EducationBot: Новая страница: «{{Английская Википедия/Панель перехода}} {{short description|Measure of acidity}} {{Acids and bases}} An '''acidity function''' is a measure of the acidity of a medium or solvent system,IUPAC Commission on Physical Organic Chemistry (1994). "[http://www.iupac.org/publications/pac/1994/pdf/6605x1077.pdf Glossary of Terms used in Physical Organic Chemistry.]" ''Pure Appl. Chem.'' '''6...»

2023-12-28T17:17:40Z

Новая страница: «{{Английская Википедия/Панель перехода}} {{short description|Measure of acidity}} {{Acids and bases}} An '''acidity function''' is a measure of the acidity of a medium or solvent system,<ref>IUPAC Commission on Physical Organic Chemistry (1994). "[http://www.iupac.org/publications/pac/1994/pdf/6605x1077.pdf Glossary of Terms used in Physical Organic Chemistry.]" ''Pure Appl. Chem.'' '''6...»

Новая страница

{{Английская Википедия/Панель перехода}}
{{short description|Measure of acidity}}
{{Acids and bases}}
An '''acidity function''' is a measure of the [[acidity]] of a medium or solvent system,<ref>[[IUPAC]] Commission on Physical Organic Chemistry (1994). "[http://www.iupac.org/publications/pac/1994/pdf/6605x1077.pdf Glossary of Terms used in Physical Organic Chemistry.]" [[Pure and Applied Chemistry|''Pure Appl. Chem.'']] '''66''':1077–1184. "[http://goldbook.iupac.org/A00081.html Acidity function.] {{Webarchive|url=https://web.archive.org/web/20130804002131/http://goldbook.iupac.org/A00081.html |date=2013-08-04 }}" ''[[Compendium of Chemical Terminology]]''.</ref><ref name=":0">{{Cite book|last=Rochester|first=Colin H.|url=https://www.worldcat.org/oclc/93620|title=Acidity functions|date=1970|publisher=Academic Press|isbn=0-12-590850-4|location=London|oclc=93620}}</ref> usually expressed in terms of its ability to donate protons to (or accept protons from) a [[solute]] ([[Brønsted acid]]ity). The [[pH]] scale is by far the most commonly used acidity function, and is ideal for dilute [[aqueous solution]]s. Other acidity functions have been proposed for different environments, most notably the [[Hammett acidity function]], ''H''0,<ref name=":1">{{Cite book|last=Hammett|first=Louis Plack|url=https://books.google.com/books?id=Ns_QAAAAMAAJ|title=Physical Organic Chemistry: Reaction Rates, Equilibria, and Mechanisms|date=1940|publisher=McGraw-Hill Book Company, Incorporated|language=en}}</ref> for [[superacid]] media and its modified version ''H''− for [[superbase|superbasic]] media. The term acidity function is also used for measurements made on basic systems, and the term '''basicity function''' is uncommon.

Hammett-type acidity functions are defined in terms of a [[Buffer solution|buffered medium]] containing a weak base B and its [[conjugate acid]] BH+:
::<math>H_0 = {\rm p}K_{\rm a} + \log {{c_{\rm B}}\over{c_{\rm BH^+}}}</math>
where p''K''a is the [[Acid dissociation constant|dissociation constant]] of BH+. They were originally measured by using [[nitroaniline (disambiguation)|nitroaniline]]s as weak bases or [[acid-base indicator]]s and by measuring the concentrations of the protonated and unprotonated forms with [[UV-visible spectroscopy]].<ref name=":1" /> Other spectroscopic methods, such as [[Nuclear magnetic resonance spectroscopy|NMR]], may also be used.<ref name=":0" /><ref>{{Cite journal|last1=Cox|first1=Robin A.|last2=Yates|first2=Keith|date=2011-02-05|title=Acidity functions: an update|url=https://cdnsciencepub.com/doi/abs/10.1139/v83-388|journal=Canadian Journal of Chemistry|volume=61 |issue=10 |pages=2225–2243 |language=en|doi=10.1139/v83-388}}</ref> The function ''H''− is defined similarly for strong bases:
::<math>H_- = {\rm p}K_{\rm a} + \log {{c_{\rm B^-}}\over{c_{\rm BH}}}</math>
Here BH is a weak acid used as an acid-base indicator, and B− is its conjugate base.

==Comparison of acidity functions with aqueous acidity==
In dilute aqueous solution, the predominant acid species is the [[hydronium ion|hydrated hydrogen ion]] H3O+ (or more accurately [H(OH2)n]+). In this case ''H''0 and ''H''− are equivalent to pH values determined by the buffer equation or [[Henderson-Hasselbalch equation]]. 
However, an ''H''0 value of −21 (a 25% solution of [[Antimony pentafluoride|SbF5]] in [[Fluorosulfonic acid|HSO3F]])<ref>Jolly, William L. (1991). ''Modern Inorganic Chemistry'' (2nd Edn.). New York: McGraw-Hill. {{ISBN|0-07-112651-1}}. p. 234.</ref> does not imply a hydrogen ion concentration of 1021 mol/dm3: such a "solution" would have a density more than a hundred times greater than a [[neutron star]]. Rather, ''H''0 = −21 implies that the reactivity ([[protonating]] power) of the solvated hydrogen ions is 1021 times greater than the reactivity of the hydrated hydrogen ions in an aqueous solution of pH 0. The actual reactive species are different in the two cases, but both can be considered to be sources of H+, i.e. [[Brønsted acid]]s. The hydrogen ion H+ ''never'' exists on its own in a condensed phase, as it is always [[Solvation|solvated]] to a certain extent. The high negative value of ''H''0 in SbF5/HSO3F mixtures indicates that the solvation of the hydrogen ion is much weaker in this solvent system than in water. Other way of expressing the same phenomenon is to say that SbF5·FSO3H is a much stronger proton donor than H3O+.

==References==
<references />

[[Category:Acids]]
[[Category:Chemical properties]]
[[Category:Solvents]]
{{Навигационная таблица/Портал/Английская Википедия}}
[[Категория:Английская Википедия]]
[[Категория:Википедия]]
[[Категория:Статья из Википедии]]
[[Категория:Статья из Английской Википедии]]

Английская Википедия:Acidity function - История изменений