Chloric acid

Structural formula
General
Surname	Chloric acid
other names	Chlorine (V) acid
Molecular formula	HClO 3
Brief description	colorless and odorless acid that only exists as an aqueous solution
External identifiers / databases
CAS number 7790-93-4 EC number 232-233-0 ECHA InfoCard 100.029.303 PubChem 19654 ChemSpider 18513 DrugBank DB14150 Wikidata Q138809
properties
Molar mass	84.46 g mol −1
Physical state	only exists in aqueous solution up to a maximum of 40%
density	1.28 g cm −3 (40% solution)
Melting point	20 ° C (18% solution)
boiling point	40 ° C (decomposition of the 18% solution)
pK s value	−2.7
solubility	very good in water
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 271-314 P: 220-280-305 + 351 + 338-310
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Chloric acid is one of the oxygen acids of chlorine , to also include perchloric acid , hypochlorous acid and chlorous acid . As a pure substance, chloric acid is not stable and only exists in diluted form. The colorless solution is used as a strong oxidizing agent . Some of the salts of chloric acid, the chlorates , are of great industrial importance.

properties

Physical Properties

According to the VSEPR model, chloric acid has a trigonal pyramidal structure.

Chemical properties

Chloric acid is a strong acid (pK _S = ca. -2.7) completely in water in ion dissociated present. Conversely, the chlorate ions have only a slight tendency to accumulate protons, so that they dissolve in water with an approximately neutral pH value.

The chlorine atom in chloric acid has the + V oxidation state. As a typical non-metal, it has a strong tendency to take up electrons in chemical reactions and to convert to a lower, stable oxidation number (−I, 0, + I or + III). Thus, chloric acid is a strong oxidizing agent with a high redox potential . However, chloric acid can also be oxidized to perchloric acid (oxidation number: + VII). In general, the chloric acid is in equilibrium with other oxygen acids of the chlorine, as well as chlorine dioxide and chlorine, via disproptionation and comproportionation reactions . The oxidizing effect is more pronounced in acidic than in alkaline, which is expressed in a higher redox potential. The following results for the individual numerical values:

Redox couple	Oxidation state	Normal potential at pH = 0	Normal potential at pH = 14
HClO 4 / HClO 3	(+ VII) / (+ V)	+1.19 V	+0.36 V
HClO 3 / ClO 2	(+ V) / (+ IV)	+1.18V	?
HClO 3 / HClO 2	(+ V) / (+ III)	?	?
HClO 3 / HClO	(+ V) / (+ I)	+1.43 V	+0.50 V
HClO 3 / Cl 2	(+ V) / (0)	+1.47 V	+0.48 V.
HClO 3 / Cl -	(+ V) / (- I)	+1.45 V	+0.62 V

Extraction and presentation

The representation of chloric acid is based on chlorine, which is first converted into chlorate. The chlorate ions are then protonated to form chloric acid . Chlorine is first introduced into hot sodium hydroxide solution . It disproportionates in an equilibrium reaction into chloride ions and hypochlorite ions (1). The solution is then partially acidified so that some of the hypochlorite ions are converted into hypochlorous acid (2). As a strong oxidizing agent, hypochlorous acid can oxidize hypochlorites to chlorates (3). Since the protons are regenerated in the 3rd step, only very few protons have to be used for acidification in the 2nd step. The reaction equations for the individual steps are:

(1) ${\displaystyle \mathrm {3\ Cl_{2}+6Na^{+}+6OH^{-}\rightleftharpoons \ 3\ Cl^{-}+3\ ClO^{-}+6\ Na^{+}+3\ H_{2}O} }$

(2) ${\displaystyle \mathrm {3\ ClO^{-}+2H^{+}\rightleftharpoons \ 2\ HClO+ClO^{-}} }$

(3) ${\displaystyle \mathrm {2\ HClO+ClO^{-}\rightleftharpoons \ ClO_{3}^{-}+2\ Cl^{-}+2\ H^{+}} }$

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Gross:

${\displaystyle \mathrm {3\ Cl_{2}+6\ OH^{-}\rightleftharpoons \ 5\ Cl^{-}+ClO_{3}^{-}+3\ H_{2}O} }$

Technically, sodium chlorate is produced by electrolysis of an aqueous common salt solution . This creates gaseous hydrogen , chlorine and caustic soda. If the chlorine gas is fed back into the solution or if it is not allowed to escape in gaseous form at all, it can react to form a sodium chlorate solution, as shown above.

Chloric acid is produced by acidifying solutions that contain chlorate ions. If you start from a barium chlorate solution and add dilute sulfuric acid to it, the sparingly soluble barium sulfate precipitates . Only the chloric acid remains in solution.

${\displaystyle \mathrm {Ba(ClO_{3})_{2}(aq)+H_{2}SO_{4}(l)\rightleftharpoons \ 2\ HClO_{3}(aq)+BaSO_{4}(s)} }$

Chloric acid can be concentrated up to a concentration of 40% by means of dehydrating agents. More concentrated solutions decompose with the formation of chlorine , chlorine dioxide and perchloric acid :

${\displaystyle \mathrm {8\ HClO_{3}\longrightarrow \ 4\ HClO_{4}+2\ Cl_{2}+3\ O_{2}+2\ H_{2}O} }$

${\displaystyle \mathrm {3\ HClO_{3}\longrightarrow \ HClO_{4}+2\ ClO_{2}+H_{2}O} }$

use

A commercial mixture of 40% chloric acid with fuming (38%) hydrochloric acid is called Euchlorin (not to be confused with the mineral of the same name ). The combination of strong acidic and oxidizing properties can be used to break down otherwise insoluble minerals and destroy organic substances. The oxidizing effect is not only caused by the chloric acid itself, but also by the chlorine and chlorine dioxide that are formed when reacting with HCl:

${\displaystyle \mathrm {2\ HClO_{3}+2\ HCl\longrightarrow \ 2\ ClO_{2}+Cl_{2}+2\ H_{2}O} }$

safety instructions

Even diluted chloric acid has a fire-promoting character and must not be brought into contact with organic materials.

Individual evidence

1. ↑ ^{a b} Entry on chloric acid. In: Römpp Online . Georg Thieme Verlag, accessed on July 15, 2014.
2. ↑ ^{a b c d e f} Entry on chloric acid in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
3. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .
4. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 , p. 227.
5. ↑ G. Brauer (Ed.): Handbook of Preparative Inorganic Chemistry 2nd Edition, Vol. 1, Academic Press 1963, pp. 312-313.