Wikipedia:WikiProject Chemicals/Chembox validation/VerifiedDataSandbox and Sodium hydroxide: Difference between pages

{{short description|Chemical compound with formula NaOH}}

{{About|the chemical compound|the commercial product|Lye}}

| Watchedfields = changed

| verifiedrevid = 477162765

| ImageFile1 = SodiumHydroxide.jpg

| ImageName1 = Sample of sodium hydroxide as pellets in a watchglass

| ImageFile = Sodium-hydroxide-crystal-3D-vdW.png

| ImageFile_Ref = {{Chemboximage|correct|??}}

| ImageName = Unit cell, spacefill model of sodium hydroxide

| ImageCaption = {{legend|rgb(128, 64, 224)|[[Sodium]], Na}}{{legend|red|[[Oxygen]], O}}{{legend|white|[[Hydrogen]], H}}

| OtherNames = {{ubl|Ascarite|Caustic soda|[[Lye]]<ref name="msd" /><ref name="msd2" />|Soda lye|Sodium hydrate|White caustic<ref name="PubChem" />}}

| IUPACName = Sodium hydroxide<ref name="PubChem">{{cite web | url=https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=14798&loc=ec_rcs | title=Sodium Hydroxide – Compound Summary | access-date=June 12, 2012}}</ref>

| Section1 = {{Chembox Identifiers

|CASNo = 1310-73-2

|CASNo_Ref = {{cascite|correct|CAS}}

|PubChem = 14798

|ChemSpiderID = 14114

|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

|UNII = 55X04QC32I

|UNII_Ref = {{fdacite|correct|FDA}}

|EINECS = 215-185-5

|UNNumber = 1823 (solid)<br>1824 (solution)

|KEGG = D01169

|KEGG_Ref = {{keggcite|correct|kegg}}

|MeSHName = Sodium+Hydroxide

|ChEBI = 32145

|ChEBI_Ref = {{ebicite|correct|EBI}}

|RTECS = WB4900000

|Gmelin = 68430

|SMILES = [OH-].[Na+]

|StdInChI = 1S/Na.H2O/h;1H2/q+1;/p-1

|StdInChI_Ref = {{stdinchicite|correct|chemspider}}

|InChI = 1/Na.H2O/h;1H2/q+1;/p-1

|StdInChIKey = HEMHJVSKTPXQMS-UHFFFAOYSA-M

|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

|InChIKey = HEMHJVSKTPXQMS-REWHXWOFAM

| Section2 = {{Chembox Properties

|Formula = NaOH

|MolarMass = 39.9971 g/mol

|Appearance = White, opaque crystals

|Odor = odorless

|Density = 2.13 g/cm³<ref name="crc">Haynes, p. 4.90</ref>

|MeltingPtC = 323

|MeltingPt_ref=<ref name="crc" />

|BoilingPtC = 1388

|BoilingPt_ref=<ref name="crc" />

|Solubility = 418 g/L (0&nbsp;°C)<br />1000 g/L (25&nbsp;°C)<ref name="crc" /><br />3370 g/L (100&nbsp;°C)

|Solvent1 = methanol

|Solubility1 = 238 g/L

|Solvent2 = ethanol

|Solubility2 = <<139 g/L

|SolubleOther = soluble in [[glycerol]], negligible in [[ammonia]], insoluble in [[diethyl ether|ether]], slowly soluble in [[propylene glycol]]

|VaporPressure = <2.4 kPa (20&nbsp;°C)<br>0.1 kPa (700&nbsp;°C)

|pKa = 15.7

|RefractIndex = 1.3576

|MagSus = −15.8·10⁻⁶ cm³/mol (aq.)<ref>Haynes, p. 4.135</ref>

| Section3 = {{Chembox Structure

|Structure_ref =<ref>{{cite journal|doi=10.1002/zaac.19855311217|title=Hydroxide des Natriums, Kaliums und Rubidiums: Einkristallzüchtung und röntgenographische Strukturbestimmung an der bei Raumtemperatur stabilen Modifikation|author=Jacobs, H.; Kockelkorn, J. and Tacke, Th. |journal=Z. Anorg. Allg. Chem.|year=1985|volume=531|issue=12 |pages=119–124}}</ref>

|CrystalStruct = Orthorhombic, [[Pearson symbol|oS8]]

|SpaceGroup = Cmcm, No. 63

|LattConst_a = 0.34013 nm

|LattConst_b = 1.1378 nm

|LattConst_c = 0.33984 nm

| UnitCellFormulas = 4

| Section4 = {{Chembox Thermochemistry

|Thermochemistry_ref=<ref>Haynes, p. 5.13</ref>

|DeltaHf = −425.8 kJ/mol

|DeltaGf = -379.7 kJ/mol

|Entropy = 64.4 J/(mol·K)

|HeatCapacity = 59.5 J/(mol·K)

| Section5 = {{Chembox Hazards

|ExternalSDS = [http://www.certified-lye.com/SDS-Lye.pdf External SDS]

|GHSPictograms = {{GHS05}} {{GHS07}}

|GHSSignalWord = '''Danger'''

|HPhrases = {{H-phrases|290|302|314}}

|PPhrases = {{P-phrases|280|305+351+338|310}}

|NFPA-H = 3

|NFPA-F = 0

|NFPA-R = 1

|NFPA-S = ALK

|LD50 = 40 mg/kg (mouse, intraperitoneal)<ref>Michael Chambers. [https://chem.nlm.nih.gov/chemidplus/rn/1310-73-2 "ChemIDplus – 1310-73-2 – HEMHJVSKTPXQMS-UHFFFAOYSA-M – Sodium hydroxide [NF<nowiki>]</nowiki> – Similar structures search, synonyms, formulas, resource links, and other chemical information."]. ''nih.gov''.</ref><br>140 - 340 mg/kg (rat, oral)<br>1350 mg/kg (rabbit, dermal)

|PEL = TWA 2 mg/m³<ref name="PGCH">{{PGCH|0565}}</ref>

|IDLH = 10 mg/m³<ref name="PGCH" />

|REL = C 2 mg/m³<ref name="PGCH" />

|LDLo = 500 mg/kg (rabbit, oral)<ref>{{IDLH|1310732|Sodium hydroxide}}</ref>

| Section6 = {{Chembox Related

|OtherAnions = {{ubl|[[Sodium hydrosulfide]]|[[Sodium hydride]]|[[Sodium oxide]]}}

|OtherCations = {{ubl|[[Lithium hydroxide]]|[[Potassium hydroxide]]|[[Rubidium hydroxide]]|[[Caesium hydroxide]]|[[Francium hydroxide]]}}

|OtherCompounds = {{ubl|[[Sodium deuteroxide]]|[[Sodium hypochlorite|Sodium chloroxide]]}}

}}

}}

'''Sodium hydroxide''', also known as '''lye''' and '''caustic soda''',<ref name="msd">{{cite web|title=Material Safety Datasheet|url=http://www.certified-lye.com/MSDS-Lye.pdf|work=certified-lye.com|access-date=2010-02-24|archive-date=2008-02-28|archive-url=https://web.archive.org/web/20080228005947/http://www.certified-lye.com/MSDS-Lye.pdf|url-status=dead}}</ref><ref name="msd2">{{cite web|title=Material Safety Datasheet 2|url=http://www.hillbrothers.com/msds/pdf/sodium-hydroxide-10-50-liq.pdf|work=hillbrothers.com|access-date=2012-05-20|archive-url=https://web.archive.org/web/20120803005424/http://www.hillbrothers.com/msds/pdf/sodium-hydroxide-10-50-liq.pdf|archive-date=2012-08-03|url-status=dead}}</ref> is an [[inorganic compound]] with the formula {{chem2|NaOH}}. It is a white solid [[ionic compound]] consisting of [[sodium]] [[cation]]s {{chem2|Na+}} and [[hydroxide]] [[anion]]s {{chem2|OH−}}.

