Editing Ethanol (section)

== Chemistry ==
{{more citations needed section|date=November 2024}}
{{Further|Ethanol (data page)}}

Ethanol is a 2-carbon [[Alcohol (chemistry)|alcohol]]. Its [[molecular formula]] is {{chem2|CH3CH2OH}}. The structure of the molecule of ethanol is {{chem2|CH3\sCH2\sOH}} (an [[ethyl group]] linked to a [[hydroxyl group]]), which indicates that the carbon of a [[methyl group]] ({{chem2|\sCH3}}) is attached to the carbon of a [[methylene group]] ({{chem2|\sCH2\s}}), which is attached to the oxygen of a hydroxyl group ({{chem2|\sOH}}). It is a constitutional [[isomer]] of [[dimethyl ether]]. Ethanol is sometimes abbreviated as '''EtOH''', using the common organic chemistry notation of representing the ethyl group ({{chem2|\sCH2CH3}}) with '''Et'''.

=== Physical properties ===
[[File:Spiritusflamme mit spektrum.png|thumb|upright|Ethanol burning with its spectrum depicted]]

Ethanol is a volatile, colorless liquid that has a slight odor. It burns with a smokeless blue flame that is not always visible in normal light. The physical properties of ethanol stem primarily from the presence of its hydroxyl group and the shortness of its carbon chain. Ethanol's hydroxyl group is able to participate in hydrogen bonding, rendering it more viscous and less volatile than less polar organic compounds of similar molecular weight, such as [[propane]].{{citation needed|date=November 2024}} Ethanol's [[adiabatic flame temperature]] for combustion in air is 2082&nbsp;°C or 3779&nbsp;°F.<ref name="chemss">{{cite news | url=http://www.che.msstate.edu/pdfs/fuel_cell_curriculum/me_mods/ME_Combustion_And_Air_Pollution_Module_1.doc | title=Flame Temperature Analysis and NOx Emissions for Different Fuels | publisher=Mississippi State Department of Chemical Engineering}}</ref>

Ethanol is slightly more refractive than water, having a [[refractive index]] of 1.36242 (at λ=589.3&nbsp;nm and {{convert|18.35|C|F|disp=or}}).<ref name="crc" /> The [[triple point]] for ethanol is {{nowrap|150 ± 20 [[Kelvin|K]]}}.<ref>{{Cite web | date=2023 | title=Ethanol | url=https://webbook.nist.gov/cgi/inchi/InChI%3D1S/C2H6O/c1-2-3/h3H%2C2H2%2C1H3 | access-date=2023-12-23 | website=NIST Chemistry WebBook, SRD 69}}</ref>

=== Solvent properties ===
Ethanol is a versatile solvent, [[miscible]] with water and with many organic solvents, including [[acetic acid]], [[acetone]], [[benzene]], [[carbon tetrachloride]], [[chloroform]], diethyl ether, ethylene glycol, [[glycerol]], [[nitromethane]], [[pyridine]], and [[toluene]]. Its main use as a solvent is in making tincture of iodine, cough syrups, etc.<ref name="crc" /><ref name="merck" /> It is also miscible with light aliphatic hydrocarbons, such as [[pentane]] and [[hexane]], and with aliphatic chlorides such as [[1,1,1-Trichloroethane|trichloroethane]] and [[tetrachloroethylene]].<ref name="merck">{{cite book | last=Windholz | first=Martha | name-list-style=vanc | title=The Merck index: an encyclopedia of chemicals and drugs | publisher=Merck | location=Rahway, NJ | year=1976 | isbn=978-0-911910-26-1 | edition=9th}}{{page needed|date=February 2014}}</ref>

