Table of dissociation constants of substances
Table shows dissociation constants of selected chemical substances in temperature 298K (25°C).

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other inorganic#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
ammoniaNH30.000026--

gases#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
ammoniaNH30.000026--
hydrogen chlorideHCl100000000--
hydrogen cyanideHCN7.5×10-10--
hydrogen fluorideHF0.00063--
hydrogen jodideHI10000000000--
hydrogen sulfurideH2S6×10-81×10-14-
dimethylamine(CH3)2NH0.00051--
trimethylamine(CH3)3N0.0063--
ethylamineC2H5NH20.00047--

inorganic acids#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
hydrogen bromideHBr3000000000--
hydrogen chlorideHCl100000000--
hydrogen cyanideHCN7.5×10-10--
hydrogen fluorideHF0.00063--
hydrogen jodideHI10000000000--
hydrogen sulfurideH2S6×10-81×10-14-
arsenous (III) acidH3AsO36×10-101.7×10-14-
arsenous (V) acidH3AsO40.00561.1×10-73.9×10-12
boric acidH3BO35.8×10-101.8×10-131.6×10-14
hypobromous acidHBrO2×10-9--
bromic (V) acidHBrO30.2--
fulminic acidHCNO0.00012--
carbonic acidH2CO34.5×10-74.7×10-11-
chloric (V) acidHClO36.3--
chloric (I) acidHClO3.2×10-8--
chloric (III) acidHClO20.01--
hypoiodous acidHIO1×10-10--
iodic (V) acidHIO30.16--
iodic (VII) acidHIO40.023--
nitrous (III) acidHNO20.0002--
nitrous (V) acidHNO325--
phosphoric (V) acidH3PO40.00756.3×10-81.3×10-12
sulfurous (IV) acidH2SO30.0166.3×10-8-
sulfurous (VI) acidH2SO410000.012-

phenols#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
phenolC6H5OH1×10-10--

liquids#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
phenolC6H5OH1×10-10--
formic acidHCOOH0.00018--
lactic acidCH3CH(OH)COOH0.00014--
acetate acidCH3COOH0.000018--
propionic acidCH3CH2COOH0.000013--
methylamineCH3NH20.00044--
phenylamine (aniline)C6H5NH23.8×10-10--
hypobromous acidHBrO2×10-9--

carboxylic acids#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
formic acidHCOOH0.00018--
lactic acidCH3CH(OH)COOH0.00014--
oxalic acid(COOH)20.0540.000054-
acetate acidCH3COOH0.000018--
propionic acidCH3CH2COOH0.000013--
salicylic acidOHC6H4COOH0.00131.5×10-14-
benzoic acidC6H5COOH0.0066--

solids#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
oxalic acid(COOH)20.0540.000054-
salicylic acidOHC6H4COOH0.00131.5×10-14-
benzoic acidC6H5COOH0.0066--

amines#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
methylamineCH3NH20.00044--
dimethylamine(CH3)2NH0.00051--
trimethylamine(CH3)3N0.0063--
ethylamineC2H5NH20.00047--
diethylamine(C2H5)2NH0.00085--
triethylamine(C2H5)3N0.00074--
phenylamine (aniline)C6H5NH23.8×10-10--

hydroxides#

SubstanceMolecular formulaFirst dissociation constant K1Second dissociation constant K2Third dissociation constant K3
zinc hydroxideZn(OH)2-0.00004-
copper (II) hydroxideCu(OH)2-0.00013-
iron (II) hydroxideFe(OH)2-0.00013-
iron (III) hydroxideFe(OH)3-0.0025-
aluminium hydroxideAl(OH)3--1.4×10-9
silver (I) hydroxideAgOH0.00011--

Some facts#

  • Dissociation constant is equilibrium constant written for the dissociation reaction.
  • If some acid dissociates in the aqueous solution proceeds according to the reaction:
    HA+H2O    H3O++AHA + H_2O \iff H_3O^+ + A^-
    then we can write the following dissociation constant for it:
    K=[H3O+][A][HA][H2O]K=\dfrac{[H_{3}O^{+}][A^{-}]}{[HA][H_{2}O]}
    where:
    • KK - dissociation constant of HAHA acid,
    • [HA][HA] - molar concentration of not dissociated acid HAHA in an equilibrium state,
    • [H2O][H_2O] - molar concentration of water (solvent) in an equilibrium state,
    • [H3O+][H_3O^+] - molar concentration of hydronium ions H3O+H_3O^+ in an equilibrium state,
    • [A][A^-] - molar concentration of acid anions in equilibrium.
  • Analogously if some alkali dissociates according to the reaction:
    BOH+H2O    BH++OHBOH + H_2O \iff BH^+ + OH^-
    then we can write following dissociation constant:
    K=[BH+][OH][BOH][H2O]K=\dfrac{[BH^+][OH^{-}]}{[BOH][H_{2}O]}
    where:
    • KK - dissociation constant of BOHBOH alkali,
    • [BOH][BOH] - molar concentration of not dissociatedBOHBOH alkali in equlibrium state,
    • [H2O][H_2O] - molar concentration of water (solvent) in an equlibrium state,
    • [BH+][BH^+] - molar concentration of BH+BH^+ cations in equlibrium state,
    • [OH][OH^-] - molar concentartion of hydroxyl ions OHOH^- in equlibrium state.
  • Other name for dissociation constant is ionization constant.
  • Dissociation constant is specific for given substance.
  • The dissociation constant (just like the equilibrium constant of other chemical reactions) depends on the temperature. Chemical tables usually give values for 278K (25°C) i.e. room temperature.

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