Sodium hydroxide is a highly [[corrosive]] [[base (chemistry)|base]] and [[alkali]] that decomposes [[lipid]]s and [[protein]]s at ambient [[temperature]]s and may cause severe [[chemical burn]]s. It is highly soluble in [[water]], and readily absorbs [[moisture]] and [[carbon dioxide]] from the [[air]]. It forms a series of [[hydrate]]s {{chem2|NaOH*''n''H2O}}.<ref name="siem" /> The monohydrate {{chem2|NaOH*H2O}} crystallizes from water solutions between 12.3 and 61.8&nbsp;°C. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of the [[anhydrous]] compound.

As one of the simplest hydroxides, sodium hydroxide is frequently used alongside neutral [[water]] and acidic [[hydrochloric acid]] to demonstrate the pH scale to chemistry students.<ref>{{cite web | url=https://www.orf.od.nih.gov/EnvironmentalProtection/WasteDisposal/Pages/Examples+of+Common+Laboratory+ChemicalsandtheirHazardClass.aspx | title=Examples of Common Laboratory Chemicals and their Hazard Class | access-date=2018-01-09 | archive-date=2018-01-10 | archive-url=https://web.archive.org/web/20180110054910/https://www.orf.od.nih.gov/EnvironmentalProtection/WasteDisposal/Pages/Examples+of+Common+Laboratory+ChemicalsandtheirHazardClass.aspx | url-status=dead }}</ref>

Sodium hydroxide is used in many industries: in the making of [[wood pulp]] and [[paper]], [[textile]]s, [[drinking water]], [[soap]]s and [[detergent]]s, and as a [[chemical drain cleaners#Alkaline drain openers|drain cleaner]]. Worldwide production in 2004 was approximately 60&nbsp;million tons, while demand was 51&nbsp;million tons.<ref name="Ullmann"/>

==Properties==

===Physical properties===

Pure sodium hydroxide is a colorless crystalline solid that melts at {{convert|318|C|F}} without decomposition and boils at {{convert|1388|C|F}}. It is highly soluble in water, with a lower solubility in [[Chemical polarity|polar]] [[solvent]]s such as [[ethanol]] and [[methanol]].<ref name="Protank-2018">{{cite news|url=https://www.protank.com/sodium-hydroxide|title=Sodium Hydroxide Storage Tanks & Specifications|date=2018-09-08|work=Protank|access-date=2018-11-21|language=en-US}}</ref> Sodium hydroxide is insoluble in [[ether]] and other non-polar solvents.

Similar to the hydration of sulfuric acid, [[dissolution (chemistry)|dissolution]] of solid sodium hydroxide in water is a highly [[exothermic reaction]]<ref>{{cite web |last=<!-- not stated --> |date=August 29, 2014 |title=Exothermic vs. Endothermic: Chemistry's Give and Take |url=https://www.discoveryexpresskids.com/blog/exothermic-vs-endothermic-chemistrys-give-and-take |access-date=March 28, 2023 |website=Discovery Express Kids |archive-date=March 28, 2023 |archive-url=https://web.archive.org/web/20230328171940/https://www.discoveryexpresskids.com/blog/exothermic-vs-endothermic-chemistrys-give-and-take |url-status=dead }}</ref> where a large amount of heat is liberated, posing a threat to safety through the possibility of splashing. The resulting solution is usually colorless and odorless. As with other alkaline solutions, it feels slippery with skin contact due to the process of [[saponification]] that occurs between {{chem2|NaOH}} and natural skin oils.

==== Viscosity ====

Concentrated (50%) aqueous solutions of sodium hydroxide have a characteristic [[viscosity]], 78 m[[Pascal (unit)|Pa]]·s, that is much greater than that of water (1.0 mPa·s) and near that of olive oil (85 mPa·s) at room temperature. The viscosity of aqueous {{chem2|NaOH}}, as with any liquid chemical, is inversely related to its temperature, i.e., its viscosity decreases as temperature increases, and vice versa. The viscosity of sodium hydroxide solutions plays a direct role in its application as well as its storage.<ref name="Protank-2018" />

====Hydrates====

Sodium hydroxide can form several hydrates {{chem2|NaOH*''n''H2O}}, which result in a complex solubility diagram that was described in detail by [[Spencer Umfreville Pickering]] in 1893.<ref name="pick">{{cite journal | last1 = Umfreville Pickering | first1 = Spencer | year = 1893 | title = LXI.—The hydrates of sodium, potassium, and lithium hydroxides | url = https://zenodo.org/record/1860180| journal = Journal of the Chemical Society, Transactions | volume = 63 | issue = | pages = 890–909 | doi = 10.1039/CT8936300890 }}</ref> The known hydrates and the approximate ranges of temperature and concentration (mass percent of NaOH) of their [[Saturated solution|saturated]] water solutions are:<ref name="siem" />

* Heptahydrate, {{chem2|NaOH*7H2O}}: from −28&nbsp;°C (18.8%) to −24&nbsp;°C (22.2%).<ref name="pick" />

* Pentahydrate, {{chem2|NaOH*5H2O}}: from −24&nbsp;°C (22.2%) to −17.7&nbsp;°C (24.8%).<ref name="pick" />

* Tetrahydrate, {{chem2|NaOH*4H2O}}, α form: from −17.7&nbsp;°C (24.8%) to 5.4&nbsp;°C (32.5%).<ref name="pick" /><ref name="mrawIII">{{cite journal | last1 = Mraw | first1 = S. C. | last2 = Giauque | first2 = W. F. | year = 1974 | title = Entropies of the hydrates of sodium hydroxide. III. Low-temperature heat capacities and heats of fusion of the α and β crystalline forms of sodium hydroxide tetrahydrate | url = | journal = Journal of Physical Chemistry | volume = 78 | issue = 17| pages = 1701–1709 | doi = 10.1021/j100610a005 }}</ref>

* Tetrahydrate, {{chem2|NaOH*4H2O}}, β form: metastable.<ref name="pick" /><ref name="mrawIII" />

