Chemistry Reference

pKa Table of Common Acids in Water and DMSO

Searchable pKa table with 131 acids: aqueous and DMSO values, conjugate bases, sources and a deprotonation check. Printable.

131 acids with conjugate bases and sourcesAqueous and DMSO values, extrapolated ones flaggedCan base X deprotonate acid Y? ΔpKa, K and percentPNG, SVG and print, no sign-up

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Showing 131 of 131 acids

  • −14extrapolatedWater, E

    CF3SO3H→CF3SO3−

    Inorganic acids

  • −10extrapolatedWater, W

    HI→I−

    Inorganic acids

  • −10extrapolatedWater, E, W

    HClO4→ClO4−

    Inorganic acids

  • −9.0extrapolatedWater, E, W

    HBr→Br−

    Inorganic acids

  • −8.0extrapolatedWater, E

    HCl→Cl−

    Inorganic acids

  • −7.8extrapolatedWater, E

    PhC(OH)2+→PhCOOH

    Protonated species

  • −6.2extrapolatedWater, E

    PhC(OH)CH3+→PhCOCH3

    Protonated species

  • −3.8extrapolatedWater, E

    (CH3)2OH+→(CH3)2O

    Protonated species

  • −3.0extrapolatedWater, E, W

    H2SO4→HSO4−

    Inorganic acids

    First dissociation, complete in water.

  • −2.6extrapolatedWater, E

    CH3SO3H→CH3SO3−

    Inorganic acids

    Williams prints -0.6. This page follows Ripin and Evans.

  • −1.3extrapolatedWater, E

    HNO3→NO3−

    Inorganic acids

  • −0.25extrapolatedWater, E

    CF3COOH→CF3COO−

    Carboxylic acids

  • 0.0Water, E

    H3O+→H2O

    Inorganic acids

    Ripin and Evans (2024) define H₃O⁺ as 0.0 on the same 1 M scale as every other row. Many organic textbooks print -1.74 (Kw divided by 55.5 M); that convention is inconsistent with how the other pKa values are defined.

  • 0.3DMSO, E

    CF3SO3H→CF3SO3−

    Inorganic acids

  • 0.65Water, E, W

    Cl3CCOOH→Cl3CCOO−

    Carboxylic acids

  • 0.9DMSO, E, B

    HBr→Br−

    Inorganic acids

  • 1.23Water, W

    HOOC-COOH→HOOC-COO−

    Carboxylic acids

  • 1.29Water, E

    Cl2CHCOOH→Cl2CHCOO−

    Carboxylic acids

  • 1.6DMSO, E

    CH3SO3H→CH3SO3−

    Inorganic acids

  • 1.8DMSO, E, B

    HCl→Cl−

    Inorganic acids

  • 1.9Water, E, W

    H2SO3→HSO3−

    Inorganic acids

  • 1.92Water, E

    cis-HOOCCH=CHCOOH→cis-HOOCCH=CHCOO−

    Carboxylic acids

  • 1.99Water, E, W

    HSO4−→SO42−

    Inorganic acids

  • 2.12Water, E, W

    H3PO4→H2PO4−

    Inorganic acids

  • 2.86Water, E

    ClCH2COOH→ClCH2COO−

    Carboxylic acids

  • 3.17Water, E

    HF→F−

    Inorganic acids

  • 3.29Water, E, W

    HNO2→NO2−

    Inorganic acids

  • 3.4DMSO, E

    Pyridine-H+→Pyridine

    Ammonium and cations

  • 3.44Water, E

    p-O2NC6H4COOH→p-O2NC6H4COO−

    Carboxylic acids

  • 3.6DMSO, E

    PhNH3+→PhNH2

    Ammonium and cations

    Reich-Bordwell prints 3.8.