Ethanol's miscibility with water contrasts with the immiscibility of longer-chain alcohols (five or more carbon atoms), whose water miscibility decreases sharply as the number of carbons increases.<ref name="m_and_b">{{cite book | last1=Morrison | first1=Robert Thornton | last2=Boyd | first2=Robert Neilson | name-list-style=vanc | title=Organic Chemistry | url=https://archive.org/details/organicchemistry00morrrich | url-access=registration | edition=2nd | year=1972 | publisher=Allyn and Bacon, inc. | isbn=978-0-205-08452-4}}{{page needed|date=February 2014}}</ref> The miscibility of ethanol with [[alkane]]s is limited to alkanes up to [[undecane]]: mixtures with [[dodecane]] and higher alkanes show a [[miscibility gap]] below a certain temperature (about 13&nbsp;°C for dodecane<ref>{{cite journal | vauthors=Dahlmann U, Schneider GM | title=(Liquid + liquid) phase equilibria and critical curves of (ethanol + dodecane or tetradecane or hexadecane or 2,2,4,4,6,8,8-heptamethylnonane) from 0.1 MPa to 120.0 MPa | journal=J Chem Thermodyn | volume=21 | pages=997–1004 | year=1989 | doi=10.1016/0021-9614(89)90160-2 | issue=9 | bibcode=1989JChTh..21..997D}}</ref>). The miscibility gap tends to get wider with higher alkanes, and the temperature for complete miscibility increases.

Ethanol-water mixtures have less volume than the sum of their individual components at the given fractions. Mixing equal volumes of ethanol and water results in only 1.92 volumes of mixture.<ref name="crc">{{cite book | editor-last=Lide | editor-first=D. R. | name-list-style=vanc | title=CRC Handbook of Chemistry and Physics 81st edition | publisher=CRC press | year=2000 | isbn=978-0-8493-0481-1}}</ref>{{sfn|Lodgsdon|1991|p=813}} Mixing ethanol and water is [[exothermic]], with up to 777&nbsp;J/mol<ref>{{cite journal | vauthors=Costigan MJ, Hodges LJ, Marsh KN, Stokes RH, Tuxford CW | title=The Isothermal Displacement Calorimeter: Design Modifications for Measuring Exothermic Enthalpies of Mixing | journal=Aust. J. Chem. | volume=33 | issue=10 | page=2103 | year=1980 | doi=10.1071/CH9802103 | bibcode=1982AuJCh..35.1971I}}</ref> being released at 298&nbsp;K.

[[File:Ethanol-xtal-1976-3D-balls.png|thumb|Hydrogen bonding in solid ethanol at −186&nbsp;°C]]

Hydrogen bonding causes pure ethanol to be [[hygroscopic]] to the extent that it readily absorbs water from the air. The polar nature of the hydroxyl group causes ethanol to dissolve many ionic compounds, notably [[sodium hydroxide|sodium]] and [[potassium hydroxide]]s, [[magnesium chloride]], [[calcium chloride]], [[ammonium chloride]], [[ammonium bromide]], and [[sodium bromide]].<ref name="merck" /> [[Sodium chloride|Sodium]] and [[potassium chloride]]s are slightly soluble in ethanol.<ref name="merck" /> Because the ethanol molecule also has a nonpolar end, it will also dissolve nonpolar substances, including most [[essential oil]]s<ref name="merckoils">''Merck Index of Chemicals and Drugs'', 9th ed.; monographs 6575 through 6669</ref> and numerous flavoring, coloring, and medicinal agents.

The addition of even a few percent of ethanol to water sharply reduces the [[surface tension]] of water. This property partially explains the "[[tears of wine]]" phenomenon. When wine is swirled in a glass, ethanol evaporates quickly from the thin film of wine on the wall of the glass. As the wine's ethanol content decreases, its surface tension increases and the thin film "beads up" and runs down the glass in channels rather than as a smooth sheet.