* Trihemihydrate, {{chem2|NaOH*3.5H2O}}: from 5.4&nbsp;°C (32.5%) to 15.38&nbsp;°C (38.8%) and then to 5.0&nbsp;°C (45.7%).<ref name="pick" /><ref name="siem" />

* Trihydrate, {{chem2|NaOH*3H2O}}: metastable.<ref name="pick" />

* Dihydrate, {{chem2|NaOH*2H2O}}: from 5.0&nbsp;°C (45.7%) to 12.3&nbsp;°C (51%).<ref name="pick" /><ref name="siem">{{cite journal | last1 = Siemens | first1 = P. R. | last2 = Giauque | first2 = William F. | year = 1969 | title = Entropies of the hydrates of sodium hydroxide. II. Low-temperature heat capacities and heats of fusion of NaOH·2H2O and NaOH·3.5H2O | url = | journal = Journal of Physical Chemistry | volume = 73 | issue = 1| pages = 149–157 | doi = 10.1021/j100721a024 }}</ref>

* Monohydrate, {{chem2|NaOH*H2O}}: from 12.3&nbsp;°C (51%) to 65.10&nbsp;°C (69%) then to 62.63&nbsp;°C (73.1%).<ref name="pick" /><ref name="murch">{{cite journal | last1 = Murch | first1 = L. E. | last2 = Giauque | first2 = W. F. | year = 1962 | title = The thermodynamic properties of sodium hydroxide and its monohydrate. Heat capacities to low temperatures. Heats of solution | url = | journal = Journal of Physical Chemistry | volume = 66 | issue = 10| pages = 2052–2059 | doi = 10.1021/j100816a052 }}</ref>

Early reports refer to hydrates with ''n'' = 0.5 or ''n'' = 2/3, but later careful investigations failed to confirm their existence.<ref name="murch" />

The only hydrates with stable melting points are {{chem2|NaOH*H2O}} (65.10&nbsp;°C) and {{chem2|NaOH*3.5H2O}} (15.38&nbsp;°C). The other hydrates, except the metastable ones {{chem2|NaOH*3H2O}} and {{chem2|NaOH*4H2O}} (β) can be crystallized from solutions of the proper composition, as listed above. However, solutions of NaOH can be easily supercooled by many degrees, which allows the formation of hydrates (including the metastable ones) from solutions with different concentrations.<ref name="siem" /><ref name="murch" />

For example, when a solution of NaOH and water with 1:2 mole ratio (52.6% NaOH by mass) is cooled, the monohydrate normally starts to crystallize (at about 22&nbsp;°C) before the dihydrate. However, the solution can easily be supercooled down to −15&nbsp;°C, at which point it may quickly crystallize as the dihydrate. When heated, the solid dihydrate might melt directly into a solution at 13.35&nbsp;°C; however, once the temperature exceeds 12.58&nbsp;°C it often decomposes into solid monohydrate and a liquid solution. Even the ''n'' = 3.5 hydrate is difficult to crystallize, because the solution supercools so much that other hydrates become more stable.<ref name="siem" />

A hot water solution containing 73.1% (mass) of NaOH is a [[eutectic]] that solidifies at about 62.63&nbsp;°C as an intimate mix of anhydrous and monohydrate crystals.<ref name="brodale">{{cite journal | last1 = Brodale | first1 = G. E. | last2 = Giauque | first2 = W. F. | year = 1962 | title = The freezing point-solubility curve of aqueous sodium hydroxide in the region near the anhydrous-monohydrate eutectic | url = | journal = Journal of Physical Chemistry | volume = 66 | issue = 10| pages = 2051 | doi = 10.1021/j100816a051}}</ref><ref name="murch" />

A second stable eutectic composition is 45.4% (mass) of NaOH, that solidifies at about 4.9&nbsp;°C into a mixture of crystals of the dihydrate and of the 3.5-hydrate.<ref name="siem" />

The third stable eutectic has 18.4% (mass) of NaOH. It solidifies at about −28.7&nbsp;°C as a mixture of water ice and the heptahydrate {{chem2|NaOH*7H2O}}.<ref name="pick" /><ref name="conde">M. Conde Engineering: "[http://www.aldacs.com/DocBase/AqNaOHSLEVLE.pdf Solid-Liquid Equilibrium (SLE) and Vapour-Liquid Equilibrium (VLE) of Aqueous NaOH] {{Webarchive|url=https://web.archive.org/web/20201007122113/http://www.aldacs.com/DocBase/AqNaOHSLEVLE.pdf |date=2020-10-07 }}". Online report, accessed on 2017-04-29.</ref>

When solutions with less than 18.4% NaOH are cooled, water [[ice]] crystallizes first, leaving the NaOH in solution.<ref name="pick" />

The α form of the tetrahydrate has density 1.33 g/cm³. It melts congruously at 7.55&nbsp;°C into a liquid with 35.7% NaOH and density 1.392 g/cm³, and therefore floats on it like ice on water. However, at about 4.9&nbsp;°C it may instead melt incongruously into a mixture of solid {{chem2|NaOH*3.5H2O}} and a liquid solution.<ref name="mrawIII" />

The β form of the tetrahydrate is metastable, and often transforms spontaneously to the α form when cooled below −20&nbsp;°C.<ref name="mrawIII" /> Once initiated, the exothermic transformation is complete in a few minutes, with a 6.5% increase in volume of the solid. The β form can be crystallized from supercooled solutions at −26&nbsp;°C, and melts partially at −1.83&nbsp;°C.<ref name="mrawIII" />

The "sodium hydroxide" of commerce is often the monohydrate (density 1.829 g/cm³). Physical data in technical literature may refer to this form, rather than the anhydrous compound.

====Crystal structure====

NaOH and its monohydrate form orthorhombic crystals with the space groups Cmcm ([[Pearson symbol|oS8]]) and Pbca (oP24), respectively. The monohydrate cell dimensions are a = 1.1825, b = 0.6213, c = 0.6069 [[nanometer|nm]]. The atoms are arranged in a [[hydrargillite]]-like layer structure, with each sodium atom surrounded by six oxygen atoms, three each from hydroxide ions and three from water molecules. The hydrogen atoms of the hydroxyls form strong bonds with oxygen atoms within each O layer. Adjacent O layers are held together by [[hydrogen bond]]s between water molecules.<ref name="jacobs">{{cite journal|author=Jacobs, H. and Metzner, U. |year=1991|title=Ungewöhnliche H-Brückenbindungen in Natriumhydroxidmonohydrat: Röntgen- und Neutronenbeugung an NaOH·H<sub">2</sub">O bzw. NaOD·D<sub">2</sub">O|journal=Zeitschrift für anorganische und allgemeine Chemie|volume =597| issue =1| pages =97–106|doi=10.1002/zaac.19915970113}}</ref>

===Chemical properties===

====Reaction with acids====

Sodium hydroxide reacts with protic acids to produce water and the corresponding salts. For example, when sodium hydroxide reacts with [[hydrochloric acid]], [[sodium chloride]] is formed:

:{{chem2|NaOH(aq) + HCl(aq) -> NaCl(aq) + H2O(l)}}

In general, such [[neutralization (chemistry)|neutralization]] reactions are represented by one simple net ionic equation:

:{{chem2|OH-(aq) + H+(aq) -> H2O(l)}}

This type of reaction with a strong acid releases heat, and hence is [[exothermic reaction|exothermic]]. Such [[acid–base reaction]]s can also be used for [[titration]]s. However, sodium hydroxide is not used as a [[primary standard]] because it is [[hygroscopic]] and absorbs [[carbon dioxide]] from air.