  • 3.77Water, E, W

    HCOOH→HCOO−

    Carboxylic acids

  • 4.19Water, W

    HOOC-COO−→−OOC-COO−

    Carboxylic acids

  • 4.2Water, E

    PhCOOH→PhCOO−

    Carboxylic acids

  • 4.6Water, E

    PhNH3+→PhNH2

    Ammonium and cations

    Williams prints 4.19 for aniline.

  • 4.72Water, E, W

    HN3→N3−

    Inorganic acids

  • 4.76Water, E, W

    CH3COOH→CH3COO−

    Carboxylic acids

  • 5.21Water, E

    Pyridine-H+→Pyridine

    Ammonium and cations

    Williams lists 5.14 (thermodynamic).

  • 5.96Water, E

    HONH3+→HONH2

    Ammonium and cations

    Williams: 5.97.

  • 6.3Water, E

    CF3SO2NH2→CF3SO2NH−

    N-H acids

  • 6.35Water, W

    H2CO3→HCO3−

    Inorganic acids

    Apparent value for dissolved CO₂ plus H₂CO₃. Williams also lists 3.58 for true H₂CO₃.

  • 6.95Water, E, W

    Imidazole-H+→Imidazole

    Ammonium and cations

  • 7.0Water, E, W

    H2S→HS−

    Inorganic acids

  • ≈7approximateWater, E

    PhSH→PhS−

    Alcohols, phenols, thiols

    Printed as ≈7. Williams lists 8.20, 7.8 and 6.52 from different studies.

  • 7.1Water, E

    p-O2NC6H4OH→p-O2NC6H4O−

    Alcohols, phenols, thiols

  • 7.21Water, E, W

    H2PO4−→HPO42−

    Inorganic acids

  • 7.21Water, E, W

    HSO3−→SO32−

    Inorganic acids

    Williams prints 7.21 as a thermodynamic value (7.0 in an older entry).

  • 7.5Water, E, W

    HOCl→ClO−

    Inorganic acids

    Williams: 7.53.

  • 7.9DMSO, E, B

    HN3→N3−

    Inorganic acids

  • 8.12Water, E

    N2H5+→N2H4

    Ammonium and cations

    Williams: 8.10.

  • 8.2Water, E, W

    CH3CO3H→CH3CO3−

    Alcohols, phenols, thiols

  • 8.3Water, E

    Phthalimide→Phthalimide anion

    N-H acids

  • 8.95Water, E, W

    CH3COCH2COCH3→CH3COCHCOCH3−

    C-H acids

    Ripin and Evans round this to 9.

  • 9.0DMSO, E

    Et3NH+→Et3N

    Ammonium and cations

  • 9.23Water, E, W

    B(OH)3→B(OH)4−

    Inorganic acids

    Lewis acid: it accepts HO⁻ rather than losing H⁺.

  • 9.24Water, E, W

    NH4+→NH3

    Ammonium and cations

    Ripin and Evans print 9.2; Williams prints 9.24.

  • 9.3Water, E

    (CF3)2CHOH→(CF3)2CHO−

    Alcohols, phenols, thiols

  • 9.4Water, E, W

    HCN→CN−

    Inorganic acids

  • 9.7DMSO, E

    CF3SO2NH2→CF3SO2NH−

    N-H acids

  • 9.8DMSO, E

    Quinuclidine-H+→Quinuclidine

    Ammonium and cations

  • 9.95Water, E

    PhOH→PhO−

    Alcohols, phenols, thiols

  • ≈10approximateWater, E

    CH3NO2→CH2NO2−

    C-H acids

    Printed as ≈10.

