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Chemistry LibreTexts

E1: Acid Dissociation Constants at 25°C

  • Page ID
    9066
  • Name Formula K a1 pKa1 K a2 pKa2 K a3 pKa3 K a4 pKa4
    Acetic acid CH3CO2H 1.75 × 10−5 4.756 - - - - - -
    Arsenic acid H3AsO4 5.5 × 10−3 2.26 1.7 × 10−7 6.76 5.1 × 10−12 11.29 - -
    Benzoic acid C6H5CO2H 6.25 × 10−5 4.204 - - - - - -
    Boric acid H3BO3 5.4 × 10−10* 9.27* >1 × 10−14* >14* - - - -
    Bromoacetic acid CH2BrCO2H 1.3 × 10−3 2.90 - - - - - -
    Carbonic acid H2CO3 4.5 × 10−7 6.35 4.7 × 10−11 10.33 - - - -
    Chloroacetic acid CH2ClCO2H 1.3 × 10−3 2.87 - - - - - -
    Chlorous acid HClO2 1.1 × 10−2 1.94 - - - - - -
    Chromic acid H2CrO4 1.8 × 10−1 0.74 3.2 × 10−7 6.49 - - - -
    Citric acid C6H8O7 7.4 × 10−4 3.13 1.7 × 10−5 4.76 4.0 × 10−7 6.40 - -
    Cyanic acid HCNO 3.5 × 10−4 3.46 - - - - - -
    Dichloroacetic acid CHCl2CO2H 4.5 × 10−2 1.35 - - - - - -
    Fluoroacetic acid CH2FCO2H 2.6 × 10−3 2.59 - - - - - -
    Formic acid CH2O2 1.8 × 10−4 3.75 - - - - - -
    Hydrazoic acid HN3 2.5 × 10−5 4.6 - - - - - -
    Hydrocyanic acid HCN 6.2 × 10−10 9.21 - - - - - -
    Hydrofluoric acid HF 6.3 × 10−4 3.20 - - - - - -
    Hydrogen selenide H2Se 1.3 × 10−4 3.89 1.0× 10−11 11.0 - - - -
    Hydrogen sulfide H2S 8.9 × 10−8 7.05 1 × 10−19 19 - - - -
    Hydrogen telluride H2Te 2.5 × 10−3‡ 2.6 1 × 10−11 11 - - - -
    Hypobromous acid HBrO 2.8 × 10−9 8.55 - - - - - -
    Hypochlorous acid HClO 4.0 × 10−8 7.40 - - - - - -
    Hypoiodous acid HIO 3.2 × 10−11 10.5 - - - - - -
    Iodic acid HIO3 1.7 × 10−1 0.78 - - - - - -
    Iodoacetic acid CH2ICO2H 6.6 × 10−4 3.18 - - - - - -
    Nitrous acid HNO2 5.6 × 10−4 3.25 - - - - - -
    Oxalic acid C2H2O4 5.6 × 10−2 1.25 1.5 × 10−4 3.81 - - - -
    Periodic acid HIO4 2.3 × 10−2 1.64 - - - - - -
    Phenol C6H5OH 1.0 × 10−10 9.99 - - - - - -
    Phosphoric acid H3PO4 6.9 × 10−3 2.16 6.2 × 10−8 7.21 4.8 × 10−13 12.32 - -
    Phosphorous acid H3PO3 5.0 × 10−2* 1.3* 2.0 × 10−7* 6.70* - - - -
    Pyrophosphoric acid H4P2O7 1.2 × 10−1 0.91 7.9 × 10−3 2.10 2.0 × 10−7 6.70 4.8 × 10−10 9.32
    Resorcinol C6H4(OH)2 4.8 × 10−10 9.32 7.9 × 10−12 11.1 - - - -
    Selenic acid H2SeO4 Strong Strong 2.0 × 10−2 1.7 - - - -
    Selenious acid H2SeO3 2.4 × 10−3 2.62 4.8 × 10−9 8.32 - - - -
    Sulfuric acid H2SO4 Strong Strong 1.0 × 10−2 1.99 - - - -
    Sulfurous acid H2SO3 1.4 × 10−2 1.85 6.3 × 10−8 7.2 - - - -
    meso-Tartaric acid C4H6O6 6.8 × 10−4 3.17 1.2 × 10−5 4.91 - - - -
    Telluric acid H2TeO4 2.1 × 10−8‡ 7.68 1.0 × 10−11‡ 11.0 - - - -
    Tellurous acid H2TeO3 5.4 × 10−7 6.27 3.7 × 10−9 8.43 - - - -
    Trichloroacetic acid CCl3CO2H 2.2 × 10−1 0.66 - - - - - -
    Trifluoroacetic acid CF3CO2H 3.0 × 10−1 0.52 - - - - - -
    * Measured at 20°C, not 25°C.
    ‡ Measured at 18°C, not 25°C.