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[c] [2] For example, a hypothetical weak acid having K a = 10 −5, the value of log K a is the exponent (−5), giving pK a = 5. For acetic acid, K a = 1.8 x 10 −5, so pK a is 4.7. A higher K a corresponds to a stronger acid (an acid that is more dissociated at equilibrium).
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 ...
The converse is true in a basic medium. For example, Naproxen is a non-steroidal anti-inflammatory drug that is a weak acid (its pKa value is 5.0). The gastric juice has a pH of 2.0. It is a three-fold difference (due to log scale) between its pH and its pKa; therefore there is a 1000× difference between the charged and uncharged concentrations.
Such a statement is incorrect. For example, acetic acid is a weak acid which has a = 1.75 x 10 −5. Its conjugate base is the acetate ion with K b = 10 −14 /K a = 5.7 x 10 −10 (from the relationship K a × K b = 10 −14), which certainly does not correspond to a strong base
In chemistry and biochemistry, the Henderson–Hasselbalch equation = + ([] []) relates the pH of a chemical solution of a weak acid to the numerical value of the acid dissociation constant, K a, of acid and the ratio of the concentrations, [] [] of the acid and its conjugate base in an equilibrium.
For example, if a macromolecule M has three binding sites, K′ 1 describes a ligand being bound to any of the three binding sites. In this example, K′ 2 describes two molecules being bound and K′ 3 three molecules being bound to the macromolecule. The microscopic or individual dissociation constant describes the equilibrium of ligands ...
Buffer capacity falls to 33% of the maximum value at pH = pK a ± 1, to 10% at pH = pK a ± 1.5 and to 1% at pH = pK a ± 2. For this reason the most useful range is approximately pK a ± 1. When choosing a buffer for use at a specific pH, it should have a pK a value as close as possible to that pH. [2]
At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two pK a values) the dihydrogen phosphate ion, [H 2 PO 4] −, is practically the only species present. Around pH 9.8 (mid-way between the second and third pK a values) the monohydrogen phosphate ion, [HPO 4] 2−, is the only species ...