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Well measured values are typically within 0.1 units of each other. Data presented here were taken at 25 °C in water. [7] [86] More values can be found in the Thermodynamics section, above. A table of pK a of carbon acids, measured in DMSO, can be found on the page on carbanions.
See Amino acid for the pK a values of all amino acid side chains inferred in such a way. There are also numerous experimental studies that have yielded such values, for example by use of NMR spectroscopy. The table below lists the model pK a values that are often used in a protein pK a calculation, and contains a third column based on protein ...
Acid strength is the tendency of an acid, symbolised by the chemical formula, to dissociate into a proton, +, and an anion, .The dissociation or ionization of a strong acid in solution is effectively complete, except in its most concentrated solutions.
In the case of multiple pK values they are designated by indices: pK 1, pK 2, pK 3 and so on. For amino acids, the pK 1 constant refers to its carboxyl (–COOH) group, pK 2 refers to its amino (–NH 2) group and the pK 3 is the pK value of its side chain.
The following table presents pK a values at 20 °C. Values change by about 0.01 per degree of temperature. [1] [3] Good's original 1966 paper had two older buffers (marked with italics) for comparison. In 1972 Good published a second list with three more buffers, and five more were added in 1980.
Oxalic acid's pK a values vary in the literature from 1.25 to 1.46 and from 3.81 to 4.40. [ 25 ] [ 26 ] [ 27 ] The 100th ed of the CRC, released in 2019, has values of 1.25 and 3.81. [ 28 ] Oxalic acid is relatively strong compared to other carboxylic acids :
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The difference between successive pK a values is sufficiently large so that salts of either monohydrogen phosphate, HPO 2− 4 or dihydrogen phosphate, H 2 PO − 4, can be prepared from a solution of phosphoric acid by adjusting the pH to be mid-way between the respective pK a values.