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Acid strength#Strong acids

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+#REDIRECT [[Acid strength#Strong acids]]
-{{Acids and bases}}
-A '''strong acid''' is an [[acid]] that [[Ionization|ionizes]] completely in an [[aqueous solution]] by losing one [[proton]], according to the equation
-:HA(aq) → H<sup>+</sup>(aq) + A<sup>−</sup>(aq)
-For [[sulfuric acid]] which is [[diprotic acid|diprotic]], the "strong acid" designation refers only to dissociation of the first proton
-:H<sub>2</sub>SO<sub>4</sub>(aq) → H<sup>+</sup>(aq) + HSO<sub>4</sub><sup>−</sup>(aq)
-More precisely, the acid must be stronger in aqueous solution than [[hydronium]] ion, so strong acids are acids with a [[acid dissociation constant|p''K''<sub>a</sub>]] < −1.74. An example is [[Hydrochloric acid|HCl]] for which pK<sub>a</sub> = -6.3.<ref name="Jolly"/> This generally means that in aqueous solution at [[standard temperature and pressure]], the concentration of hydronium ions is equal to the concentration of strong acid introduced to the solution.  While strong acids are generally assumed to be the most [[corrosive substance|corrosive]], this is not always true.  The [[carborane]] [[superacid]] H(CHB<sub>11</sub>Cl<sub>11</sub></sub>), which is one million times stronger than [[sulfuric acid]],<ref>George A. Olah, et. al. ''Superacid Chemistry'', 2nd ed., Wiley, p.&nbsp;41.</ref><ref>That is, the ability of the carborane superacid to protonate a given base (B) is one million times greater than a solution of sulfuric acid, so that the ratio [BH<sup>+</sup>] / [B] is one million times higher. The relative acidities of strong acids can be evaluated using the [[Hammett acidity function]].</ref> is entirely non-corrosive, whereas the [[weak acid]] [[hydrofluoric acid]] (HF) is extremely corrosive and can dissolve, among other things, glass and all metals except [[iridium]]{{Citation needed|date=January 2010}}.
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-In all other acid-water reactions, dissociation is not complete, so will be represented as an equilibrium, not a completed reaction.  The typical definition of a [[weak acid]] is any acid that does not dissociate completely.  The difference separating the [[acid dissociation constant]]s of strong acids from all other acids is so small that this is a reasonable demarcation.
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-Due to the complete dissociation of strong acids in aqueous solution, the concentration of hydronium ions in the water is equal to the total concentration (ionized and un-ionized) of the acid introduced to solution: [H<sup>+</sup>] = [A<sup>−</sup>] = [HA]<sub>total</sub> and pH = −log[H<sup>+</sup>].
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-==Determining acid strength==
-The strength of an acid, in comparison to other acids, can be determined without the use of [[pH]] calculations by observing the following characteristics:
-# '''Electronegativity''': The higher the [[electronegativity]] of a [[conjugate base]] in the same period, the more acidic.
-# '''Atomic Radius''': With increasing atomic radius, acidity also increases. For example, HCl and HI, both strong acids, ionize 100% in water to become their respective ionic constituents. However, HI is stronger than HCl. This is because the atomic radius of an atom of iodine is much larger than that of a chlorine atom. As a result, the negative charge over the I<sup>-</sup> anion is dispersed over a larger electron cloud and its attraction for the proton (H<sup>+</sup>) is not as strong as the same attraction in HCl. Therefore, HI is ionized (deprotonated) more readily.
-# '''Charge''': The more positively charged a species is, the more acidic (neutral molecules can be stripped of protons more easily than anions, and cations are more acidic than comparable molecules).
-==Some common strong acids (as defined above)==
-(Strongest to the weakest)
-* [[Hydroiodic acid]] HI ([[acid dissociation constant|pK<sub>a</sub>]] = −9.3)<ref name="Jolly">William L. Jolly "Modern Inorganic Chemistry" (McGraw-Hill, 1984), p.177</ref>
-* [[Hydrobromic acid]] HBr (pK<sub>a</sub> = −8.7)<ref name="Jolly"/>
-* [[Perchloric acid]] HClO<sub>4</sub> (pK<sub>a</sub> ≈ −8)<ref name="Housecroft">{{Housecroft2nd|page=171}}</ref>
-* [[Hydrochloric acid]] HCl (pK<sub>a</sub> = −6.3)<ref name="Jolly"/>
-* [[Sulfuric acid]] H<sub>2</sub>SO<sub>4</sub> (first dissociation only, ''pK''<sub>a1</sub> ≈ −3)<ref name="Housecroft"/>
-* [[p-Toluenesulfonic acid]] (pK<sub>a</sub> = −2.8) Organic soluble strong acid
-== Almost strong acids ==
-These do not meet the strict criterion of being more acidic than H<sub>3</sub>O<sup>+</sup>, although in very dilute solution they dissociate almost completely, so sometimes they are included as "strong acids"
-* [[Hydronium ion]] H<sub>3</sub>O<sup>+</sup> (pK<sub>a</sub> = -1.74). For purposes of simplicity, H<sub>3</sub>O<sup>+</sup> is often replaced in a chemical equation with H<sup>+</sup>. However, a bare proton does not exist free in water but instead is bound to one of the lone pairs of electrons on the H<sub>2</sub>O molecule.
-* [[Nitric acid]] HNO<sub>3</sub> (pK<sub>a</sub> = -1.64)<ref name="Housecroft"/>
-* [[Chloric acid]] HClO<sub>3</sub> (pK<sub>a</sub> = -1.0)<ref name="Housecroft"/>
-* Some chemists include [[bromic acid]] (HBrO<sub>3</sub>){{Citation needed|date=June 2009}},  [[perbromic acid]] (HBrO<sub>4</sub>){{Citation needed|date=June 2009}}, [[iodic acid]] (HIO<sub>3</sub>){{Citation needed|date=June 2009}}, and [[periodic acid]] (HIO<sub>4</sub>){{Citation needed|date=June 2009}} as strong acids, although these are not universally accepted.
-===Extremely strong acids (as protonators)===
-(Strongest to weakest)
-* [[Fluoroantimonic acid]] H[SbF<sub>6</sub>]
-* [[Magic acid]] FSO<sub>3</sub>HSbF<sub>5</sub>
-* [[Carborane superacid]] H(CHB<sub>11</sub>Cl<sub>11</sub>)
-* [[Fluorosulfuric acid]] FSO<sub>3</sub>H
-* [[Triflic acid]] CF<sub>3</sub>SO<sub>3</sub>H
-==References==
-{{reflist}}
-*Hill, John W., et al. "General Chemistry." 4th ed. New Jersey: Prentice Hall, 2005.
-==External links==
-* http://www.cm.utexas.edu/academic/courses/Spring2002/CH301/McDevitt/strong.htm
-* http://jchemed.chem.wisc.edu/Journal/Issues/2000/Jul/abs849.html
-* Titration of acids [http://www2.iq.usp.br/docente/gutz/Curtipot_.html - freeware for data analysis] and simulation of potentiometric [[titration curves]]
-* Acids and Bases [http://www.sky-web.pwp.blueyonder.co.uk/Science/acids.htm - definitions]
-[[Category:Acids]]
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