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An acidity function is a measure of the acidity of a medium or solvent system, [1] [2] usually expressed in terms of its ability to donate protons to (or accept protons from) a solute (Brønsted acidity). The pH scale is by far the most commonly used acidity function, and is ideal for dilute aqueous solutions.
The relative concentration of undissociated acid is shown in blue, and of its conjugate base in red. The pH changes relatively slowly in the buffer region, pH = pK a ± 1, centered at pH = 4.7, where [HA] = [A −]. The hydrogen ion concentration decreases by less than the amount expected because most of the added hydroxide ion is consumed in ...
Bases are proton acceptors; a base will receive a hydrogen ion from water, H 2 O, and the remaining H + concentration in the solution determines pH. A weak base will have a higher H + concentration than a stronger base because it is less completely protonated than a stronger base and, therefore, more hydrogen ions remain in its solution.
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. [10] 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. [10]
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.
The Charlot equation, named after Gaston Charlot, is used in analytical chemistry to relate the hydrogen ion concentration, and therefore the pH, with the formal analytical concentration of an acid and its conjugate base. It can be used for computing the pH of buffer solutions when the approximations of the Henderson–Hasselbalch equation ...
In particular, the pH of a solution can be predicted when the analytical concentration and pK a values of all acids and bases are known; conversely, it is possible to calculate the equilibrium concentration of the acids and bases in solution when the pH is known. These calculations find application in many different areas of chemistry, biology ...
In biochemistry and in biological fluids, at pH = 7, it is thus important to note that the reduction potential of the protons ( H +) into hydrogen gas H 2 is no longer zero as with the standard hydrogen electrode (SHE) at 1 M H + (pH = 0) in classical electrochemistry, but that E red = − 0.414 V {\displaystyle E_{\text{red}}=-0.414\mathrm {V ...