  • 10.3DMSO, E

    PhSH→PhS−

    Alcohols, phenols, thiols

  • 10.33Water, W

    HCO3−→CO32−

    Inorganic acids

  • 10.5DMSO, E, B

    NH4+→NH3

    Ammonium and cations

  • 10.6Water, E

    EtNH3+→EtNH2

    Ammonium and cations

  • 10.75Water, E

    Et3NH+→Et3N

    Ammonium and cations

  • 10.8DMSO, E, B

    p-O2NC6H4OH→p-O2NC6H4O−

    Alcohols, phenols, thiols

  • 11.0Water, E

    Quinuclidine-H+→Quinuclidine

    Ammonium and cations

  • 11Water, E

    CH3COCH2CO2Et→CH3COCHCO2Et−

    C-H acids

  • 11.1DMSO, E

    PhCOOH→PhCOO−

    Carboxylic acids

  • 11.1DMSO, E, B

    CH2(CN)2→CH(CN)2−

    C-H acids

  • 11.6Water, E

    H2O2→HOO−

    Inorganic acids

  • 12estimateDMSO, E

    DBU-H+→DBU

    Ammonium and cations

    Printed as "(12) estimate" in the source.

  • 12.3DMSO, E

    CH3COOH→CH3COO−

    Carboxylic acids

  • 12.32Water, E, W

    HPO42−→PO43−

    Inorganic acids

  • 12.5Water, E, W

    CF3CH2OH→CF3CH2O−

    Alcohols, phenols, thiols

  • 12.9DMSO, E, B

    HCN→CN−

    Inorganic acids

  • 12.92Water, W

    HS−→S2−

    Inorganic acids

  • 13Water, E

    CH2(CO2Me)2→CH(CO2Me)2−

    C-H acids

  • 13.3DMSO, E, B

    CH3COCH2COCH3→CH3COCHCOCH3−

    C-H acids

  • 13.9DMSO, E, B

    1,2,3-Triazole→Triazolide

    N-H acids

  • 14.0Water, E, W

    H2O→HO−

    Inorganic acids

    Ripin and Evans (2024) and Williams (14.0*) give 14.0, on the same 1 M scale as the alcohols and phenols here. Many organic textbooks print 15.7 because they divide Kw by 55.5 M; Silverstein and Heller (J. Chem. Educ. 2017) argue that is inconsistent with how other pKa values are defined.

  • 14.2DMSO, E, B

    CH3COCH2CO2Et→CH3COCHCO2Et−

    C-H acids

  • 14.7DMSO, E, B

    Succinimide→Succinimide anion

    N-H acids

  • 15extrapolatedWater, E

    Cyclopentadiene→Cyclopentadienide

    C-H acids

  • 15DMSO, E, B

    HF→F−

    Inorganic acids

  • 15.1extrapolatedWater, E

    CH3CONH2→CH3CONH−

    N-H acids

  • 15.5extrapolatedWater, E, W

    CH3OH→CH3O−

    Alcohols, phenols, thiols

    Williams: 15.54.

  • 15.7DMSO, E, B

    CH2(CO2Me)2→CH(CO2Me)2−

    C-H acids

    Reich-Bordwell prints 15.9 for the dimethyl malonate entry.

  • 16.1DMSO, E

    PhSO2NH2→PhSO2NH−

    N-H acids

  • 16.4DMSO, E, B

    Benzimidazole→Benzimidazolide

    N-H acids

  • 16.5extrapolatedWater, E

    (CH3)2CHOH→(CH3)2CHO−

    Alcohols, phenols, thiols

  • 17.0extrapolatedWater, E

    (CH3)3COH→(CH3)3CO−

    Alcohols, phenols, thiols

  • 17.2DMSO, E, B

    CH3NO2→CH2NO2−

    C-H acids

  • 17.5DMSO, E

    CH3SO2NH2→CH3SO2NH−

    N-H acids

  • 18.0DMSO, E, B

    PhOH→PhO−

    Alcohols, phenols, thiols

  • 18.0DMSO, E, B

    Cyclopentadiene→Cyclopentadienide

    C-H acids

  • 18.2DMSO, E

    (CF3)2CHOH→(CF3)2CHO−

    Alcohols, phenols, thiols

    Reich-Bordwell prints 17.9 (Ripin and Evans: 18.2).