====Reaction with acidic oxides====

Sodium hydroxide also reacts with [[acid anhydride|acidic oxides]], such as [[sulfur dioxide]]. Such reactions are often used to "[[Scrubber|scrub]]" harmful acidic gases (like {{chem2|SO2}} and {{chem2|H2S}}) produced in the burning of coal and thus prevent their release into the atmosphere. For example,

:{{chem2|2 NaOH + SO2 → Na2SO3 + H2O}}

====Reaction with metals and oxides====

Glass reacts slowly with aqueous sodium hydroxide solutions at ambient temperatures to form soluble [[silicate]]s. Because of this, glass joints and [[stopcock]]s exposed to sodium hydroxide have a tendency to "freeze". [[Laboratory flask|Flask]]s and glass-lined [[chemical reactor]]s are damaged by long exposure to hot sodium hydroxide, which also frosts the glass. Sodium hydroxide does not attack [[iron]] at room temperature, since iron does not have [[amphoteric]] properties (i.e., it only dissolves in acid, not base).

Nevertheless, at high temperatures (e.g. above 500&nbsp;°C), iron can react [[endothermic]]ally with sodium hydroxide to form [[iron(III) oxide]], [[sodium]] metal, and [[hydrogen]] gas.<ref>{{Citation |last=祖恩 |first=许 |title=钾素,钾肥溯源[J] |date=1992}}</ref> This is due to the lower [[enthalpy of formation]] of iron(III) oxide (−824.2 kJ/mol) compared to sodium hydroxide (−500 kJ/mol) and positive entropy change of the reaction, which implies spontaneity at high temperatures ({{nowrap|ΔST > ΔH}}, {{nowrap|ΔG < 0}}) and non-spontaneity at low temperatures ({{nowrap|ΔST < ΔH}}, {{nowrap|ΔG > 0}}). Consider the following reaction between molten sodium hydroxide and finely divided iron filings:

:{{chem2|4 Fe + 6 NaOH → 2 Fe2O3 + 6 Na + 3 H2}}

A few [[transition metal]]s, however, may react quite vigorously with sodium hydroxide under milder conditions.

In 1986, an aluminium [[tank truck|road tanker]] in the UK was mistakenly used to transport 25% sodium hydroxide solution,<ref>{{Citation |last=Stamell |first=Jim |title=EXCEL HSC Chemistry |pages=199 |publisher=Pascal Press |date=2001 |isbn=978-1-74125-299-6}}</ref> causing pressurization of the contents and damage to tankers. The pressurization is due to the hydrogen gas which is produced in the reaction between sodium hydroxide and aluminium:

:{{chem2|2 Al + 2 NaOH + 6 H2O → 2 Na[Al(OH)4] + 3 H2}}

====Precipitant====

Unlike sodium hydroxide, which is soluble, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used to [[precipitate]] transition metal hydroxides. The following colours are observed:

* Copper - blue

* Iron(II) - green

* Iron(III) - yellow / brown

Zinc and lead salts dissolve in excess sodium hydroxide to give a clear solution of {{chem2|Na2ZnO2}} or {{chem2|Na2PbO2}}.

[[Aluminium hydroxide]] is used as a gelatinous [[Flocculation#Flocculants|flocculant]] to filter out particulate matter in [[water treatment]]. Aluminium hydroxide is prepared at the treatment plant from [[aluminium sulfate]] by reacting it with sodium hydroxide or bicarbonate.

:{{chem2|Al2(SO4)3 + 6 NaOH → 2 Al(OH)3 + 3 Na2SO4}}

:{{chem2|Al2(SO4)3 + 6 NaHCO3 → 2 Al(OH)3 + 3 Na2SO4 + 6 CO2}}

====Saponification====

Sodium hydroxide can be used for the base-driven [[hydrolysis of esters]] (also called [[saponification]]), [[amide]]s and [[alkyl halide]]s.<ref name="Protank-2018" /> However, the limited solubility of sodium hydroxide in organic solvents means that the more [[soluble]] [[potassium hydroxide]] (KOH) is often preferred. Touching a sodium hydroxide solution with bare hands, while not recommended, produces a slippery feeling. This happens because oils on the skin such as [[sebum]] are converted to soap.

Despite solubility in [[propylene glycol]] it is unlikely to replace water in saponification due to propylene glycol's primary reaction with fat before reaction between sodium hydroxide and fat.

{| class="wikitable"

! scope="row" | Mass fraction of NaOH (wt%)

! scope="col" | 4

! scope="col" | 10

! scope="col" | 20

! scope="col" | 30

! scope="col" | 40

! scope="col" | 50

|-

! scope="row" | Molar concentration of NaOH (M)

|1.04

|2.77

|6.09

|9.95

|14.30

|19.05

|-

! scope="row" | Mass concentration of NaOH (g/L)

|41.7

|110.9

|243.8

|398.3

|572.0

|762.2

|-

! scope="row" | Density of solution (g/mL)

|1.043

|1.109

|1.219

|1.328

|1.430

|1.524

|}

==Production==

{{for|historical information|Alkali manufacture}}

Sodium hydroxide is industrially produced as a 50% solution by variations of the electrolytic [[chloralkali process]].<ref name="Du">{{cite journal | doi = 10.1021/acs.est.8b01195 | pmid = 29669210 | title = Sodium hydroxide production from seawater desalination brine: process design and energy efficiency | author = Fengmin Du, David M Warsinger, Tamanna I Urmi, Gregory P Thiel, Amit Kumar, John H Lienhard | journal = Environmental Science & Technology | volume = 52 | issue = 10 | pages = 5949–5958 | date = 2018 | bibcode = 2018EnST...52.5949D | hdl = 1721.1/123096 | hdl-access = free}}</ref> [[Chlorine gas]] is also produced in this process.<ref name="Du"/> Solid sodium hydroxide is obtained from this solution by the evaporation of water. Solid sodium hydroxide is most commonly sold as flakes, [[prill]]s, and cast blocks.<ref name="Ullmann"/>

