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Acid / Base pKa Values

Free Acid or Base Molecular Wt pKa at 25C
Pyrophosphoric 177.98 0.85 (pKa1)
Oxalic 95.07 1.19 (pKa1)
Glycerophosphoric 172.08 1.47 (pKa1)
Ethylenediamine tetraacetic acid (EDTA) 292.24 1.70 (pKa1)
Histidine 155.16 1.82 (pKa1)
Pyrophosphoric 177.98 1.96 (pKa2)
Maleic 16.07 2.00 (pKa1)
Benzenehexacarboxylic (mellitic) 342.17 2.08 (pKa1)
Phosphoric 98.0 0 2.12 (pKa1)
Brucine tetrahydrate 466.53 2.30 (pKa1)
Benzenepentacarboxylic 296.18 2.34 (pKa1)
Glycine 75.07 2.34 (pKa1)
Benzene-1,2,4,5-tetracarboxylic (pyromellitic) 254.15 2.43 (pKa1)
Benzenehexacarboxylic (mellitic) 342.17 2.46 (pKa2)
EDTA 292.24 2.60 (pKa2)
Malonic 146.02 2.85 (pKa1)
Phthalic 116.13 2.90
Benzenepentacarboxylic 298.16 2.95 (pKa2)
Salicylic 138.12 2.98
Benzene-1,2,3-tricarboxylic (hemimellitic) 246.18 2.98 (pKa1)
1,4-Piperazinebis-(ethanesulfonic acid) "PIPES" 302.37 3.00 (pKa3)
Tartaric 150.09 3.02 (pKa1)
Fumaric 116.07 3.03 (pKa1)
Glycylglycine 132.12 3.06
Citric acid 192.12 3.06 (pKa1)
Cyclopentanetetra-1,2,3,4-carboxylic 246.17 3.07 (pKa1)
o-Phthalic 166.13 3.10 (pKa1)
Benzene-1,2,4,5-tetracarboxylic (pyromellitic) 254.15 3.13 (pKa2)
Benzene-1,3,5-tricarboxylic (trimesic) 210.14 3.16 (pKa1)
Benzenehexacarboxylic (mellitic) 342.17 3.24 (pKa3)
Dimethylmalonic 132.12 3.29 (pKa1)
Mandelic 152.15 3.36
Butane-1,2,3,4-tetracarboxylic 234.12 1 3.36 (pKa)
Malic 134.09 3.40 (pKa1)
I,l-Cyclohexanediacetic 200.18 3.52 (pKal)
2-Methylpropane-1,2,3-triscarboxylic 190.15 3.53 (pKal)
Hippuric 179.18 3.64
Propane-1,2,3-tricarboxylic (tricarballylic) 176.12 3.67(pKa1)
Formic 46.02 3.75
3,3-Dimethylglutaric 160.17 3.79 (pKal)
I,l-Cyclopentanediacetic 186.21 3.82 (pKa1)
Itaconic 130.1 3.84 (pKa1)
Lactic 90.08 3.86
Benzenepentacarboxylic 298.16 3.94 (pKa3)
Benzene-1,3,5-tricarboxylic (trimesic) 210.14 3.98 (pKa2)
Barbituric 128.09 3.98
Ascorbic 176.12 4.10 (pKa1)
2,2-Dimethflsuccinic 146.14 4.11 (pKa1)
Succinic 118.09 4.19 (pKa1)
Benzoic 122.12 4.20
Oxalic 95 07 4.21 (pKa2)
Benzene-1,2,3-tricarboxylic (hemimellitic) 246.18 4.25 (pKa2)
3,6-Endomethylene-1,2,3,6-tetrahydrophthalic acid "EMTA" 183.62 4.30 (pKa1)
2,2-Dimethylglutaric 160.17 4.31 (pKa1)
Butane-1,2,3,4-tetracarboxylic 234.12 4.38 (pKa2)
Benzenehexacarboxylic (mellitic) 342.17 4.44 (pKa4)
Benzene-1,2,4,5-tetracarboxylic (pyromellitic) 254.15 4.44 (pKa3)
Fumaric 116.07 4.47 (pKa2)
Cyclopentanetetra-1,2,3,4-carboxylic 246.17 4.48 (pKa2)
Tartaric 150.09 4.54 (pKa2)
Citric 210.14 4.74 (pKa2)
Acetic 60.05 4.76
n-Butyric 88.1 0 4.82
Propane-1,2,3-tricarboxylic (tricarballylic) 176.12 4.84 (pKa2)
Benzene-1,3,5-tricarboxylic (trimesic) 210.14 4.85 (pKa3)
Propionic 74.08 4.87
2-Methylpropane-1,2,3-triscarboxylic 190.15 5.02 (pKa2)
Malic 134.09 5.05 (pKa2)
Benzenepentacarboxylic 298.16 5.07 (pKa4)
Pyridine 79.1 5.23
o-Phthalic 116.13 5.27 (pKa2)
Citric 192.12 5.40 (pKa3)
Butane-1,2,3,4-tetracarboxylic 234.12 5.45 (pKa3)
