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Chemistry LibreTexts

16.11: Acid Dissociation Constants

  2. Last updated
    Jun 15, 2024
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The following table provides pKa and Ka values for selected weak acids. All values are from Martell, A. E.; Smith, R. M. Critical Stability Constants, Vols. 1–4. Plenum Press: New York, 1976. Unless otherwise stated, values are for 25 oC and for zero ionic strength. Those values in brackets are considered less reliable.

Weak acids are arranged alphabetically by the names of the neutral compounds from which they are derived. In some cases—such as acetic acid—the compound is the weak acid. In other cases—such as for the ammonium ion—the neutral compound is the conjugate base. Chemical formulas or structural formulas are shown for the fully protonated weak acid. Successive acid dissociation constants are provided for polyprotic weak acids; where there is ambiguity, the specific acidic proton is identified.

To find the Kb value for a conjugate weak base, recall that

Ka×Kb=Kw

for a conjugate weak acid, HA, and its conjugate weak base, A–.

compound conjugate acid pKa Ka
acetic acid CH3COOH 4.757 1.75×10−5
adipic acid
adipic.png

4.42

5.42

3.8×10−5

3.8×10−6
alanine alanine.png

2.348 (COOH)

9.867 (NH3)

4.49×10−3

1.36×10−10
aminobenzene aminobenzene.png 4.601 2.51×10−5
4-aminobenzene sulfonic acid aminobenzenesulfonic.png 3.232 5.86×10−4
2-aminobenzoic acid
2aminobenzoic.png

2.08 (COOH)

4.96 (NH3)

8.3×10−3

1.1×10−5
2-aminophenol (T=20°C) 2aminophenol.png

4.78 (NH3)

9.97 (OH)

1.7×10−5

1.05×10−10
ammonia NH+4 9.244 5.70×10−10
arginine
arginine.png

1.823 (COOH)

8.991 (NH3)

[12.48] (NH2)

1.50×10−2

1.02×10−9

[3.3×10−13]
arsenic acid H3AsO4

2.24

6.96

11.50

5.8×10−3

1.1×10−7

3.2×10−12
asparagine (μ=0.1 M) asparagine.png

2.14 (COOH)

8.72 (NH3)

7.2×10−3

1.9×10−9
aspartic acid aspartic.png

1.990 (α-COOH)

3.900 (β-COOH)

10.002 (NH3)

1.02×10−2

1.26×10−4

9.95×10−11
benzoic acid benzoic.png 4.202 6.28×10−5
benzylamine benzylamine.png 9.35 4.5×10−10
boric acid (pKa2,pKa3: T=20°C) H3BO3

9.236

[12.74]

[13.80]

5.81×10−10

[1.82×10−13]

[1.58×10−14]
carbonic acid H2CO3

6.352

10.329

4.45×10−7

4.69×10−11
catechol catechol.png

9.40

12.8

4.0×10−10

1.6×10−13
chloracetic acid ClCH2COOH 2.865 1.36×10−3
chromic acid (pKa1: T=20°C) H2CrO4

–0.2

6.51

1.6

3.1×10−7
citric acid citric.png

3.128 (COOH)

4.761 (COOH)

6.396 (COOH)

7.45×10−4

1.73×10−5

4.02×10−7
cupferron (μ=0.1 M) cupferron.png 4.16 6.9×10−5
cysteine cysteine.png

[1.71] (COOH)

8.36 (SH)

10.77 (NH3)

[1.9×10−2]

4.4×10−9

1.7×10−11
dichloracetic acid Cl2CHCOOH 1.30 5.0×10−2
diethylamine (CH3CH2)2NH+2 10.933 1.17×10−11
dimethylamine (CH3)2NH+2 10.774 1.68×10−11
dimethylglyoxime dimethylglyoxime.png

10.66

12.0

2.2×10−11

1.×10−12
ethylamine CH3CH2NH+3 10.636 2.31×10−11
ethylenediamine +H3NCH2CH2NH+3

6.848

9.928

1.42×10−7

1.18×10−10

ethylenediaminetetracetic acid

(EDTA) (μ=0.1 M)

