Everything about Ph totally explained
pH is the measure of the
acidity or
basicity of a
solution. It is formally a measure of the
activity of dissolved
hydrogen ions (H
+), but for very dilute solutions, the
molarity (
molar concentration) of H
+ may be used as a substitute with little loss of accuracy. In solution, hydrogen ions occur as a number of
cations including
hydronium ions (H
3O
+).
In pure water at 25°C, the concentration of H
+ equals the concentration of
hydroxide ions (OH
-). This is defined as "neutral" and corresponds to a pH level of 7.0. Solutions in which the concentration of H
+ exceeds that of OH
- have a pH value lower than 7.0 and are known as acids. Solutions in which OH
- exceeds H
+ have a pH value greater than 7.0 and are known as bases. Because pH is dependent on ionic activity, a property which can't be measured easily or fully predicted theoretically, it's difficult to determine an accurate value for the pH of a solution. The pH reading of a solution is usually obtained by comparing unknown solutions to those of known pH, and there are
several ways to do so.
The concept of pH was first introduced by
Danish chemist S. P. L. Sørensen at the
Carlsberg Laboratory in
1909. The name pH has been claimed to have come from any of several sources including:
pondus hydrogenii,
potentia hydrogenii (
Latin),
potentiel hydrogène (
French), and
potential of hydrogen (
English).
Definition
The
operational definition of pH is officially defined by International Standard
ISO 31-8 as follows: For a solution X, first measure the
electromotive force EX of the
galvanic cell » reference electrode | concentrated solution of KCl || solution X | H
2 | Pt
and then also measure the electromotive force
ES of a galvanic cell that differs from the above one only by the replacement of the solution X of unknown pH, pH(X), by a solution S of a known standard pH, pH(S). The pH of X is then
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