In 2004, world production was estimated at 60 million dry tonnes of sodium hydroxide, and demand was estimated at 51&nbsp;million tonnes.<ref name="Ullmann">{{Ullmann | doi = 10.1002/14356007.a24_345.pub2 | title = Sodium Hydroxide | author = Cetin Kurt, Jürgen Bittner | }}</ref> In 1998, total world production was around 45&nbsp;million [[tonne]]s. North America and Asia each contributed around 14&nbsp;million tonnes, while Europe produced around 10&nbsp;million tonnes. In the United States, the major producer of sodium hydroxide is [[Olin Corporation|Olin]], which has annual production around 5.7&nbsp;million [[tonne]]s from sites at [[Freeport, Texas]]; [[Plaquemine, Louisiana]]; [[St. Gabriel, Louisiana]]; [[McIntosh, Alabama]]; [[Charleston, Tennessee]]; [[Niagara Falls, New York]]; and [[Bécancour, Quebec|Bécancour, Canada]]. Other major US producers include [[Oxychem]], [[PPG Industries|Westlake]], Shintek, and [[Formosa Plastics Group|Formosa]]. All of these companies use the [[chloralkali process]].<ref name="Kirk">[http://www.mrw.interscience.wiley.com/kirk/kirk_articles_fs.html ''Kirk-Othmer Encyclopedia of Chemical Technology'']{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes}}, 5th edition, John Wiley & Sons</ref>

Historically, sodium hydroxide was produced by treating [[sodium carbonate]] with [[calcium hydroxide]] (slaked lime) in a [[Salt metathesis reaction|metathesis reaction]] which takes advantage of the fact that sodium hydroxide is soluble, while calcium carbonate is not. This process was called causticizing.<ref>{{cite book |last1= Deming|first1=Horace G. |title=General Chemistry: An Elementary Survey Emphasizing Industrial Applications of Fundamental Principles |edition=2nd |year=1925 |publisher=John Wiley & Sons, Inc. |location=New York |page=452 }}</ref>

:{{chem2|Ca(OH)2(aq) + Na2CO3(s) → CaCO3(s) + 2 NaOH(aq)}}

The sodium carbonate for this reaction was produced by the [[Leblanc process]] in the early 19th century, or the [[Solvay process]] in the late 19th century. The conversion of sodium carbonate to sodium hydroxide was superseded entirely by the [[chloralkali process]], which produces sodium hydroxide in a single process.

Sodium hydroxide is also produced by combining pure sodium metal with water. The byproducts are hydrogen gas and heat, often resulting in a flame.

:{{chem2|2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)}}

This reaction is commonly used for demonstrating the reactivity of alkali metals in academic environments; however, it is not used commercially aside from a reaction within the [[Chloralkali process#Mercury cell|mercury cell chloralkali process]] where [[sodium amalgam]] is reacted with water.

==Uses==

{{see also|Hydrodesulfurization}}Sodium hydroxide is a popular strong [[base (chemistry)|base]] used in industry. Sodium hydroxide is used in the manufacture of sodium salts and detergents, pH regulation, and organic synthesis. In bulk, it is most often handled as an [[aqueous solution]],<ref>{{cite web|url=http://www.ppg.com/chemicals/chloralkali/products/Documents/CausticSodamanual2008.pdf|title=Document 2 - CausticSodamanual2008.pdf|year=2013|access-date=July 17, 2014|archive-date=March 19, 2015|archive-url=https://web.archive.org/web/20150319003215/http://www.ppg.com/chemicals/chloralkali/products/Documents/CausticSodamanual2008.pdf|url-status=dead}}</ref> since solutions are cheaper and easier to handle.

Sodium hydroxide is used in many scenarios where it is desirable to increase the [[alkalinity]] of a mixture, or to neutralize acids. For example, in the petroleum industry, sodium hydroxide is used as an additive in [[drilling mud]] to increase [[alkalinity]] in [[bentonite]] mud systems, to increase the mud [[viscosity]], and to neutralize any [[acid gas]] (such as [[hydrogen sulfide]] and [[carbon dioxide]]) which may be encountered in the [[geological formation]] as drilling progresses. Another use is in [[salt spray test]]ing where pH needs to be regulated. Sodium hydroxide is used with hydrochloric acid to balance pH. The resultant salt, NaCl, is the corrosive agent used in the standard neutral pH salt spray test.

Poor quality [[crude oil]] can be treated with sodium hydroxide to remove [[sulfur]]ous impurities in a process known as ''caustic washing''. Sodium hydroxide reacts with weak acids such as [[hydrogen sulfide]] and [[mercaptans]] to yield non-volatile sodium salts, which can be removed. The waste which is formed is toxic and difficult to deal with, and the process is banned in many countries because of this. In 2006, [[Trafigura]] used the process and then [[2006 Côte d'Ivoire toxic waste dump|dumped the waste in Ivory Coast]].<ref name="Guardian">{{cite news|url=https://www.theguardian.com/environment/2009/sep/16/trafigura-case-toxic-slop|title=Trafigura case: toxic slop left behind by caustic washing|last=Sample|first=Ian|date=16 September 2009 |newspaper=The Guardian|access-date=2009-09-17}}</ref><ref name="bbc">{{cite news|url=http://news.bbc.co.uk/1/hi/programmes/newsnight/8259765.stm|title=Trafigura knew of waste dangers|date=16 September 2009|publisher=BBC Newsnight|access-date=2009-09-17}}</ref>

Other common uses of sodium hydroxide include:

* for making soaps and detergents. Sodium hydroxide is used for hard bar soap, while [[potassium hydroxide]] is used for liquid soaps.<ref>{{cite web|title=A Guide to Caustic Chemicals Used in Soap Making {{!}} Brenntag|url=https://www.brenntag.com/en-us/industries/household-industrial-institutional/chemicals-in-liquid-soap/|access-date=2020-10-03|website=www.brenntag.com|language=en}}</ref><ref>{{cite web|date=2016-09-06|title=Sodium Hydroxide {{!}} Uses, Benefits, and Chemical Safety Facts|url=https://www.chemicalsafetyfacts.org/sodium-hydroxide/|access-date=2020-10-03|website=ChemicalSafetyFacts.org|language=en-US}}</ref> Sodium hydroxide is used more often than [[potassium hydroxide]] because it is cheaper and a smaller quantity is needed.

* as drain cleaners that convert pipe-clogging fats and grease into soap, which dissolves in water

* for making artificial textile fibres such as [[rayon]]

* in the manufacture of [[paper]]. Around 56% of sodium hydroxide produced is used by industry, 25% of which is used in the paper industry.

* in purifying [[Bauxite|bauxite ore]] from which [[aluminium]] metal is extracted. This is known as the [[Bayer process]].

* de-greasing metals

* [[oil refining]]

* making [[dye]]s and [[bleach]]es

* in water treatment plants for pH regulation

* to treat bagels and pretzel dough, giving the distinctive shiny finish

===Chemical pulping===

{{main|Pulp (paper)}}

Sodium hydroxide is also widely used in pulping of wood for making paper or regenerated fibers. Along with [[sodium sulfide]], sodium hydroxide is a key component of the white liquor solution used to separate [[lignin]] from [[cellulose]] [[fiber]]s in the [[kraft process]]. It also plays a key role in several later stages of the process of [[Bleaching of wood pulp|bleaching the brown pulp]] resulting from the pulping process. These stages include [[oxygen]] delignification, [[oxidation|oxidative]] extraction, and simple extraction, all of which require a strong alkaline environment with a pH > 10.5 at the end of the stages.