 EDTA.png

0.0 (COOH)

1.5 (COOH)

2.0 (COOH)

2.66 (COOH)

6.16 (NH)

10.24 (NH)

1.0

3.2×10−2

1.0×10−2

2.2×10−3

6.9×10−7

5.8×10−11
formic acid HCOOH 3.745 1.80×10−4
fumaric acid fumaric.png

3.053

4.494

8.85×10−4

3.21×10−5
glutamic acid
glutamic.png

2.33 (α-COOH)

4.42 (λ-COOH)

9.95 (NH3)

5.9×10−3

3.8×10−5

1.12×10−10
glutamine glutamine.png

2.17 (COOH)

9.01 (NH3)

6.8×10−3

9.8×10−10
glycine glycine.png

2.350 (COOH)

9.778 (NH3)

4.47×10−3

1.67×10−10
glycolic acid HOOCH2COOH

3.881 (COOH)

 1.48×10−4
histidine (μ=0.1 M) histidine.png

1.7 (COOH)

6.02 (NH)

9.08 (NH3)

2.×10−2

9.5×10−7

8.3×10−10
hydrogen cyanide HCN 9.21 6.2×10−10
hydrogen fluroride HF 3.17 6.8×10−4
hydrogen peroxide H2O2 11.65 2.2×10−12
hydrogen sulfide H2S

7.02

13.9

9.5×10−8

1.3×10−14
hydrogen thiocyanate HSCN 0.9 1.3×10−1
8-hydroxyquinoline hydroxyquinoline.png

4.9 (NH)

9.81 (OH)

1.2×10−5

1.6×10−10
hydroxylamine HONH+3 5.96 1.1×10−6
hypobromous acid HOBr 8.63 2.3×10−9
hypochlorous acid HOCl 7.53 3.0×10−8
hypoiodous acid HOI 10.64 2.3×10−11
iodic acid HIO3 0.77 1.7×10−1
isoleucine
isoleucine.png

2.319 (COOH)

9.754 (NH3)

4.8×10−3

1.76×10−10
leucine leucine.png

2.329 (COOH)

9.747 (NH3)

4.69×10−3

1.79×10−10
lysine (μ=0.1 M) lysine.png

2.04 (COOH)

9.08 (α-NH3)

10.69 (ϵ-NH3)

9.1×10−3

8.3×10−10

2.0×10−11
maleic acid maleic.png

1.910

6.332

1.23×10−2

4.66×10−7
malic acid malic.png

3.459 (COOH)

5.097 (COOH)

3.48×10−4

8.00×10−6
malonic acid HOOCCH2COOH

2.847

5.696

1.42×10−3

2.01×10−6
methionine (μ=0.1 M) methionine.png

2.20 (COOH)

9.05 (NH3)

6.3×10−3

8.9×10−10
methylamine CH3NH+3 10.64 2.3×10−11
2-methylanaline methylaniline2.png 4.447 3.57×10−5
4-methylanaline methylaniline4.png 5.084 8.24×10−6
2-methylphenol methylphenol2.png 10.28 5.2×10−11
4-methylphenol methylphenol4.png 10.26 5.5×10−11

nitrilotriacetic acid

(T=20°C),pKa1: μ=0.1 M)

 nitriloacetic.png

1.1 (COOH)

1.650 (COOH)

2.940 (COOH)

10.334 (NH3)

8.×10−2

2.24×10−2

1.15×10−3

4.63×10−11
2-nitrobenzoic acid nitrobenzoic2.png 2.179 6.62×10−3
3-nitrobenzoic acid nitrobenzoic3.png 3.449 3.56×10−4
4-nitrobenzoic acid nitrobenzoic4.png 3.442 3.61×10−4
2-nitrophenol nitrophenol2.png 7.21 6.2×10−8
3-nitrophenol
nitrophenol3.png		 8.39 4.1×10−9
4-nitrophenol nitrophenol4.png 7.15 7.1×10−8
nitrous acid HNO2 3.15 7.1×10−4
oxalic acid H2C2O4

