Chemical chameleon
File:Chemical chameleon redox reaction (permanganate).ogg
The chemical chameleon is a redox reaction, well known from classroom demonstrations, that exploits the dramatic color changes associated with the various oxidation states of manganese.{{Cite web |url=http://www.sciencebrothers.org/the-chemical-chameleon/ |title=Science Brothers: The Chemical Chameleon |access-date=2014-03-20 |archive-date=2015-07-06 |archive-url=https://web.archive.org/web/20150706233827/http://www.sciencebrothers.org/the-chemical-chameleon/ |url-status=dead }}[http://chs-science-maths.blogspot.com/2012/02/oxidation-states-and-chemical-chameleon.html Oxidation states and the Chemical Chameleon] Catholic High School, Petaling Jaya Science and Maths Society
Glauber reported the first description of the production of potassium permanganate when he noted that manganese dioxide (as the mineral pyrolusite) could be reacted at high temperatures with alkali to obtain a material that dissolved in water to give a green solution which slowly shifted to a violet-red.Weeks, M. E. and Leicester, H. M.; Discovery of the Elements, Journal of Chemical Education 1968 This process, similar to that still used in the production of potassium permanganate,Reidies, Arno H. (2002) "Manganese Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a16_123}} oxidized manganese dioxide to potassium manganate which, acidified by carbon dioxide absorbed from the air, oxidized further to purple potassium permanganate.
The chemical chameleon reaction shows the process in reverse, by reducing violet potassium permanganate first to green potassium manganate and eventually to brown manganese dioxide:{{cite web|title=The Chemical Chameleon|url=http://oise-is-chemistry-2011-2012.wikispaces.com/file/view/Chem%20Chameleon%20Handout.docx/317092198/Chem%20Chameleon%20Handout.docx|publisher=Ontario Institute for Studies in Education|accessdate=20 March 2014|format=docx|archive-date=20 March 2014|archive-url=https://web.archive.org/web/20140320202405/http://oise-is-chemistry-2011-2012.wikispaces.com/file/view/Chem%20Chameleon%20Handout.docx/317092198/Chem%20Chameleon%20Handout.docx|url-status=dead}}
:KMnO4 (violet) → K2MnO4 (green) → MnO2 (brown/yellow suspension)
Blue potassium hypomanganate may also form as an intermediate.{{Cite web |url=http://science.perthuniversity.org/chemistry-experiment-kmno4-naoh-sugar/ |title=Faculty of Science Perth University: Chemistry experiment – KMnO4 + NaOH + sugar |access-date=2014-03-20 |archive-url=https://web.archive.org/web/20150316205009/http://science.perthuniversity.org/chemistry-experiment-kmno4-naoh-sugar/ |archive-date=2015-03-16 |url-status=dead }}
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| colspan=2|Oxidation states of manganese{{cite book|title = Anorganische Chemie II.|chapter = VII. Nebengruppe|pages = 100–109|first = Max|last = Schmidt|publisher = Wissenschaftsverlag|year = 1968|language = German}} | |
|---|---|
| +7 | Potassium permanganate (violet) |
| +6 | Potassium manganate (green) |
| +5 | Potassium hypomanganate (blue) |
| +4 | Manganese dioxide (yellow) |
The reaction proceeds in alkaline conditions under the influence of a reducing agent. Sodium hydroxide, potassium hydroxide, and ammonium hydroxide can be used to alkalize the permanganate solution, while a variety of reducing agents can be used, sugars being common.{{cite book|title=Chem C3000 Experiment Manual|publisher=Thames & Kosmos|page=53|url=http://www.thamesandkosmos.com/news/manualsamples/640132_chemc3000v2_manual_sample.pdf|access-date=2014-03-20|archive-url=https://web.archive.org/web/20130407023415/http://thamesandkosmos.com/news/manualsamples/640132_chemc3000v2_manual_sample.pdf|archive-date=2013-04-07|url-status=dead}}
A similar demonstration involves soaking paper in alkalized permanganate solution, which produces the same color changes as the paper is oxidized and the permanganate reduced.{{cite book|last=Thompson|first=Robert Bruce|title=Illustrated Guide to Home Chemistry Experiments|url=https://books.google.com/books?id=iZVCN05SURsC|chapter=Lab 10.2: Oxidation States of Manganese|date=17 February 2012 |isbn=9781449331429 }}