Hypohalous acid explained

A hypohalous acid is an oxyacid consisting of a hydroxyl group single-bonded to any halogen. Examples include hypofluorous acid, hypochlorous acid, hypobromous acid, and hypoiodous acid. The conjugate base is a hypohalite. They can be formed by reacting the corresponding diatomic halogen molecule with water in the reaction:

This also results in the corresponding hydrogen halide, which is also acidic.

Stability

Hypohalous acids tend to be unstable. Only hypofluorous acid has been isolated as a solid, and even it is explosive at room temperature.[1] Hypochlorous acid cannot be prepared in anhydrous form.[2] Hypobromous acid, hypoiodous acid, and their conjugate bases (hypobromite and hypoiodite) are also unstable, undergoing disproportionation reactions like

and

that result in the corresponding hydrogen halides/halide ions and halic acids/halates.[3]

Uses

Hypochlorous acid and hypobromous acid are each dissolved in water in order to sanitize it, hypochlorous acid in swimming pools and hypobromous acid in hot tubs and spas.[4]

Acidity

Hypohalous acids tend to be weak acids, and they tend to get weaker as the halogen progresses farther down the periodic table. Hypochlorous acid has a pKa of 7.53.[5] The pKa values of hypobromous acid is higher (meaning that it is an even weaker acid),[6] at 8.65. The pKa of hypoiodous acid is even higher, at 10.6.[7]

Notes and References

  1. W. Poll . G. Pawelke . D. Mootz . E. H. Appelman . The Crystal Structure of Hypofluorous Acid : Chain Formation by O−H···O Hydrogen Bonds . . 1988 . 27 . 3 . 392–3 . 10.1002/anie.198803921.
  2. Inorganic chemistry, Egon Wiberg, Nils Wiberg, Arnold Frederick Holleman, "Hypochlorous acid" p.442, section 4.3.1
  3. Book: Holleman . A. F. . Wiberg . Egon . Wiberg . Nils . Inorganic Chemistry . 2001 . Academic Press . 9780123526519 . 451 . 24 September 2018 . en.
  4. Book: Gonick . Larry . Criddle . Craig . The cartoon guide to chemistry . registration . HarperResource . 9780060936778 . 189 . 1st . English . Chapter 9 Acid Basics . Similarly, we add HOCl to swimming pools to kill bacteria.. 2005-05-03 .
  5. Book: Harris, Daniel C.. 2009. Exploring Chemical Analysis . limited. Fourth . 538.
  6. Book: Holleman . A. F. . Wiberg . Egon . Wiberg . Nils . Inorganic Chemistry . 2001 . Academic Press . 9780123526519 . 449 . 7 October 2018 . en.
  7. Web site: Oxoacids Introduction to Chemistry . courses.lumenlearning.com . 26 February 2019 . HOCl pKa = 7.5 < HOBr pKa = 8.6 < HOI pKa = 10.6.