=== Azeotrope with water ===
At atmospheric pressure, mixtures of ethanol and water form an [[azeotrope]] at about 89.4&nbsp;[[mol%]] ethanol (95.6% ethanol by mass,<ref name=NIST-SR1828>{{Cite web | last=National Institute of Standards and Technology | title=Standard Reference Material 1828: Ethanol-Water Solutions | url=https://tsapps.nist.gov/srmext/certificates/archives/1828.pdf}}</ref> 97% [[alcohol by volume]]), with a boiling point of 351.3&nbsp;K (78.1&nbsp;°C).<ref name=PembertonMash>{{cite journal | vauthors=Pemberton RC, Mash CJ | title=Thermodynamic properties of aqueous non-electrolyte mixtures II. Vapour pressures and excess Gibbs energies for water + ethanol at 303.15 to 363.15 K determined by an accurate static method | journal=J Chem Thermodyn | volume=10 | pages=867–888 | year=1978 | doi=10.1016/0021-9614(78)90160-X | issue=9 | bibcode=1978JChTh..10..867P}}</ref> At lower pressure, the composition of the ethanol-water azeotrope shifts to more ethanol-rich mixtures.<ref name="Beebe1942">{{cite journal | last1=Beebe | first1=A. H. | last2=Coulter | first2=K. E. | last3=Lindsay | first3=R. A. | last4=Baker | first4=E. M. | title=Equilibria in Ethanol-Water System at Pressures Less Than Atmospheric | journal=Industrial & Engineering Chemistry | date=December 1942 | volume=34 | issue=12 | pages=1501–1504 | doi=10.1021/ie50396a019}}</ref> The minimum-pressure azeotrope has an ethanol fraction of 100%<ref name="Beebe1942"/> and a boiling point of 306&nbsp;K (33&nbsp;°C),<ref name=PembertonMash/> corresponding to a pressure of roughly 70&nbsp;[[torr]] (9.333&nbsp;kPa).<ref name=PressureSwingDistillation>{{Cite web | title=6.4 Pressure swing distillation {{!}} Hyper-TVT: on line Thermische VerfahrensTechnik | work=Institute of Process Engineering {{!}} ETH Zurich | date=10 November 2003 | access-date=12 October 2024 | url=https://www.hyper-tvt.ethz.ch/distillation-azeotrope-pressure_swing.html | language=en}}</ref> Below this pressure, there is no azeotrope, and it is possible to distill absolute ethanol from an ethanol-water mixture.<ref name=PressureSwingDistillation/>

=== Flammability ===
An ethanol–water solution will catch fire if heated above a temperature called its [[flash point]] and an ignition source is then applied to it.<ref name="flash point">{{cite web | url=http://www.nttworldwide.com/tech2212.htm | title=Flash Point and Fire Point | website=Nttworldwide.com | url-status=dead | archive-url=https://web.archive.org/web/20101214222420/http://www.nttworldwide.com/tech2212.htm | archive-date=14 December 2010 | df=dmy}}</ref> For 20% alcohol by mass (about 25% by volume), this will occur at about {{convert|25|°C|°F}}. The flash point of pure ethanol is {{convert|13|°C|°F}},<ref name="NFPA 325">{{cite book | title=NFPA 325: Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids | date=1 January 1994 | publisher=National Fire Protection Association (NFPA) | location=Quincy, Massachusetts | url=https://standards.globalspec.com/std/638448/NFPA%20325}}</ref> but may be influenced very slightly by atmospheric composition such as pressure and humidity. Ethanol mixtures can ignite below average room temperature. Ethanol is considered a flammable liquid (Class 3 Hazardous Material) in concentrations above 2.35% by mass (3.0% by volume; 6 [[Alcohol proof|proof]]).<ref name="49 CFR 173.120">{{cite web | title=49 CFR §&nbsp;173.120 – Class 3 – Definitions. | publisher=Legal Information Institute | url=https://www.law.cornell.edu/cfr/text/49/173.120 | quote=a flammable liquid (Class 3) means a liquid having a flash point of not more than 60 °C (140 °F)}}</ref><ref name="Martínez et al" /><ref name="49 CFR 172.101">{{cite web | title=49 CFR §&nbsp;172.101 – Purpose and use of hazardous materials table. | publisher=Legal Information Institute, Cornell University | url=https://www.law.cornell.edu/cfr/text/49/172.101 | quote=Hazardous materials descriptions and proper shipping names: Ethanol or Ethyl alcohol or Ethanol solutions or Ethyl alcohol solutions; Hazard class or Division: 3; Identification Numbers: UN1170; PG: II; Label Codes: 3;}}</ref> Dishes using burning alcohol for culinary effects are called [[flambé]].
<!-- Mass % and volume % (ABV) are not the same. You must convert weight percent to volume percent to compare the values in the table below to common beer and wine values (which are labeled ABV, or "alcohol by volume"). For example, 5 wt% ethanol in water is approximately 6.3 vol% ethanol in water. -->