Benzenehexacarboxylic (mellitic) 342.17 5.50 (pKa5)
2,2-Dimethylglutaric 160.17 5.51 (pKa2)
Itaconic 130.1 5.55 (pKa2)
Cyclopentanetetra-1,2,3,4-carboxylic 246.17 5.57 (pKa3)
Succinic 118.09 5.57 (pKa2)
Benzene-1,2,4,5-tetracarboxylic (pyromellitic) 254.15 5.61 (pKa4)
Benzene-1,2,3-tricarboxylic (hemimellitic) 246.18 5.87 (pKa3)
Dimethylmalonic 132.12 5.98 (pKa2)
Histidine 156.16 6.00 (pKa2)
Hydroxylamine 34.0 6.03
Carbonic (H2CO3+C02) 62(C02) 6.10 (pKa1)
Malonic 104.06 6.10 (pKa2)
2-(N-Morpholino)-ethane sulfonic acid "MES" 195.2 6.15 (pKa2)
Glycerophosphoric 172.08 6.19 (pKa2)
Propane-1,2,3-tricarboxylic (tricarballylic) 176.12 6.20(pKa3)
Benzenepentacarboxylic 298.16 6.25 (pKa5)
Maleic 116.07 6.26 (pKa2)
2,2-Dimethylsuccinic 146.14 6.29 (pKa2)
EDTA 292.24 6.30 (pKa3)
3,3-Dimethylglutaric 160.17 6.31 (pKa2)
Bis(2-hydroxyethyl)imino-tris(hydroxymethyl) methane "BIS-TRIS" 209.24 6.46
Benzenehexacarboxylic (mellitic) 342.17 6.59 (pKa6)
N-(2-Acetamido)imino-diacetic acid "ADA" 190.17 6.60 (pKa3)
Butane-1,2,3,4-tetracarboxylic 234.12 6.63 (pKa4)
Pyrophosphoric 177.98 6.68 (pKa3)
I,l-Cyclopentanediacetic (3,3 tetramethylene glutaric acid) 186.21 6.70 (pKa2)
1,4-Piperazinebis-(ethanesulfonic acid) "PIPES" 302.37 6.8 (pKa4)
N-(2-Acetamido)-2-aminoethanesulfonic acid "ACES" 182.20 6.9 (pKa2)
I,l-Cyclohexanediacetic 200.18 6.94 (pKa2)
3,6-Endomethylene- 1,2,3,6-tetrahydrophthalicacid "EMTA" 183.62 7.00 (pK2)
Imidazole 68.08 7.00
2-(Aminoethyl)trimethylammonium chloride "CHOLAMINE" 156.69 7.10
N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid "BES" 213.25 7.15 (pKa2)
2-Methylpropane- 1,2,3-triscarboxylic 190.15 7.20 (pKa3)
2-(N-Morpholino)propane-sulfonic acid "MOPS" 209.27 7.20 (pKa2)
Phosphoric 98.0 7.21 (pKa2)
N-Tris(hydroxymethyl)methyl-2-aminoethane sulfonic acid "TES" 229.28 7.50 (pKa2)
N-2-Hydroxyethylpiperazine-N'-2-ethanesulfonic acid "HEPES" 238.31 7.55 (pKa2)
2-Hydroxyethylimino-tris(hydroxymethyl)methane "MONO-TRIS" 165.18 7.83
Brucine tetrahydrate 466.53 7.95 (pKa2)
4-(2-Hydroxyethyl)- I -piperazinepropane sulfonic acid "EPPS" 252.23 8.00
Tris(hydroxymethyl)aminomethane"TRIS" 121.14 8.10
N-Tris(hydroxymethyl)methylglycine "TRICINE" 180.18 8.15
Glycinamide 74.04 8.20
N,N-Bis(2-hydroxyethyl)glycine"BICINE" 163.18 8.35
N-Tris(hydroxymethyl)methyl-2-aminopropane sulfonic acid "TAPS" 243.3 8.40 (pKa2)
N-Glycyl-glycine 132.12 8.40
Histidine 155.16 9.17 (pKa3)
Boric 43.82 9.24
Pyrophosphoric 177.98 9.39 (pKa4)
Ethanolamine 61.08 9.44
Glycine 75.07 9.60 (pKa2)
Trimethylamine 59.11 9.74
Cyclopentanetetra-1,2,3,4-carboxylic 246.17 10.06 (pKa4)
Carbonic (H2CO3 + CO2) 62(CO2) 10.25 (pKa2)
3-Cyclohexylamino-l-propanesulfonic acid "CAPS" 221.32 10.40 (pKa2)
EDTA 292.24 10.60 (pKa4)
Methylamine 31.06 10.64
Dimethylamine 45.09 10.72
Ethylamine 45.09 10.75
Triethylamine 101.19 10.76
Diethylamine 73.14 10.98
Ascorbic 176.12 11.79 (pKa2)
Phosphoric 98.00 12.32 (pKa3)

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