  • 18.6DMSO, E, B

    Imidazole→Imidazolide

    N-H acids

  • 19.8DMSO, E, B

    Pyrazole→Pyrazolide

    N-H acids

    Reich-Bordwell prints 19.9 in the azole block.

  • 20.95DMSO, E, B

    Indole→Indolide

    N-H acids

  • 21.9DMSO, E, B

    PhCH2CN→PhCHCN−

    C-H acids

  • 22.6DMSO, E, B

    Fluorene→Fluorenide

    C-H acids

  • 23.0DMSO, E, B

    Pyrrole→Pyrrolide

    N-H acids

  • 23.3DMSO, E, B

    PhCONH2→PhCONH−

    N-H acids

  • 23.5DMSO, E, B

    CF3CH2OH→CF3CH2O−

    Alcohols, phenols, thiols

  • 24extrapolatedWater, E

    HC≡CH→HC≡C−

    C-H acids

  • 24.7DMSO, E, B

    PhCOCH3→PhCOCH2−

    C-H acids

  • 25.0DMSO, E, B

    Ph2NH→Ph2N−

    N-H acids

  • 25.5DMSO, E, B

    CH3CONH2→CH3CONH−

    N-H acids

  • 26.5DMSO, E, B

    CH3COCH3→CH3COCH2−

    C-H acids

  • 27.9DMSO, E

    CH3OH→CH3O−

    Alcohols, phenols, thiols

    Reich-Bordwell currently prints 29.0 (Ripin and Evans: 27.9).

  • 29.0DMSO, E, B

    PhSO2CH3→PhSO2CH2−

    C-H acids

  • 29.3DMSO, E

    (CH3)2CHOH→(CH3)2CHO−

    Alcohols, phenols, thiols

    Reich-Bordwell currently prints 30.3 (Ripin and Evans: 29.3).

  • 29.4DMSO, E

    (CH3)3COH→(CH3)3CO−

    Alcohols, phenols, thiols

    Reich-Bordwell currently prints 32.2 (Ripin and Evans: 29.4).

  • 30.3DMSO, E, B

    CH3CO2-t-Bu→CH2CO2-t-Bu−

    C-H acids

  • 30.6DMSO, E

    PhNH2→PhNH−

    N-H acids

  • 30.6DMSO, E, B

    Ph3CH→Ph3C−

    C-H acids

  • 31.2DMSO, E

    H2O→HO−

    Inorganic acids

    Ripin and Evans print 31.2 here and 32 in their inorganic section; Reich-Bordwell prints 31.4.

  • 31.3DMSO, E, B

    CH3CN→CH2CN−

    C-H acids

  • 31.5extrapolatedWater, E

    Ph3CH→Ph3C−

    C-H acids

  • 33.5extrapolatedWater, E

    Ph2CH2→Ph2CH−

    C-H acids

  • 35.1extrapolatedDMSO, E, B

    (CH3)2SO→CH3SOCH2−

    C-H acids

  • ≈36approximateWater, E

    H2→H−

    C-H acids

    Printed as ~36.

  • 38extrapolatedWater, E

    NH3→NH2−

    N-H acids

  • 41extrapolatedWater, E

    PhCH3→PhCH2−

    C-H acids

  • 41extrapolatedDMSO, E, B

    NH3→NH2−

    N-H acids

  • 43extrapolatedWater, E

    C6H6→C6H5−

    C-H acids

  • 43extrapolatedDMSO, E

    PhCH3→PhCH2−

    C-H acids

  • 48extrapolatedWater, E

    CH4→CH3−

    C-H acids

  • 56extrapolatedDMSO, E, B

    CH4→CH3−

    C-H acids

Sources: E = Ripin and Evans pKa table (ACS Division of Organic Chemistry, updated 2024-04-16); B = Reich, Bordwell equilibrium pKa table in DMSO (updated 2024-07-26); W = Williams pKa data, compiled by Jencks and Westheimer (updated 2022-04-07). Water values are at 25 °C. Flagged values (below 0, or above 14 in water and above 35 in DMSO) are extrapolated in the source, not measured directly. Print splits the table into pages of 16 rows.