===Tissue digestion===

In a similar fashion, sodium hydroxide is used to digest tissues, as in a process that was used with farm animals at one time. This process involved placing a carcass into a sealed chamber, then adding a mixture of sodium hydroxide and water (which breaks the chemical bonds that keep the flesh intact). This eventually turns the body into a liquid with a dark brown color,<ref name="Ayres">Ayres, Chris (27 February 2010) [http://www.thetimes.co.uk/tto/news/world/americas/article2002276.ece Clean green finish that sends a loved one down the drain] Times Online. Retrieved 2013-02-20.</ref><ref name="carcassdisposal">Thacker, H. Leon; Kastner, Justin (August 2004). [https://krex.k-state.edu/dspace/bitstream/handle/2097/662/Chapter6.pdf ''Carcass Disposal: A Comprehensive Review. Chapter 6''] {{Webarchive|url=https://web.archive.org/web/20170202034816/https://krex.k-state.edu/dspace/bitstream/handle/2097/662/Chapter6.pdf |date=2017-02-02 }}. National Agricultural Biosecurity Center, Kansas State University, 2004. Retrieved 2010-03-08</ref> and the only solids that remain are bone hulls, which can be crushed between one's fingertips.<ref name="Roach">Roach, Mary (2004). ''Stiff: The Curious Lives of Human Cadavers'', New York: W.W. Norton & Company. {{ISBN|0-393-32482-6}}.</ref>

Sodium hydroxide is frequently used in the process of decomposing [[roadkill]] dumped in landfills by animal disposal contractors.<ref name="carcassdisposal" /> Due to its availability and low cost, it has been used by criminals to dispose of corpses. Italian [[serial killer]] [[Leonarda Cianciulli]] used this chemical to turn dead bodies into soap.<ref>{{cite news |url= https://www.bbc.co.uk/news/magazine-27257822 |title= Sodium:Getting rid of dirt – and murder victims |date= 3 May 2014 |work= [[BBC News]]}}</ref> In Mexico, a man who worked for drug cartels admitted disposing of over 300 bodies with it.<ref>{{cite news | url = https://www.washingtonpost.com/wp-dyn/content/article/2009/01/26/AR2009012602190.html | author = William Booth | title = 'Stewmaker' Stirs Horror in Mexico | newspaper = [[Washington Post]] | date = January 27, 2009}}</ref>

Sodium hydroxide is a dangerous chemical due to its ability to hydrolyze protein. If a dilute solution is spilled on the skin, burns may result if the area is not washed thoroughly and for several minutes with running water. Splashes in the eye can be more serious and can lead to blindness.<ref>{{cite web|url=http://www.atsdr.cdc.gov/MMG/MMG.asp?id=246&tid=45|archive-url=https://web.archive.org/web/20100528070612/http://www.atsdr.cdc.gov/MMG/MMG.asp?id=246&tid=45|url-status=dead|archive-date=May 28, 2010|title=ATSDR – Medical Management Guidelines (MMGs): Sodium Hydroxide|website=www.atsdr.cdc.gov}}</ref>

===Dissolving amphoteric metals and compounds===

Strong bases attack [[aluminium]]. Sodium hydroxide reacts with aluminium and water to release hydrogen gas. The aluminium takes an oxygen atom from sodium hydroxide, which in turn takes an oxygen atom from water, and releases two hydrogen atoms. The reaction thus produces [[hydrogen]] gas and [[sodium aluminate]]. In this reaction, sodium hydroxide acts as an agent to make the solution alkaline, which aluminium can dissolve in.

:{{chem2|2 Al + 2 }} {{chem2|NaOH + 2 H2O}} → 2 {{chem2| NaAlO2}} + {{chem2|3 H2}}

Sodium aluminate is an inorganic chemical that is used as an effective source of [[aluminium hydroxide]] for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as {{chem2|NaAlO2}}, {{chem2|Na3AlO3}}, {{chem2|Na[Al(OH)4]}}, {{chem2|Na2O*Al2O3}} or {{chem2|Na2Al2O4}}. Formation of sodium tetrahydroxoaluminate(III) or hydrated sodium aluminate is given by:<ref>{{cite web|last=PubChem|title=Aluminium sodium tetrahydroxide|url=https://pubchem.ncbi.nlm.nih.gov/compound/166673|access-date=2020-10-03|website=pubchem.ncbi.nlm.nih.gov|language=en}}</ref>

:{{chem2|2 Al + 2 NaOH + 6 H2}}O {{chem2|→ 2 Na[Al(OH)4] + 3 H2}}

This reaction can be useful in [[etching]], removing anodizing, or converting a polished surface to a satin-like finish, but without further [[Passivation (chemistry)|passivation]] such as [[anodizing]] or [[alodining]] the surface may become degraded, either under normal use or in severe atmospheric conditions.

In the [[Bayer process]], sodium hydroxide is used in the refining of alumina containing ores ([[bauxite]]) to produce alumina ([[aluminium oxide]]) which is the raw material used to produce aluminium via the [[electrolysis|electrolytic]] [[Hall-Héroult process]]. Since the alumina is [[amphoteric]], it dissolves in the sodium hydroxide, leaving impurities less soluble at high [[pH]] such as [[iron oxides]] behind in the form of a highly alkaline [[red mud]].

Other amphoteric metals are zinc and lead which dissolve in concentrated sodium hydroxide solutions to give [[sodium zincate]] and [[sodium plumbate]] respectively.

===Esterification and transesterification reagent===

Sodium hydroxide is traditionally used in soap making ([[cold process]] soap, [[saponification]]).<ref name="Morfit">{{cite book|title =A treatise on chemistry applied to the manufacture of soap and candles|first= Campbell|last=Morfit|author-link=Campbell Morfit|publisher=Parry and McMillan|year = 1856|url =https://archive.org/details/atreatiseonchem00morfgoog}}</ref> It was made in the nineteenth century for a hard surface rather than liquid product because it was easier to store and transport.

