Editing Soap (section)

== Types ==
[[File:Decorative Soaps.jpg|thumb|right|A collection of decorative bar soaps, as often found in [[hotel]]s]]

===Toilet soaps===
[[File:Micelle.svg|thumb|upright=1|Structure of a [[micelle]], a cell-like structure formed by the aggregation of soap subunits (such as [[sodium stearate]]): The exterior of the micelle is hydrophilic (attracted to water) and the interior is lipophilic (attracted to oils).]]
In a domestic setting, "soap" usually refers to what is technically called a toilet soap, used for household and personal cleaning. Toilet soaps are salts of fatty acids with the general formula ([[Carboxylate ion|RCO<sub>2</sub><sup>−</sup>]])M<sup>+</sup>, where M is [[Sodium|Na]] (sodium) or [[Potassium|K]] (potassium).<ref name=UllSoap/>

When used for cleaning, soap [[solubilize]]s particles and grime, which can then be separated from the article being cleaned. The insoluble oil/fat "dirt" become associated inside [[micelle]]s, tiny spheres formed from soap molecules with polar [[hydrophile|hydrophilic]] (water-attracting) groups on the outside and encasing a [[lipophilicity|lipophilic]] (fat-attracting) pocket, which shields the oil/fat molecules from the water, making them soluble. Anything that is soluble will be washed away with the water. In [[hand washing]], as a surfactant, when lathered with a little water, soap kills [[microorganism]]s by disorganizing their membrane [[lipid bilayer]] and [[Denaturation (biochemistry)|denaturing]] their [[protein]]s.{{Citation needed|date=September 2023}} It also [[emulsifies]] oils, enabling them to be carried away by running water.<ref>{{Cite web|url=http://cool.conservation-us.org/waac/wn/wn23/wn23-3/wn23-304.html|title=A Brief History of Aluminum Stearate as a Component of Paint|last=Tumosa|first=Charles S.|date=2001-09-01|website=cool.conservation-us.org|language=en|access-date=2017-04-05|url-status=live|archive-url=https://web.archive.org/web/20170318085239/http://cool.conservation-us.org/waac/wn/wn23/wn23-3/wn23-304.html|archive-date=2017-03-18}}</ref>

When used in [[hard water]], soap does not lather well but forms [[soap scum]] (related to [[metallic soap]]s, see below).<ref>{{cite book |last1=Holman |first1=John S. |last2=Stone |first2=Phil |title=Chemistry |url=https://books.google.com/books?id=j9auT6Jd_JMC&pg=PA174 |publisher=Nelson Thornes |date=2001 |page=174 |isbn=9780748762392}}</ref>

===Non-toilet soaps===
So-called [[metallic soap]]s are key components of most lubricating [[grease (lubricant)|greases]] and thickeners.<ref name=UllSoap>{{cite encyclopedia |author=Klaus Schumann |author2=Kurt Siekmann |chapter=Soaps |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |year=2005 |publisher=Wiley-VCH |location=Weinheim |doi=10.1002/14356007.a24_247 |isbn=978-3527306732}}</ref> A commercially important example is [[lithium stearate]]. Greases are usually [[emulsion]]s of [[calcium stearate|calcium soap]] or [[lithium soap]] and [[mineral oil]]. Many other metallic soaps are also useful, including those of [[aluminium]], [[sodium]], and mixtures thereof. Such soaps are also used as thickeners to increase the [[viscosity]] of oils. In ancient times, lubricating greases were made by the addition of [[Lime (material)|lime]] to [[olive oil]], which would produce calcium soaps.<ref>{{cite encyclopedia |author=Thorsten Bartels |display-authors=etal |chapter=Lubricants and Lubrication |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |year=2005 |publisher=Wiley-VCH |location=Weinheim |doi=10.1002/14356007.a15_423 |isbn=978-3527306732}}</ref> Metal soaps are also included in modern artists' [[oil paint]]s formulations as a [[rheology]] modifier.<ref>{{cite web|url=http://cool.conservation-us.org/waac/wn/wn23/wn23-3/wn23-304.html|title=A Brief History of Aluminum Stearate as a Component of Paint|last=S.|first=Tumosa, Charles|date=2001-09-01|website=cool.conservation-us.org|language=en|access-date=2017-03-17|url-status=live|archive-url=https://web.archive.org/web/20170318085239/http://cool.conservation-us.org/waac/wn/wn23/wn23-3/wn23-304.html|archive-date=2017-03-18}}</ref> Metal soaps can be prepared by neutralizing fatty acids with metal oxides:
:2 RCO<sub>2</sub>H + CaO → (RCO<sub>2</sub>)<sub>2</sub>Ca + H<sub>2</sub>O

A cation from an [[organic base]] such as [[ammonium]] can be used instead of a metal; ammonium [[nonanoic acid|nonanoate]] is an ammonium-based soap that is used as an herbicide.<ref name="ammonium">{{cite web |url=https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_PC-031802_01-Nov-06.pdf |title=Ammonium nonanoate (031802) Fact Sheet |website=epa.gov |date=2006-09-21 |access-date=2022-08-15 |archive-date=2022-11-16 |archive-url=https://web.archive.org/web/20221116165514/https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_PC-031802_01-Nov-06.pdf |url-status=live }}</ref>

Another class of non-toilet soaps are [[resin soap]]s, which are produced in the [[paper industry]] by the action of tree rosin with alkaline reagents used to separate cellulose from raw wood. A major component of such soaps is the sodium salt of [[abietic acid]]. Resin soaps are used as emulsifiers.<ref>{{cite book |doi=10.1002/14356007.a23_073 |chapter=Resins, Natural |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |last1=Fiebach |first1=Klemens |last2=Grimm |first2=Dieter |isbn=3-527-30673-0 }}</ref>