pKa Values for Organic and Inorganic
Bronsted Acids at 25 oC
Acid strengths decrease down the tablea.
Conjugate base strengths increase down the tableb.
| Name |
Acid / Conjugate base |
pKa |
| Sulfuric acid |
 |
-10 |
| Hydrogen iodide |
 |
-10 |
| Hydrogen bromide |
 |
-9 |
| Hydrogen chloride |
 |
-7 |
| Acetone conjugate acid |
 |
-7 |
| Benzenesulfonic acid |
 |
-6.5 |
| Acetic acid conjugate acid |
 |
-6 |
| Diethyl ether conjugate acid |
 |
-3.5 |
| Ethanol conjugate acid |
 |
-2 |
| Methanesulfonic acid |
 |
-2 |
| Hydronium ion |
 |
-1.74 |
| Nitric acid |
 |
-1.5 |
| Trifluoroacetic acid |
 |
0.5 |
| Bisulfate ion |
 |
2.0 |
| Benzoic acid |
 |
4.2 |
| Anilinium ion |
 |
4.6 |
| Acetic acid |
 |
4.8 |
| Pyridinium ion |
 |
5.2 |
| Carbonic acid |
 |
6.4 |
| Thiophenol |
 |
6.6 |
| Hydrogen sulfide |
 |
7.0 |
| Peracetic acid |
 |
8.2 |
| Phthalimide |
 |
8.3 |
| Nitroethane |
 |
8.5 |
| Pentane-2,4-dione |
 |
9.0 |
| Ammonium ion |
 |
9.3 |
| Hydrogen cyanide |
 |
9.3 |
| Hexaflurorisopropanol |
 |
9.3 |
| Phenol |
 |
9.9 |
| Bicarbonate ion |
 |
10.3 |
| Methanethiol |
 |
10.3 |
| Ethylammonium ion |
 |
10.8 |
| Diethyl malonate |
 |
12.9 |
| Guanidinium ion |
 |
13.6 |
| Cyclopentadiene |
 |
15.0 |
| Water |
 |
15.74 |
| Ethanol |
 |
16.0 |
| Cyclohexanone |
 |
16.7 |
| Acetamide |
 |
17 |
| Isopropanol |
 |
17.1 |
| t-Butanol |
 |
18.0 |
| Acetone |
 |
19.3 |
| Ethyl acetate |
 |
25 |
| Ethyne |
 |
25 |
| Acetonitrile |
 |
25 |
| Dimethylsulfone |
 |
28 |
| Diemthylsulfoxide |
 |
35 |
| Ammonia |
 |
36 |
| Diisopropylamine |
 |
40 |
| Toluene |
 |
41 |
| Benzene |
 |
43 |
| Propene |
 |
43 |
| Ethene |
 |
44 |
| Methane |
 |
approx. 60 |
- For strengths of organic acids see E. P. Serjeant and B. Dempsey
(eds.), Ionization Constants of Organic Acids in Solution,
IUPAC Chemical Data Series No. 23, Pergamon Press, Oxford, UK,
1979.
- The strength of a base is related to the pKa of its
conjugate acid as pKb = 14 - pKa.