E5: Acid Dissociation Constants of Organics
- Page ID
- 6647
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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 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
\[K_a \times K_b = K_w\]
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 |  |
4.42 5.42 | 3.8×10–5 3.8×10–6 | |
| alanine |  |
2.348 (COOH) 9.867 (NH3) | 4.49×10–3 1.36×10–10 | |
| aminobenzene |  |
4.601 | 2.51×10–5 | |
| 4-aminobenzene sulfonic acid |  |
3.232 | 5.86×10–4 | |
| 2-aminobenozic acid |  |
2.08 (COOH) 4.96 (NH3) | 8.3×10–3 1.1×10–5 | |
| 2-aminophenol (T = 20 oC) |  |
4.78 (NH3) 9.97 (OH) | 1.7×10–5 1.05×10–10 | |
| ammonia | NH4+ | 9.244 | 5.70×10–10 | |
| arginine |  |
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) |  |
2.14 (COOH) 8.72 (NH3) |
7.2×10–3 1.9×10–9 |
|
| asparatic acid |  |
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 |  |
4.202 | 6.28×10–5 | |
| benzylamine |  |
9.35 | 4.5×10–10 | |
| boric acid (pKa2, pKa3:T = 20 oC) | 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 |  |
9.40 12.8 |
4.0×10–10 1.6×10–13 |
|
| chloroacetic acid | ClCH2COOH | 2.865 | 1.36×10–3 | |
| chromic acid (pKa1:T = 20 oC) | H2CrO4 | -0.2 6.51 |
1.6 3.1×10–7 |
|
| citric acid |  |
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) |  |
4.16 | 6.9×10–5 | |
| cysteine |  |
[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)2NH2+ | 10.933 | 1.17×10–11 | |
| dimethylamine | (CH3)2NH2+ | 10.774 | 1.68×10–11 | |
| dimethylglyoxime |  |
10.66 12.0 |
2.2×10–11 1.×10–12 |
|
| ethylamine | CH3CH2NH3+ | 10.636 | 2.31×10–11 | |
| ethylenediamine | +H3NCH2CH2NH3+ | 6.848 9.928 |
1.42×10–7 1.18×10–10 |
|
| ethylenediaminetetraacetic acid (EDTA) (μ = 0.1 M) |
 |
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 |  |
3.053 4.494 |
8.85×10–4 3.21×10–5 |
|
| glutamic acid |  |
2.33 (α-COOH) 4.42 (λ-COOH) 9.95 (NH3) |
5.9×10–3 3.8×10–5 1.12×10–10 |
|
| glutamine (μ = 0.1 M) |  |
2.17 (COOH) 9.01 (NH3) |
6.8×10–3 9.8×10–10 |
|
| glycine +H3NCH2COOH |  |
2.350 (COOH) 9.778 (NH3) |
4.47×10–3 1.67×10–10 |
|
| glycolic acid | HOOCH2COOH | 3.831 (COOH) | 1.48×10–4 | |
| histidine (μ = 0.1 M) |  |
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 fluoride | 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 |  |
4.91 (NH) 9.81 (OH) |
1.2×10–5 1.6×10–10 |
|
| hydroxylamine | HONH3+ | 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 |  |
2.319 (COOH) 9.754 (NH3) |
4.80×10–3 1.76×10–10 |
|
| leucine |  |
2.329 (COOH) 9.747 (NH3) |
4.69×10–3 1.79×10–10 |
|
| lysine (μ = 0.1 M) |  |
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 |  |
