Perchloric acid
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2008-07-03T03:58:30Z
Numbo3-bot
7118326
robot Adding: [[tr:Perklorik asit]]
{{Chembox new
| ImageFile = Perchloric-acid-2D-dimensions.png
| IUPACName = Perchloric acid; hydroxidotrioxidochlorine
| Section1 = {{Chembox Identifiers
| SMILES = OCl(=O)(=O)=O
| CASNo = 7601-90-3
| RTECS = SC7500000
}}
| Section2 = {{Chembox Properties
| Formula = [[Hydrogen|H]][[Perchlorate|ClO<sub>4<sub>]]
| MolarMass = 100.46 g/mol
| Appearance = colorless liquid
| Solubility = Miscible
| BoilingPt = 203 °C
}}
| Section7 = {{Chembox Hazards
| EUClass = Oxidant ('''O''')<br/>Corrosive ('''C''')
| NFPA-H = 3 | NFPA-R = 3 | NFPA-O = OX
| RPhrases = {{R5}}, {{R8}}, {{R35}}
| SPhrases = {{S1/2}}, {{S23}}, {{S26}}, {{S36}}, {{S45}}
}}
}}
'''Perchloric acid''', HClO<sub>4</sub>, is an [[oxoacid]] of [[chlorine]] and is a colorless liquid soluble in [[water (molecule)|water]]. It is a [[strong acid]] comparable in strength to [[sulfuric acid]] or [[nitric acid]]. It is a [[superacid]], but it is not the strongest [[Brønsted-Lowry acid-base theory|Brønsted-Lowry acid]] (which is [[fluoroantimonic acid]], HSbF<sub>6</sub>). Its [[pKa|pK<sub>a</sub>]] is −7.<ref>[http://www.chembuddy.com/?left=BATE&right=dissociation_constants dissociation constants]</ref>
Anhydrous perchloric acid is an oily liquid. It forms a series of hydrates, several of which have been characterized [[X-ray crystallography|crystallographically]]. The dihydrate is representative: the solid consists of the [[perchlorate]] anion linked to H<sub>2</sub>O and [[Hydronium|H<sub>3</sub>O<sup>+</sup>]] centers via [[hydrogen bond]]s.<ref>Almlöf, Jan; Lundgren, Jan O.; Olovsson, Ivar "Hydrogen Bond Studies. XLV. Crystal structure of perchloric acid 2.5 hydrate" [[Acta Crystallographica Section B]]: Structural Crystallography and Crystal Chemistry (1971), 27(Pt. 5), 898-904.</ref> Perchloric acid forms an [[azeotrope]] with water, about 72.5% perchloric acid. This form of the acid is stable indefinitely and is commercially available. Such solutions are [[hygroscopy|hygroscopic]], that is, if left unsealed, concentrated acid dilutes itself by absorbing water from the air.
A 0.100 molar solution in [[Acetic acid|glacial acetic acid]] is used as an analytical reagent. [[Titration]] of weak [[Base (chemistry)|bases]] is made easier if the usual medium, water, is replaced by glacial acetic acid. Glacial acetic acid is a much weaker base than water, so the base being titrated appears to be stronger. As a counterpart, the strength of acids is reduced. This shows the difference in strength among the strong acids.
==Laboratory preparation==
The diluted acid can be prepared by [[distillation]] of a solution of sodium [[perchlorate]] in concentrated sulfuric acid.
:NaClO<sub>4</sub> + H<sub>2</sub>SO<sub>4</sub> → NaHSO<sub>4</sub> + HClO<sub>4</sub>
In a related method, [[barium perchlorate]] reacts with dilute sulfuric acid to precipitate [[barium sulfate]], leaving only perchloric acid in solution. It also can be made by mixing [[nitric acid]] with [[ammonium perchlorate]]. The reaction gives [[nitrous oxide]] and perchloric acid due to a concurrent reaction involving the ammonium ion. Its pK<sub>a</sub> is -10.
==Safety==
Anhydrous and monohydrated perchloric acid can explode, and it slowly decomposes at normal temperature. According to the CRC "Handbook of Laboratory Safety", perchloric acid is extremely hazardous. It is very corrosive to skin and eyes and should be handled with the utmost care. It can also ignite or explode upon contact with organic material such as cloth or wood. The salts of perchloric acid are powerful oxidizers that are often used in explosive compositions. Perchlorate salts tend to be less reactive and more stable than their [[chlorate]] counterparts, which has led to their increased use in [[pyrotechnic]] compositions due to safety concerns.
==References==
<references/>
==External links==
*[http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc10/icsc1006.htm International Chemical Safety Card 1006]
[[Category:Perchlorates|*]]
[[Category:Acids]]
[[cs:Kyselina chloristá]]
[[de:Perchlorsäure]]
[[es:Ácido perclórico]]
[[fr:Acide perchlorique]]
[[ko:과염소산]]
[[it:Acido perclorico]]
[[he:חומצה על-כלורית]]
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[[nl:Waterstofperchloraat]]
[[ja:過塩素酸]]
[[pl:Kwas nadchlorowy]]
[[pt:Ácido perclórico]]
[[ro:Acid percloric]]
[[ru:Хлорная кислота]]
[[sr:Перхлорна киселина]]
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[[zh:高氯酸]]