HCOO−
|
1.8 × 10−4
|
3.75 |
|
Hydrazoic
|
HN3 + H2O ⇌ H3O+ + N3−
|
1.0 × 10−5
|
5.00 |
|
Hydrochloric
|
HCl + H2O ⇌ H3O+ + Cl- |
1.2 × 106 |
-6.1 |
|
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 | |
|
Hypobromous
|
HOBr + H2O ⇌ H3O+ + OBr- |
3 × 10-9 |
8.5 |
|
Hypochlorous
|
HOCl + H2O ⇌ H3O+ + OCl−
|
6.8 × 10−8
|
7.17 |
|
Hypoiodous
|
HOI + H2O ⇌ H3O+ + OI- |
3 × 10-11 |
10.5 |
|
Nitric
|
HNO3 + H2O ⇌ H3O+ + NO3- |
27 |
-1.43 |
|
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 = 4.0 × 103
|
-3.6 |
|
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 | |
|
Trichloroacetic
|
CCl3COOH + H2O ⇌ H3O+ + CCl3COO- |
0.17 |
0.77 |
|
Trifluoroacetic
|
CF3COOH + H2O ⇌ H3O+ + CF3COO- |
0.30 |
0.52 |
| 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. Also from Serjeant, E. P. and Dempsey, B. (eds.), “Ionization Constants of Organic Acids in Aqueous Solution,” IUPAC Chemical Data Series No. 23, Pergamon Press, Oxford, 1979. †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 |
|---|---|---|---|
|
Acetylide
|
C2H- + H2O ⇌ OH- + C2H2 |
1 × 1011 |
-11 |
|
Amide
|
NH2- + H2O ⇌ OH- + NH3 |
1 × 1020 |
-20 |
|
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 |
|
Ethoxide
|
CH3CH2O- + H2O ⇌ OH- + CH3CH2OH |
1 × 102 |
-2 |
|
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 | |
|
Hydride
|
H- + H2O ⇌ OH- + H2 |
1 × 1021 |
-21 |
|
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. Also from Serjeant, E. P. and Dempsey, B. (eds.), “Ionization Constants of Organic Acids in Aqueous Solution,” IUPAC Chemical Data Series No. 23, Pergamon Press, Oxford, 1979. ‡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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