unit:PH
http://qudt.org/vocab/unit/PH
unit:PHqudt:Unit| Predicate | Object |
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rdf:type |
qudt:Unit |
dcterms:description |
In chemistry the unit \(\textit{pH}\), also referred to as \(\textit{acidity}\) or \(\textit{basicity}\), is the negative logarithm (base 10) of the concentration of free protons (or hydronium ions). The definition of \(pH\) in terms of hydrogen ions in solution is: \[\text{pH}=-\log_{10}(a_{H^+})\equiv-\log_{10}\left(\left[H^+\right]\right)\] Where \(a_{H^+}\) is the equilibrium molar concentration of \(H^+\) in the solution, the activity of the hydrogen ion in the solution. \[\] This definition is appropriate for concentrations equal to, or less than \(1\ mol/l\), where \(aH+ \equiv [H+]\), that is, \(1\ mol/L\ HCl\) has a \(pH\) of zero. \[\] To relate this to standard molality (\(b^\circ\)), typically taken as \(1 \ mol/kg\), consideration is given to the activity (\(a_{H^+}\)) of the hydrogen ions. \[\] The activity can be expressed as: \[a_{H^+} = \gamma_{H^+} \times m_{H^+}\] Where, \(\gamma_{H^+}\) is the activity coefficient, which adjusts the molality to account for non-ideal behavior due to interactions between ions in the solution. \(m_{H^+}\) is the molality of hydrogen ions in the solution relative to the standard molality, expressed in \(mol/kg\). \[\] The expansion of \(pH\) then becomes: \[\text{pH} = -log_{10}\left(m_{H+}\times\gamma_{H^+}\right)\] \[\] This definition is relevant in more concentrated solutions or when precise thermodynamic calculations are required. It reflects how the properties of the solution deviate from ideal behavior and provides a more accurate understanding of the \(pH\) under various conditions. \[\] While \(pH\) is a universally recognized scale for expressing hydrogen ion activity, its appropriateness and accuracy can diminish under conditions of extremely high ionic strength, non-aqueous environments, high temperatures, or very high or low \(pH\) values. In such cases, alternative measurement strategies might be required to obtain meaningful and accurate descriptions of acidity or basicity. |
qudt:applicableSystem |
Show 8 values |
qudt:conversionMultiplier |
0.0 |
qudt:conversionMultiplierSN |
0.0E0 |
qudt:hasDimensionVector |
qkdv:A0E0L0I0M0H0T0D1 |
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qudt:informativeReference |
https://iupac.org/wp-content/uploads/2019/05/IUPAC-GB3-2012-2ndPrinting-PDFsearchable.pdf |
qudt:symbol |
“pH” |
qudt:ucumCode |
“[pH]”^^qudt:UCUMcs |
rdfs:comment |
“Unsure about dimensionality of pH; conversion requires a log function not just a multiplier”@en |
rdfs:isDefinedBy |
http://qudt.org/3.1.11/vocab/unit |
rdfs:label |
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