- ISO 31-8
ISO 31-8 is the part of
international standard ISO 31that defines names and symbols for quantities and units related to " physical chemistryand molecular physics".
Quantities and units
In the tables of quantities and their units, the ISO 31-8 standard shows symbols for substances as subscripts (e.g., "c"B, "w"B, "p"B). It also notes that it is generally advisable to put symbols for substances and their states in parentheses on the same line, as in "c"(H2SO4).
Annex A: Names and symbols of the chemical elements
This annex contains a
list of elements by atomic number, giving the names and standard symbols of the chemical elements from atomic number 1 ( hydrogen, H) to 109 ( unnilennium, Une).
The list given in ISO 31-8:1992 was quoted from the 1998
IUPAC"Green Book" Quantities, Units and Symbols in Physical Chemistryand adds in some cases in parentheses the Latin name for information, where the standard symbol has no relation to the English name of the element. Since the 1992 edition of the standard was published, some elements with atomic number above 103 have been discovered and renamed.
Annex B: Symbols for chemical elements and nucleides
Symbols for chemical elements shall be written in roman (upright) type. The symbol is not followed by a full-stop.
Examples:: H He C Ca
Attached subscripts or superscripts specifying a nucleotide or molecule have the following meanings and positions:
nucleon number( mass number) is shown in the left superscriptposition (e.g., 14N)
*The number of atoms of a
nucleotideis shown in the right subscriptposition (e.g., 14N2)
proton number(atomic number) may be indicated in the left subscript position (e.g., 64Gd)
*If necessary, a state of
ionizationor an excited statemay be indicated in the right superscript position (e.g., state of ionization Na+)
Annex C: pH
pHis defined operationally as follows. For a solution X, first measure the electromotive force"E"X of the galvanic cell
:reference electrode | concentrated solution of KCl | solution X | H2 | Pt
and then also measure the electromotive force "E"S 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). Then obtain the pH of X as:pH(X) = pH(S) + ("E"S − "E"X) "F" / ("RT" ln 10)where:"F" is the
Faraday constant;:"R" is the molar gas constant;:"T" is the thermodynamic temperature.
Defined this way, pH is a quantity of dimension 1, that is it has no unit. Values pH(S) for a range of standard solutions S are listed in [http://www.iupac.org/publications/pac/1985/pdf/5703x0531.pdf Definitions of pH scales, standard reference values, measurement of pH, and related terminology] . Pure Appl. Chem. (1985), 57, pp 531–542, where further details can be found.
pH has no fundamental meaning; its official definition is a practical one. However in the restricted range of dilute aqueous solutions having amount-of-substance concentrations less than 0.1 mol/L, and being neither strongly alkaline nor strongly acidic (2 < pH < 12), the definition is such that
:pH = −log10 ["c"(H+) "y"1 / (1 mol/L)] ± 0.02
where "c"(H+) denotes the amount-of-substance concentration of hydrogen ion H+ and "y"1 denotes the activity coefficient of a typical uni-univalent electrolyte in the solution.
Wikimedia Foundation. 2010.