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
Dimethylsulfoxide		35
Ammonia		36
Diisopropylamine		40
Toluene		41
Benzene		43
Propene		43
Ethene		44
Methane		approx. 60

a. 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.
b. The strength of a base is related to the pK_a of its conjugate acid as pK_b = 14 - pK_a.