Hypochlorous acid

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Structural formula
Structure of hypochlorous acid
Surname Hypochlorous acid
other names
  • Hypochlorous acid (obsolete)
  • Chloro (I) acid
Molecular formula HClO
Brief description

Slightly yellow colored, chlorine-lime-like smelling substance that is only persistent in aqueous solution.

External identifiers / databases
CAS number 7790-92-3
EC number 232-232-5
ECHA InfoCard 100.029.302
PubChem 24341
Wikidata Q407318
Molar mass 52.46 g mol −1
pK s value



soluble in water

safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hypochlorous acid ( HClO , obsolete hypochlorous acid ) is a colorless (concentrated solutions are colored pale yellow by dichloroxide ), chlorine-lime- like smelling, only weakly dissociating acid . It has a whitening and oxidizing effect .

Extraction and presentation

It is produced by introducing chlorine into water and at the same time removing the hydrochloric acid produced by mercury oxide.

Chloride-free hypochlorous acid can also be produced by reacting dichloroxide with water.


The acid is unstable and can only be produced in an aqueous solution. Even in low concentrations it tends to disproportionate to chloric acid and hydrochloric acid .

The salts and esters of hypochlorous acid are called hypochlorites .

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:

Normal potential at
pH = 0 pH = 14
ClO -  / Cl - +1495 mV +855 mV


Disinfection of bath water in swimming pools, for example with long-term chlorination with trichloroisocyanuric acid tablets (TCCS), which slowly react with the pool water to form cyanuric acid and hypochlorous acid. In rare cases, hypochlorous acid is also used to treat drinking water .

safety instructions

Hypochlorous acid is only a weak acid; However, due to its strong oxidizing effect, it can still cause skin irritation and even chemical burns. When they disintegrate, highly caustic substances such as chloric acid and hydrochloric acid are produced , which can completely kill or even completely decompose organic tissue within a very short time. It should be noted that hypochlorous acid must never be used to oxidize alcohols, as it can esterify them to form highly explosive alkyl hypochlorites . The explosive nitrogen trichloride is formed with ammonia .

Web links

Commons : Hypochlorous Acid  - Collection of pictures, videos and audio files

Individual evidence

  1. a b Entry on hypochlorous acid in the GESTIS substance database of the IFA , accessed on February 27, 2017(JavaScript required) .
  2. ^ A b c d A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , pp. 466-468.
  3. This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  4. G. Brauer (ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Volume 1, Academic Press 1963, pp. 308-309.
  5. ↑ Redox potential and free chlorine. (No longer available online.) Biostel Technology, archived from the original on May 20, 2016 ; accessed on May 20, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.biostel-technology.ch