1.910 6.332 |
9.1×10–3 9.1×10–3 |
|
| malic acid |  |
3.459 (COOH) 5.097 (COOH) |
9.1×10–3 9.1×10–3 |
|
| malonic acid | HOOCCH2COOH | 2.847 5.696 |
9.1×10–3 9.1×10–3 |
|
| methionine (μ = 0.1 M) |  |
2.20 (COOH) 9.05 (NH3) |
9.1×10–3 9.1×10–3 |
|
| methylamine | CH3NH3+ | 10.64 | 9.1×10–3 | |
| 2-methylanaline |  |
4.447 | 9.1×10–3 | |
| 4-methylanaline |  |
5.084 | 9.1×10–3 | |
| 2-methylphenol |  |
10.28 | 9.1×10–3 | |
| 4-methylphenol |  |
10.26 | 9.1×10–3 | |
| nitrilotriacetic acid (T = 20 oC) (pKa1: μ = 0.1 m) |
 |
1.1 (COOH) 1.650 (COOH) 2.940 (COOH) 10.334 (NH3) |
9.1×10–3 9.1×10–3 9.1×10–3 9.1×10–3 |
|
| 2-nitrobenzoic acid |  |
2.179 | 9.1×10–3 | |
| 3-nitrobenzoic acid |  |
3.449 | 9.1×10–3 | |
| 4-nitrobenzoic acid |  |
3.442 | 3.61×10–4 | |
| 2-nitrophenol |  |
7.21 | 6.2×10–8 | |
| 3-nitrophenol |  |
8.39 | 4.1×10–9 | |
| 4-nitrophenol |  |
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 5.42×10–5 |
|
| 1,10-phenanthroline |  |
4.86 | 1.38×10–5 | |
| phenol |  |
9.98 | 1.05×10–10 | |
| phenylalanine |  |
2.20 (COOH) 9.31 (NH3) |
6.3×10–3 4.9×10–10 |
|
| phosphoric acid | H3PO4 | 2.148 7.199 12.35 |
7.11×10–3 6.32×10–8 4.5×10–13 |
|
| phthalic acid |  |
2.950 5.408 |
1.12×10–3 3.91×10–6 |
|
| piperdine |  |
11.123 | 7.53×10–12 | |
| proline |  |
1.952 (COOH) 10.640 (NH) |
1.12×10–2 2.29×10–11 |
|
| propanoic acid | CH3CH2COOH | 4.874 | 1.34×10–5 | |
| propylamine | CH3CH2CH2NH3+ | 10.566 | 2.72×10–11 | |
| pryidine |  |
5.229 | 5.90×10–6 | |
| resorcinol |  |
9.30 11.06 |
5.0×10–10 8.7×10–12 |
|
| salicylic acid |  |
2.97 (COOH) 13.74 (OH) |
1.1×10–3 1.8×10–14 |
|
| serine |  |
2.187 (COOH) 9.209 (NH3) |
6.50×10–3 6.18×10–10 |
|
| succinic acid |  |
4.207 5.636 |
6.21×10–5 2.31×10–6 |
|
| sulfuric acid | H2SO4 | strong 1.99 |
— 1.0×10–2 |
|
| sulfurous acid | H2SO3 | 1.91 7.18 |
1.2×10–2 6.6×10–8 |
|
| D-tartaric acid |  |
3.036 (COOH) 4.366 (COOH) |
9.20×10–4 4.31×10–5 |
|
| threonine |  |
2.088 (COOH) 9.100 (NH3) |
8.17×10–3 7.94×10–10 |
|
| thiosulfuric acid | H2S2O3 | 0.6 1.6 |
3.×10–1 3.×10–2 |
|
| trichloroacetic acid (μ = 0.1 M) | Cl3CCOOH | 0.66 | 2.2×10–1 | |
| triethanolamine | (HOCH2CH2)3NH+ | 7.762 | 1.73×10–8 | |
| triethylamine | (CH3CH2)3NH+ | 10.715 | 1.93×10–11 | |
| trimethylamine | (CH3)3NH+ | 9.800 | 1.58×10–10 | |
| tris(hydroxymethyl)amino methane (TRIS or THAM) | (HOCH2)3CNH3+ | 8.075 | 8.41×10–9 | |
| tryptophan (μ = 0.1 M) |  |
2.35 (COOH) 9.33 (NH3) |
4.5×10–3 4.7×10–10 |
|
| tryosine (pKa1: μ = 0.1 M) |  |
2.17 (COOH) 9.19 (NH3) 10.47 (OH) |
6.8×10–3 6.5×10–10 3.4×10–11 |
|
| valine |  |
2.286 (COOH) 9.718 (NH3) |
5.18×10–3 1.91×10–10 |
|