Free pKa Charts

Every chart below is drawn from the same data as the tool above. View, download and print them free, no sign-up.

Water, pKa below 10

pKa Table in Water: Strong and Moderate Acids

Aqueous pKa values below 10, strongest acid first, from triflic acid to phenol.

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Reference tables

Comparison charts

Printable versions

Worked examples

Studying pKa through titrations? See the titration curve guide for how the half-equivalence point gives pKa, or draw one with the titration curve generator.

How to read a pKa table

  • The pKa of an acid HA is the pH at which half of it has lost its proton. It equals −log10 of the acid dissociation constant Ka, so every drop of one unit means the acid is ten times stronger. Hydrochloric acid, with a pKa near −8, gives up its proton far more readily than acetic acid at 4.76, which in turn is far stronger than methanol at 15.5.
  • Each row here pairs the acid with its conjugate base, the species left after the proton leaves. The weaker the acid, the stronger and more reactive its conjugate base. That is why chloride is inert in water while methoxide, the conjugate base of a pKa 15.5 acid, deprotonates many organic compounds.

Why water and DMSO values differ

Water stabilizes small anions through hydrogen bonds, so acids that release an anion look strong in it. DMSO is a polar solvent that cannot donate hydrogen bonds. In DMSO, acetic acid rises from 4.76 to 12.3 and phenol from 9.95 to 18.0, while ammonium and triethylammonium barely move because they release a neutral base. Most organic carbon acids were measured in DMSO, where the pKa range reaches the mid-30s, because water cannot show acids weaker than about 14. Never subtract a water value from a DMSO value. The deprotonation check on this page only compares two values from the same solvent.

Using pKa to predict the direction of a reaction

For HA + B⁻ ⇌ A⁻ + HB, the equilibrium constant is K = 10^(pKa of HB − pKa of HA). A base can deprotonate an acid when the conjugate acid of the base has a higher pKa than the acid itself. A gap of three units or more means the reaction is close to complete, a gap of one unit gives about ten to one in favor of products, and a gap near zero leaves a mixture. For example, tert-butoxide deprotonates acetone in DMSO: with the Ripin and Evans values (tert-butanol 29.4, acetone 26.5) ΔpKa is +2.9 and K is near 800, and the newer Reich-Bordwell value for tert-butanol (32.2) makes the gap larger still. Either way the ketone is converted to its enolate. A hydroxide ion in water is a different case: with pKa 14.0 for water, it cannot fully deprotonate methanol (15.5), and ΔpKa is −1.5. Real reactions also depend on concentration, ion pairing and temperature, so use ΔpKa as a guide.

pKa and the titration curve

At the half-equivalence point of a weak acid titration, half the acid has been converted to its conjugate base, so pH equals pKa. Reading the flat buffer region of a titration curve is the standard way to measure a pKa in the lab. Polyprotic acids such as phosphoric acid show one half-equivalence point per proton, which is why H3PO4 has three rows here, at 2.12, 7.21 and 12.32.

Where the values come from and what is flagged

Every row names its source: the Ripin and Evans table and the Reich-Bordwell DMSO table, both hosted by the ACS Division of Organic Chemistry, and the Williams compilation by Jencks and Westheimer for aqueous values. Values below 0, above 14 in water and above 35 in DMSO are extrapolated in the source, not measured, and are flagged on every row. Where sources disagree, the row notes the other value. The pKa of water itself is the best-known case: this page uses 14.0 (and 0.0 for H3O⁺) from the 2024 Ripin and Evans table, on the same 1 M scale as the alcohol and phenol values, while many organic textbooks print 15.7 and −1.74.

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