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The Henderson-Hasselbalch equation can be used to model these equilibria. It is important to maintain this pH of 7.4 to ensure enzymes are able to work optimally. [12] Life threatening Acidosis (a low blood pH resulting in nausea, headaches, and even coma, and convulsions) is due to a lack of functioning of enzymes at a low pH. [13]
A strong acid, such as hydrochloric acid, at concentration 1 mol dm −3 has a pH of 0, while a strong alkali like sodium hydroxide, at the same concentration, has a pH of 14. Since pH is a logarithmic scale, a difference of one in pH is equivalent to a tenfold difference in hydrogen ion concentration.
A weak acid may be defined as an acid with pK a greater than about −2. An acid with pK a = −2 would be 99 % dissociated at pH 0, that is, in a 1 M HCl solution. Any acid with a pK a less than about −2 is said to be a strong acid. Strong acids are said to be fully dissociated.
The solution is then titrated with a strong base until all the protons have been removed. At each point in the titration pH is measured using a glass electrode and a pH meter. The equilibrium constants are found by fitting calculated pH values to the observed values, using the method of least squares. [59]
In the case of citric acid, the overlap is extensive and solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5. Calculation of the pH with a polyprotic acid requires a speciation calculation to be performed. In the case of citric acid, this entails the solution of the two equations of mass balance:
The pH-dependence of the activity displayed by enzymes and the pH-dependence of protein stability, for example, are properties that are determined by the pK a values of amino acid side chains. The p K a values of an amino acid side chain in solution is typically inferred from the p K a values of model compounds (compounds that are similar to ...
As calculated by the Henderson–Hasselbalch equation, in order to maintain a normal pH of 7.4 in the blood (whereby the pK a of carbonic acid is 6.1 at physiological temperature), a 20:1 ratio of bicarbonate to carbonic acid must constantly be maintained; this homeostasis is mainly mediated by pH sensors in the medulla oblongata of the brain ...
The Hammett acidity function (H 0) is a measure of acidity that is used for very concentrated solutions of strong acids, including superacids.It was proposed by the physical organic chemist Louis Plack Hammett [1] [2] and is the best-known acidity function used to extend the measure of Brønsted–Lowry acidity beyond the dilute aqueous solutions for which the pH scale is useful.