en>David Eppstein: source

2013-12-14T01:43:50Z

source

← Older revision		Revision as of 03:43, 14 December 2013
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	~~The~~ name of the ~~author~~ is ~~Luther~~. ~~What he really enjoys doing~~ is ~~to perform handball but he~~ is ~~having difficulties to discover time for it~~. ~~She~~ functions as a ~~financial officer~~ and ~~she will not alter it anytime quickly~~. ~~Her husband~~ and ~~her chose~~ to ~~reside in Alabama~~.<br><br>~~my web page~~ ... [~~http:~~//~~www~~.~~Ebc-clan~~.ch/~~index~~.~~php?mod~~=~~users&action~~=~~view&id~~=~~12304 ebc-clan.ch~~]		{{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.]" ''[[Compendium of Chemical Terminology]]''.</ref><ref name="Rochester">Rochester, C. H. (1970). ''Acidity Functions.'' New York: Academic Press.</ref> usually expressed in terms of its ability to donate protons to (or accept protons from) a [[solution\|solute]] ([[Brønsted acid]]ity). The [[pH]] scale is by far the most commonly used acidity function, and is ideal for dilute aqueous solutions. Other acidity functions have been proposed for different environments, most notably the [[Hammett acidity function]], ''H''<sub>0</sub>,<ref name="Hammett">[[Hammett, L. P.]] (1940). ''Physical Organic Chemistry.'' New York: McGraw-Hill.</ref> for [[superacid]] media and its modified version ''H''<sub>−</sub> 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<sup>+</sup>:
			::<math>H_0 = {\rm p}K_{\rm a} + \log {{c_{\rm B}}\over{c_{\rm BH^+}}}</math>
			where p''K''<sub>a</sub> is the [[Acid dissociation constant\|dissociation constant]] of BH<sup>+</sup>. 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="Hammett"/> Other spectroscopic methods, such as [[Nuclear magnetic resonance spectroscopy\|NMR]], may also be used.<ref name="Rochester"/><ref>Cox, R. A.; Yates, K. (1983). [[Canadian Journal of Chemistry\|''Can. J. Chem.'']] '''61''':2245.</ref> The function ''H''<sub>−</sub> 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<sup>−</sup> 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]] H<sub>3</sub>O<sup>+</sup> (or more accurately [H(OH<sub>2</sub>)<sub>n</sub>]<sup>+</sup>). In this case ''H''<sub>0</sub> and ''H''<sub>−</sub> are equivalent to pH values determined by the buffer equation or [[Henderson-Hasselbalch equation]].<br>
			However, an ''H''<sub>0</sub> value of −21 (a 25% solution of [[Antimony pentafluoride\|SbF<sub>5</sub>]] in [[Fluorosulfonic acid\|HSO<sub>3</sub>F]])<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 10<sup>21</sup> mol/dm<sup>3</sup>: such a "solution" would have a density more than a hundred times greater than a [[neutron star]]. Rather, ''H''<sub>0</sub> = −21 implies that the reactivity (protonating power) of the solvated hydrogen ions is 10<sup>21</sup> 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<sup>+</sup>, i.e. [[Brønsted acid]]s. <br>The hydrogen ion H<sup>+</sup> ''never'' exists on its own in a condensed phase, it is always [[Solvation\|solvated]] to a certain extent. The high negative value of ''H''<sub>0</sub> in SbF<sub>5</sub>/HSO<sub>3</sub>F 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 SbF<sub>5</sub>·FSO<sub>3</sub>H is a much stronger proton donor than H<sub>3</sub>O<sup>+</sup>.

			==References==
			<references />

			[[Category:Acids]]
			[[Category:Chemical properties]]
			[[Category:Solvents]]

en>David Eppstein: unreferenced

2012-08-25T15:02:09Z

unreferenced

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The name of the author is Luther. What he really enjoys doing is to perform handball but he is having difficulties to discover time for it. She functions as a financial officer and she will not alter it anytime quickly. Her husband and her chose to reside in Alabama.<br><br>my web page ... [http://www.Ebc-clan.ch/index.php?mod=users&action=view&id=12304 ebc-clan.ch]

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en>David Eppstein: source

en>David Eppstein: unreferenced