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Nitric acid, with a pK value of around −1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. [23] At lower pH values it behaves as a weak acid. pK a values for strong acids have been estimated by theoretical means. [24] For example, the pK a value of aqueous HCl has been estimated as −9.3.
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]
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.
This usage is consistent with the common parlance of most practicing chemists.) When the acidic medium in question is a dilute aqueous solution, the H 0 {\displaystyle H_{0}} is approximately equal to the pH value, which is a negative logarithm of the concentration of aqueous H + {\displaystyle {\ce {H+}}} in solution.
In chemistry, biochemistry, and pharmacology, a dissociation constant (K D) is a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions.
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 ...
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 pKa of KHP is 5.4, so its pH buffering range would be 4.4 to 6.4; however, due to the presence of the second acidic group that bears the potassium ion, the first pKa also contributes to the buffering range well below pH 4.0, which is why KHP is a good choice for use as a reference standard for pH 4.00. [8] [9]