For the manufacture of [[biodiesel]], sodium hydroxide is used as a [[catalyst]] for the [[transesterification]] of methanol and triglycerides. This only works with [[anhydrous]] sodium hydroxide, because combined with water the fat would turn into [[soap]], which would be tainted with [[methanol]]. NaOH is used more often than [[potassium hydroxide]] because it is cheaper and a smaller quantity is needed. Due to production costs, NaOH, which is produced using common salt is cheaper than potassium hydroxide.<ref>{{cite web|title=Side by Side Comparison: Potassium Hydroxide and Sodium Hydroxide - Similarities, Differences and Use Cases|url=https://info.noahtech.com/blog/sicomparison-potassium-hydroxide-and-sodium-hydroxide|access-date=2020-10-03|website=info.noahtech.com|language=en-us|archive-date=2020-10-10|archive-url=https://web.archive.org/web/20201010090833/https://info.noahtech.com/blog/sicomparison-potassium-hydroxide-and-sodium-hydroxide|url-status=dead}}</ref>

===Skincare ingredient===

Sodium hydroxide is an ingredient used in some [[Skin care|skincare]] and [[Cosmetics|cosmetic]] products, such as facial cleansers, creams, lotions, and makeup. It is typically used in low concentration as a [[PH|pH balancer]], due its highly alkaline nature.<ref>{{cite web |url= https://www.cir-safety.org/sites/default/files/inorganic%20hydroxides.pdf |title= Safety Assessment of Inorganic Hydroxides as Used in Cosmetics |work=cir-safety.org | year=2015 |access-date=May 12, 2024}}</ref>

===Food preparation===

Food uses of sodium hydroxide include washing or chemical peeling of [[fruits]] and [[vegetables]], [[chocolate]] and [[Cocoa mass|cocoa]] processing, [[caramel coloring]] production, [[poultry]] scalding, [[soft drink]] processing, and thickening [[ice cream]].<ref>{{cite web |url= http://www.rsc.org/chemistryworld/podcast/CIIEcompounds/transcripts/NaOH.asp |title=Sodium Hydroxide |work=rsc.org | year=2014 |access-date=November 9, 2014}}</ref> [[Olive]]s are often soaked in sodium hydroxide for softening; [[pretzel]]s and German [[lye roll]]s are glazed with a sodium hydroxide solution before baking to make them crisp. Owing to the difficulty in obtaining food grade sodium hydroxide in small quantities for home use, [[sodium carbonate]] is often used in place of sodium hydroxide.<ref name="Hominy">{{cite web| url=http://www.uga.edu/nchfp/publications/uga/hominy_without_lye.html| title=Hominy without Lye| publisher=National Center for Home Food Preservation| access-date=2019-01-15| archive-date=2011-09-11| archive-url=https://web.archive.org/web/20110911000538/http://www.uga.edu/nchfp/publications/uga/hominy_without_lye.html| url-status=dead}}</ref> It is known as [[E number]] E524.

Specific foods processed with sodium hydroxide include:

* German [[pretzel]]s are poached in a boiling [[sodium carbonate]] solution or cold sodium hydroxide solution before baking, which contributes to their unique crust.

* Lye water is an essential ingredient in the crust of the traditional baked Chinese moon cakes.

* Most yellow coloured [[Chinese noodles]] are made with lye water but are commonly mistaken for containing egg.

* One variety of [[zongzi]] uses lye water to impart a sweet flavor.

* Sodium hydroxide causes gelling of egg whites in the production of [[century egg]]s.

* Some methods of preparing olives involve subjecting them to a lye-based brine.<ref>{{cite web |url=http://ucanr.org/freepubs/docs/8267.pdf |title=Olives: Safe Methods for Home Pickling (application/pdf Object) |work=ucanr.org |year=2010 |access-date=January 22, 2012 |archive-date=January 17, 2012 |archive-url=https://web.archive.org/web/20120117053826/http://ucanr.org/freepubs/docs/8267.pdf |url-status=dead }}</ref>

* The Filipino dessert ({{lang-fil|kakanin}}) called {{lang|fil|[[kutsinta]]}} uses a small quantity of lye water to help give the rice flour batter a jelly-like consistency. A similar process is also used in the kakanin known as {{lang|fil|[[pitsi-pitsi]]}} or {{lang|fil|pichi-pichi}} except that the mixture uses grated [[cassava]] instead of rice flour.

* The [[Norway|Norwegian]] dish known as [[lutefisk]] ({{lang-no|lutfisk|lit=lye fish}}).

* [[Bagel]]s are often boiled in a lye solution before baking, contributing to their shiny crust.

* [[Hominy]] is dried [[maize]] (corn) kernels reconstituted by soaking in lye-water. These expand considerably in size and may be further processed by frying to make [[corn nuts]] or by drying and grinding to make [[grits]]. Hominy is used to create [[masa]], a popular flour used in Mexican cuisine to make [[corn tortillas]] and [[tamales]]. [[Nixtamal]] is similar, but uses [[calcium hydroxide]] instead of sodium hydroxide.

===Cleaning agent===

{{Main|Cleaning agent}}

Sodium hydroxide is frequently used as an industrial [[cleaning agent]] where it is often called "caustic". It is added to water, heated, and then used to clean process equipment, storage tanks, etc. It can dissolve [[grease (lubricant)|grease]], [[oils]], [[fat]]s and [[protein]]-based deposits. It is also used for cleaning waste discharge pipes under sinks and drains in domestic properties. [[Surfactants]] can be added to the sodium hydroxide solution in order to stabilize dissolved substances and thus prevent redeposition. A sodium hydroxide soak solution is used as a powerful degreaser on [[stainless steel]] and glass bakeware. It is also a common ingredient in oven cleaners.

A common use of sodium hydroxide is in the production of [[parts washer]] [[detergent]]s. Parts washer detergents based on sodium hydroxide are some of the most aggressive parts washer cleaning chemicals. The sodium hydroxide-based detergents include surfactants, rust inhibitors and defoamers. A parts washer heats water and the detergent in a closed cabinet and then sprays the heated sodium hydroxide and hot water at pressure against dirty parts for degreasing applications. Sodium hydroxide used in this manner replaced many solvent-based systems in the early 1990s{{Citation needed|date=May 2010}} when [[1,1,1-Trichloroethane|trichloroethane]] was outlawed by the [[Montreal Protocol]]. Water and sodium hydroxide detergent-based parts washers are considered to be an environmental improvement over the solvent-based cleaning methods.

[[File:NaOH - drain-cleaner.jpg|thumb|left|upright|[[Hardware store]]s grade sodium hydroxide to be used as a type of [[Chemical drain cleaners#Alkaline drain openers|drain cleaner]].]]

[[File:Paint stripping with caustic soda.jpg|thumb|upright|Paint stripping with caustic soda]]

Sodium hydroxide is used in the home as a type of [[chemical drain cleaners#Alkaline drain openers|drain openers]] to unblock clogged drains, usually in the form of a dry crystal or as a thick liquid gel. The alkali dissolves [[fat|greases]] to produce [[water soluble]] [[product (chemistry)|products]]. It also [[hydrolysis|hydrolyzes]] [[proteins]], such as those found in [[hair]], which may block water pipes. These reactions are sped by the [[exothermic|heat generated]] when sodium hydroxide and the other chemical components of the cleaner dissolve in water. Such [[chemical drain cleaners#Alkaline drain openers|alkaline drain cleaners]] and their [[chemical drain cleaners#Acidic drain openers|acidic versions]] are highly [[corrosive]] and should be handled with great caution.

