APPENDIX B: Acidity Constants

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pKa values of some acids

Acid

pKa (at 25°C)

Acid

pKa (at 25°C)

Acetic acid

  4.76

Malic acid, pK1

  3.40

Acetoacetic acid

  3.58

pK2

  5.11

Ammonium ion

  9.25

Phenol

  9.89

Ascorbic acid, pK1

  4.10

Phosphoric acid, pK1

  2.12

                       pK2

11.79

                          pK2

  7.21

Benzoic acid

  4.20

                          pK3

12.67

n-Butyric acid

  4.81

Pyridinium ion

  5.25

Cacodylic acid

  6.19

Pyrophosphoric acid, pK1

  0.90

Citric acid, pK1

  3.14

                                 pK2

  2.00

                 pK2

  4.77

                                 pK3

  6.60

                 pK3

  6.39

                                 pK4

  9.40

Ethylammonium ion

10.81

Succinic acid, pK1

  4.21

Formic acid

  3.75

                      pK2

  5.64

Glycine, pK1

  2.35

Trimethylammonium ion

  9.79

             pK2

  9.78

Tris (hydroxymethyl) aminomethane

  8.08

Imidazolium ion

  6.95

Water*

15.74

Lactic acid

  3.86

 

 

Fumaric acid, pK1

  3.03

 

 

                     pK2

  4.44

 

 

*[H+][OH] = 10−14; [H2O] = 55.5 M.

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