1.252

4.266

5.60×10−2

5.42 \times 10^{-5}
1,10-phenanthroline phenanthroline.png 4.86 1.38 \times 10^{-5}
phenol phenol.png 9.98 1.05 \times 10^{-10}
phenylalanine phenylalanine.png

2.20 (COOH)

9.31 (\ce{NH3})

6.3 \times 10^{-3}

4.9 \times 10^{-10}
phosphoric acid \ce{H3PO4}

2.148

7.199

12.35

7.11 \times 10^{-3}

6.32 \times 10^{-8}

4.5 \times 10^{-13}
phthalic acid phthalic.png

2.950

5.408

1.12 \times 10^{-3}

3.91 \times 10^{-6}
piperdine piperdine.png 11.123 7.53 \times 10^{-12}
proline proline.png

1.952 (COOH)

10.650 (NH)

1.12 \times 10^{-2}

2.29 \times 10^{-11}
propanoic acid \ce{CH3CH2COOH}

4.874

 1.34 \times 10^{-5}
propylamine \ce{CH3CH2CH2NH3+} 10.566 2.72 \times 10^{-11}
pyridine pyridine.png 5.229 5.90 \times 10^{-6}
resorcinol resorcinal.png

9.30

11.06

5.0 \times 10^{-10}

8.7 \times 10^{-12}
salicylic acid salicylic.png

2.97 (COOH)

13.74 (OH)

1.1 \times 10^{-3}

1.8 \times 10^{-14}
serine serine.png

2.187 (COOH)

9.209 (\ce{NH3})

6.50 \times 10^{-3}

6.18 \times 10^{-10}
succinic acid succinic.png

4.207

5.636

6.21 \times 10^{-5}

2.31 \times 10^{-6}
sulfuric acid \ce{H2SO4}

strong

1.99

—

1.0 \times 10^{-2}
sulfurous acid \ce{H2SO3}

1.91

7.18

1.2 \times 10^{-2}

6.6 \times 10^{-8}
D-tartaric acid tartaric.png

3.036 (COOH)

4.366 (COOH)

9.20 \times 10^{-4}

4.31 \times 10^{-5}
threonine threoline.png

2.088 (COOH)

9.100 (\ce{NH3})

8.17 \times 10^{-3}

7.94 \times 10^{-10}
thiosulfuric acid \ce{H2S2O3}

0.6

1.6

3. \times 10^{-1}

3. \times 10^{-2}
trichloracetic acid (\mu = 0.1 \text{ M}) \ce{Cl3CCOOH} 0.66 2.2 \times 10^{-1}
triethanolamine \ce{(HOCH2CH2)3NH+} 7.762 1.73 \times 10^{-8}
triethylamine \ce{(CH3CH2)3NH+} 10.715 1.93 \times 10^{-11}
trimethylamine \ce{(CH3)3NH+} 9.800 1.58 \times 10^{-10}
tris(hydroxymethyl)amino methane (TRIS or THAM) \ce{(HOCH2)3CNH3+} 8.075 8.41 \times 10^{-9}
tryptophan (\mu = 0.1 \text{ M})
tryptophan.png

2.35 (COOH)

9.33 (\ce{NH3})

4.5 \times 10^{-3}

4.7 \times 10^{-10}
tyrosine (pK_\text{a1: } \mu = 0.1 \text{ M}) tyrosine.png

2.17 (COOH)

9.19 (\ce{NH3})

10.47 (OH)

6.8 \times 10^{-3}

6.5 \times 10^{-10}

3.4 \times 10^{-11}
valine valine.png

2.286 (COOH)

9.718 (\ce{NH3})

5.18 \times 10^{-3}

1.91 \times 10^{-10}

16.11: Acid Dissociation Constants is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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