Editing Chlorine (section)

==Occurrence==
[[File:Liquid chlorine in flask.jpg|upright|thumb|Liquid chlorine analysis]]
Chlorine is too reactive to occur as the free element in nature but is very abundant in the form of its chloride salts. It is the 20th most abundant element<ref>{{Cite book |last=Experts |first=Arihant |url=https://books.google.com/books?id=bDAnEAAAQBAJ&dq=%2220th+most+abundant+element%22&pg=RA1-PA86 |title=General Nursing and Midwifery Entrance Examination 2021 |date=2020-11-01 |publisher=Arihant Publications India limited |isbn=978-93-252-9132-4 |language=en}}</ref> in Earth's crust and makes up 126&nbsp;[[parts per million]] of it, through the large deposits of chloride minerals, especially [[sodium chloride]], that have been evaporated from water bodies. All of these pale in comparison to the reserves of chloride ions in seawater: smaller amounts at higher concentrations occur in some inland seas and underground [[brine]] wells, such as the [[Great Salt Lake]] in Utah and the [[Dead Sea]] in Israel.<ref name="Greenwood795">{{harvnb|Greenwood|Earnshaw|1997|p=795}}</ref>

Small batches of chlorine gas are prepared in the laboratory by combining hydrochloric acid and [[manganese dioxide]], but the need rarely arises due to its ready availability. In industry, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. This method, the [[chloralkali process]] industrialized in 1892, now provides most industrial chlorine gas.<ref name="Greenwood798" /> Along with chlorine, the method yields [[hydrogen]] gas and [[sodium hydroxide]], which is the most valuable product. The process proceeds according to the following [[chemical equation]]:<ref>{{Holleman&Wiberg|page=408}}</ref>

:2 NaCl + 2 H<sub>2</sub>O → Cl<sub>2</sub> + H<sub>2</sub> + 2 NaOH