pH

In 1909, the Danish chemist Søren Peter Lauritz Sørensen introduced the concept of pH at the Carlsberg Laboratory,[4] originally using the notation "pH•", with H• as a subscript to the lowercase p. The concept was later revised in 1924 to the modern pH to accommodate definitions and measurements in terms of electrochemical cells.For the sign p, I propose the name 'hydrogen ion exponent' and the symbol pH•.

[5][6] Sørensen described a way of measuring pH using potential differences, and it represents the negative power of 10 in the concentration of hydrogen ions.

[12] She said:In these studies [of bacterial metabolism] Dr. Clark's attention was directed to the effect of acid on the growth of bacteria.

[12]The first electronic method for measuring pH was invented by Arnold Orville Beckman, a professor at the California Institute of Technology in 1934.

[13] It was in response to a request from the local citrus grower Sunkist, which wanted a better method for quickly testing the pH of lemons they were picking from their nearby orchards.

Firstly, the cell is filled with a solution of known hydrogen ion activity and the electromotive force, ES, is measured.

It is calibrated against Buffer solutions of known hydrogen ion (H+) activity proposed by the International Union of Pure and Applied Chemistry (IUPAC).

[3] Two or more buffer solutions are used in order to accommodate the fact that the "slope" may differ slightly from ideal.

Commercial standard buffer solutions usually come with information on the value at 25 °C and a correction factor to be applied for other temperatures.

More correctly, the thermodynamic activity of H+ in dilute solution should be replaced by [H+]/c0, where the standard state concentration c0 = 1 mol/L.

[19] This procedure makes the activity of hydrogen ions equal to the numerical value of concentration.

is its chemical potential in the chosen standard state, R is the molar gas constant and T is the thermodynamic temperature.

[23] The advantages of the unified absolute pH scale include consistency, accuracy, and applicability to a wide range of sample types.

Topsoil pH is influenced by soil parent material, erosional effects, climate and vegetation.

A recent map[28] of topsoil pH in Europe shows the alkaline soils in Mediterranean, Hungary, East Romania, North France.

Because of the relative unimportance of the fluoride ion, the total and seawater scales differ only very slightly.

As part of its operational definition of the pH scale, the IUPAC defines a series of Buffer solutions across a range of pH values (often denoted with National Bureau of Standards (NBS) or National Institute of Standards and Technology (NIST) designation).

To resolve this problem, an alternative series of buffers based on artificial seawater was developed.

Resulting in the following expression for [H+]SWS: However, the advantage of considering this additional complexity is dependent upon the abundance of fluoride in the medium.

In seawater, for instance, sulfate ions occur at much greater concentrations (> 400 times) than those of fluoride.

[36] The pH also influences the Maillard reaction, which is responsible for the browning of food during cooking, impacting both flavor and appearance.

Acidosis, defined by blood pH below 7.35, is the most common disorder of acid–base homeostasis and occurs when there is an excess of acid in the body.

Plaque formation in teeth can create a local acidic environment that results in tooth decay through demineralization.

Strong acids and bases are compounds that are almost completely dissociated in water, which simplifies the calculation.

This equilibrium needs to be taken into account at high pH and when the solute concentration is extremely low.

However, self-ionization of water must also be considered when concentrations of a strong acid or base is very low or high.

In such cases, the system can be treated as a mixture of the acid or base and water, which is an amphoteric substance.

Electrical charges are omitted from subsequent equations for the sake of generality and its value is assumed to have been determined by experiment.

This procedure is illustrated in an ICE table which can also be used to calculate the pH when some additional (strong) acid or alkaline has been added to the system, that is, when CA ≠ CH.

The calculation of hydrogen ion concentrations, using this approach, is a key element in the determination of equilibrium constants by potentiometric titration.