{| class="wikitable mw-collapsible mw-collapsed" style="white-space: nowrap; text-align: center;"
|+ Flash points of ethanol–water mixtures<ref name="Ha et al">{{cite journal | last1=Ha | first1=Dong-Myeong | last2=Park | first2=Sang Hun | last3=Lee | first3=Sungjin | title=The Measurement of Flash Point of Water-Methanol and Water-Ethanol Systems Using Seta Flash Closed Cup Tester | journal=Fire Science and Engineering | date=April 2015 | volume=29 | issue=2 | pages=39–43 | doi=10.7731/KIFSE.2015.29.2.039 | url=https://www.researchgate.net/publication/277973979 | quote=Page 4, Table 3}}</ref><ref name="Martínez et al">{{cite journal | last1=Martínez | first1=P. J. | last2=Rus | first2=E. | last3=Compaña | first3=J. M. | title=Flash Point Determination of Binary Mixtures of Alcohols, Ketones and Water | journal=Departamento de Ingeniería Química, Facultad de Ciencias | url=https://engage.aiche.org/HigherLogic/System/DownloadDocumentFile.ashx?DocumentFileKey=e53a8ccc-48b1-4e3b-b59f-bb579cc5132b&ssopc=1 | at=p. 3, Table 4}}</ref><ref name="eng">{{cite web | url=http://www.engineeringtoolbox.com/ethanol-water-d_989.html | title=Flash points of ethanol-based water solutions | access-date=23 June 2011 | website=Engineeringtoolbox.com}}</ref>
! rowspan="2" | Ethanol<br /> [[mole fraction]], %
! colspan="2" | Temperature
|-
! °C
! °F
|-
| 1 || {{convert|84.5|°C|°F|disp=table}}<ref name="Martínez et al" />
|-
| 2 || {{convert|64|°C|°F|disp=table}}<ref name="Martínez et al" />
|-
| 2.35 || {{convert|60|°C|°F|disp=table}}<ref name="Martínez et al" /><ref name="49 CFR 173.120" />
|-
| 3 || {{convert|51.5|°C|°F|disp=table}}<ref name="Martínez et al" />
|-
| 5 || {{convert|43|°C|°F|disp=table}}<ref name="Ha et al" />
|-
| 6 || {{convert|39.5|°C|°F|disp=table}}<ref name="Martínez et al" />
|-
| 10 || {{convert|31|°C|°F|disp=table}}<ref name="Ha et al" />
|-
| 20 || {{convert|25|°C|°F|disp=table}}<ref name="Martínez et al" />
|-
| 30 || {{convert|24|°C|°F|disp=table}}<ref name="Ha et al" />
|-
| 50 || {{convert|20|°C|°F|disp=table}}<ref name="Ha et al" /><ref name="Martínez et al" />
|-
| 70 || {{convert|16|°C|°F|disp=table}}<ref name="Ha et al" />
|-
| 80 || {{convert|15.8|°C|°F|disp=table}}<ref name="Martínez et al" />
|-
| 90 || {{convert|14|°C|°F|disp=table}}<ref name="Ha et al" />
|-
| 100 || {{convert|12.5|°C|°F|disp=table}}<ref name="Ha et al" /><ref name="Martínez et al" /><ref name="NFPA 325" />
|}