Definition - What does Hypochlorite mean?

A hypochlorite is a chemical compound containing the molecular ion of chlorine and oxygen (hypochlorite ion OCl-) and a counter-ion such as sodium or calcium. A hypochlorite is also referred to as an ester or salt of hypochlorous acid.

The two most common hypochlorites are calcium hypochlorite (Ca(OCl)2) and sodium hypochlorite (NaOCl). Even though hypochlorites are alkaline, they are the strongest oxidizing agents of all compounds containing chlorine oxyanions.

Corrosionpedia explains Hypochlorite

Common hypochlorites include:

  • Sodium hypochlorite
  • Calcium hypochlorite
  • Barium hypochlorite
  • Lithium hypochlorite
  • Methyl hypochlorite

Hypochlorites are generally unstable and some, like sodium hypochlorite, only exist in solution. Calcium hypochlorite is more stable and available as a white powder, flat plates or pellets. Hypochlorites have a chlorine odor, and become more unstable at higher temperatures.

Applications include:

  • Bleaching
  • Disinfection and water treatment
  • Chlorination and oxidation
  • Sanitization

The hypochlorite ion is aggressive to stainless steel and causes pitting or crevice corrosion at ambient temperatures or stress corrosion cracking at higher temperatures. Corrosion arising from the disinfecting or sanitizing of stainless steel items can be minimized by using dilute hypochlorite solutions at a low temperature, reducing contact time and thorough rinsing.

Typical methods used to prepare hypochlorites are:

  • Disproportionation reaction between a metal hydroxide and chlorine gas performed at room temperature, for industrial production of calcium hypochlorite and sodium hypochlorite
  • Electrochemical reaction via an unseparated chloralkali process, involving electrolyzing brine to form Cl2, which dissolves in water to form the hypochlorite, used for large amounts of sodium hypochlorite
  • Biosynthesis, occurring in the human body where the immune system generates very small amounts of hypochlorite during the destruction of pathogens
  • Salt metathesis reaction, used to prepare small amounts of hypochlorites. The reaction is performed between calcium hypochlorite and various metal sulfates.
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