This is “Appendix C: Dissociation Constants and pKa Values for Acids at 25°C”, appendix 3 from the book Principles of General Chemistry (index.html) (v. 1.0).
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i Chapter 27
Appendix C: Dissociation Constants and pKa Values for Acids at 25°C
Name Formula K a1 pKa1 K a2 pKa2 K a3 pKa3 K a4 pKa4
−5 Acetic acid CH3CO2H 1.75 × 10 4.756
−3 −7 −12 Arsenic acid H3AsO4 5.5 × 10 2.26 1.7 × 10 6.76 5.1 × 10 11.29
−5 Benzoic acid C6H5CO2H 6.25 × 10 4.204
−10 −14 Boric acid H3BO3 5.4 × 10 * 9.27* >1 × 10 * >14*
Bromoacetic −3 CH2BrCO2H 1.3 × 10 2.90 acid
−7 −11 Carbonic acid H2CO3 4.5 × 10 6.35 4.7 × 10 10.33
Chloroacetic −3 CH2ClCO2H 1.3 × 10 2.87 acid
−2 Chlorous acid HClO2 1.1 × 10 1.94
−1 −7 Chromic acid H2CrO4 1.8 × 10 0.74 3.2 × 10 6.49
−4 −5 −7 Citric acid C6H8O7 7.4 × 10 3.13 1.7 × 10 4.76 4.0 × 10 6.40
Cyanic acid HCNO 3.5 × 10−4 3.46
Dichloroacetic −2 CHCl2CO2H 4.5 × 10 1.35 acid
Fluoroacetic −3 CH2FCO2H 2.6 × 10 2.59 acid
−4 Formic acid CH2O2 1.8 × 10 3.75
−5 Hydrazoic acid HN3 2.5 × 10 4.6
Hydrocyanic HCN 6.2 × 10−10 9.21 acid
Hydrofluoric HF 6.3 × 10−4 3.20 acid
* Measured at 20°C, not 25°C.
‡ Measured at 18°C, not 25°C.
2990 Chapter 27 Appendix C: Dissociation Constants and pKa Values for Acids at 25°C
Name Formula K a1 pKa1 K a2 pKa2 K a3 pKa3 K a4 pKa4
Hydrogen −4 −11 H2Se 1.3 × 10 3.89 1.0× 10 11.0 selenide
Hydrogen −8 −19 H2S 8.9 × 10 7.05 1 × 10 19 sulfide
Hydrogen −3‡ ‡ −11 H2Te 2.5 × 10 2.6 1 × 10 11 telluride
Hypobromous HBrO 2.8 × 10−9 8.55 acid
Hypochlorous HClO 4.0 × 10−8 7.40 acid
Hypoiodous HIO 3.2 × 10−11 10.5 acid
−1 Iodic acid HIO3 1.7 × 10 0.78
−4 Iodoacetic acid CH2ICO2H 6.6 × 10 3.18
−4 Nitrous acid HNO2 5.6 × 10 3.25
−2 −4 Oxalic acid C2H2O4 5.6 × 10 1.25 1.5 × 10 3.81
−2 Periodic acid HIO4 2.3 × 10 1.64
−10 Phenol C6H5OH 1.0 × 10 9.99
Phosphoric −3 −8 −13 H3PO4 6.9 × 10 2.16 6.2 × 10 7.21 4.8 × 10 12.32 acid
Phosphorous −2 −7 H3PO3 5.0 × 10 * 1.3* 2.0 × 10 * 6.70* acid
Pyrophosphoric −1 −3 −7 −10 H4P2O7 1.2 × 10 0.91 7.9 × 10 2.10 2.0 × 10 6.70 4.8 × 10 9.32 acid
−10 −12 Resorcinol C6H4(OH)2 4.8 × 10 9.32 7.9 × 10 11.1
−2 Selenic acid H2SeO4 Strong Strong 2.0 × 10 1.7
−3 −9 Selenious acid H2SeO3 2.4 × 10 2.62 4.8 × 10 8.32
−2 Sulfuric acid H2SO4 Strong Strong 1.0 × 10 1.99
−2 −8 Sulfurous acid H2SO3 1.4 × 10 1.85 6.3 × 10 7.2
meso-Tartaric −4 −5 C4H6O6 6.8 × 10 3.17 1.2 × 10 4.91 acid
* Measured at 20°C, not 25°C.
‡ Measured at 18°C, not 25°C.
2991 Chapter 27 Appendix C: Dissociation Constants and pKa Values for Acids at 25°C
Name Formula K a1 pKa1 K a2 pKa2 K a3 pKa3 K a4 pKa4
−8‡ ‡ −11‡ ‡ Telluric acid H2TeO4 2.1 × 10 7.68 1.0 × 10 11.0
−7 −9 Tellurous acid H2TeO3 5.4 × 10 6.27 3.7 × 10 8.43
Trichloroacetic −1 CCl3CO2H 2.2 × 10 0.66 acid
Trifluoroacetic −1 CF3CO2H 3.0 × 10 0.52 acid
* Measured at 20°C, not 25°C.
‡ Measured at 18°C, not 25°C.
Source of data: CRC Handbook of Chemistry and Physics, 84th Edition (2004).
2992