=== Relaxer ===

Sodium hydroxide is used in some [[relaxer]]s to [[straighten hair]]. However, because of the high incidence and intensity of chemical burns, manufacturers of chemical relaxers use other alkaline chemicals in preparations available to consumers. Sodium hydroxide relaxers are still available, but they are used mostly by professionals.

=== Paint stripper ===

A solution of sodium hydroxide in water was traditionally used as the most common paint stripper on wooden objects. Its use has become less common, because it can damage the wood surface, raising the grain and staining the colour.

===Water treatment===

Sodium hydroxide is sometimes used during [[water purification]] to raise the pH of water supplies. Increased pH makes the water less corrosive to plumbing and reduces the amount of lead, copper and other toxic metals that can dissolve into drinking water.<ref>{{cite web|url=http://articles.extension.org/pages/32302/drinking-water-treatment-ph-adjustment|title=Drinking Water Treatment – pH Adjustment|year=2011|access-date=June 23, 2016|archive-date=August 10, 2018|archive-url=https://web.archive.org/web/20180810194639/http://articles.extension.org/pages/32302/drinking-water-treatment-ph-adjustment|url-status=dead}}</ref><ref>{{cite web|url=http://www.water-research.net/index.php/drinking-water-issues-corrosive-water-lead-copper-aluminum-zinc-and-more|author=Brian Oram, PG|title=Drinking Water Issues Corrosive Water (Lead, Copper, Aluminum, Zinc and More)|year=2014|access-date=June 23, 2016|archive-date=July 1, 2016|archive-url=https://web.archive.org/web/20160701214918/http://www.water-research.net/index.php/drinking-water-issues-corrosive-water-lead-copper-aluminum-zinc-and-more|url-status=dead}}</ref>

===Historical uses===

Sodium hydroxide has been used for detection of [[carbon monoxide poisoning]], with blood samples of such patients turning to a [[vermilion]] color upon the addition of a few drops of sodium hydroxide.<ref>[https://books.google.com/books?id=2df7-uOC8ZwC&pg=PA168 Page 168] in: ''The Detection of poisons and strong drugs''.

Author: Wilhelm Autenrieth.

Publisher: P. Blakiston's son & Company, 1909.</ref> Today, carbon monoxide poisoning can be detected by [[CO oximetry]].

=== In cement mixes, mortars, concrete, grouts ===

Sodium hydroxide is used in some cement mix plasticisers. This helps homogenise cement mixes, preventing segregation of sands and cement, decreases the amount of water required in a mix and increases workability of the cement product, be it mortar, render or concrete.

==Safety==

[[File:Sodium hydroxide burn.png|thumb|right|[[Chemical burn]]s caused by sodium hydroxide solution photographed 44 hours after exposure.]]

Like other [[corrosive]] [[acid]]s and [[alkali]]s, a few drops of sodium hydroxide solutions can readily decompose [[proteins]] and [[lipids]] in [[Tissue (biology)|living tissues]] via [[amide hydrolysis]] and [[ester hydrolysis]], which consequently cause [[chemical burn]]s and may induce permanent [[blindness]] upon contact with eyes.<ref name="msd" /><ref name="msd2" /> Solid alkali can also express its corrosive nature if there is water, such as water vapor. Thus, [[protective equipment]], like [[rubber gloves]], [[safety clothing]] and [[eye protection]], should always be used when handling this chemical or its solutions. The standard first aid measures for alkali spills on the skin is, as for other corrosives, irrigation with large quantities of water. Washing is continued for at least ten to fifteen minutes.

Moreover, [[solvation|dissolution]] of sodium hydroxide is highly [[exothermic]], and the resulting heat may cause heat burns or ignite flammables. It also produces heat when reacted with acids.

Sodium hydroxide is mildly corrosive to [[glass]], which can cause damage to [[glazing (window)|glazing]] or cause [[ground glass joint]]s to bind.<ref>{{cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/sodium_hydroxide|title=SODIUM HYDROXIDE {{!}} NaOH – PubChem|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|access-date=2016-09-04}}</ref> Sodium hydroxide is corrosive to several metals, like [[aluminium]] which reacts with the alkali to produce flammable [[hydrogen]] gas on contact.<ref>{{cite web |url=http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/aluminium_water_hydrogen.pdf |title=aluminium_water_hydrogen.pdf (application/pdf Object) |work=www1.eere.energy.gov |year=2008 |access-date=January 15, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20120914043825/http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/aluminium_water_hydrogen.pdf |archive-date=September 14, 2012 }}</ref>

== Storage ==

[[File:NaOH beads.jpg|thumb|Two industrial fiberglass barrels of caustic-soda]]Careful storage is needed when handling sodium hydroxide for use, especially bulk volumes. Following proper NaOH storage guidelines and maintaining worker/environment safety is always recommended given the chemical's burn hazard.

Sodium hydroxide is often stored in bottles for small-scale laboratory use, within [[intermediate bulk container]]s (medium volume containers) for cargo handling and transport, or within large stationary storage tanks with volumes up to 100,000 gallons for manufacturing or waste water plants with extensive NaOH use. Common materials that are compatible with sodium hydroxide and often utilized for NaOH storage include: polyethylene ([[HDPE]], usual, [[Cross-linked polyethylene|XLPE]], less common), [[carbon steel]], [[polyvinyl chloride]] (PVC), [[stainless steel]], and [[fiberglass reinforced plastic]] (FRP, with a resistant liner).<ref name="Protank-2018" />

Sodium hydroxide must be stored in airtight containers to preserve its [[Equivalent concentration|normality]] as it will absorb water and carbon dioxide from the atmosphere.

== History ==

Sodium hydroxide was first prepared by soap makers.<ref name="thorpe">Thorpe, Thomas Edward, ed., ''A Dictionary of Applied Chemistry'' (London, England: Longmans, Green, and Co., 1913), vol. 5, [https://books.google.com/books?id=7tI5AQAAIAAJ&pg=PA36]</ref>{{rp|p45}} A procedure for making sodium hydroxide appeared as part of a recipe for making soap in an Arab book of the late 13th century: {{Transliteration|ar|Al-mukhtara' fi funun min al-suna'}} (Inventions from the Various Industrial Arts), which was compiled by al-Muzaffar Yusuf ibn 'Umar ibn 'Ali ibn Rasul (d. 1295), a king of Yemen.<ref>See: [http://www.history-science-technology.com/notes/notes5.html History of Science and Technology in Islam: Description of Soap Making]</ref><ref>The English chemist and archaeologist [[Henry Ernest Stapleton]] (1878–1962) presented evidence that the Persian alchemist and physician [[Muhammad ibn Zakariya al-Razi]] (c. 865–925) knew about sodium hydroxide. See {{cite journal<!--Citation bot bypass-->|last1=Stapleton|first1=Henry E.|author1-link=Henry Ernest Stapleton|last2=Azo|first2=R.F.|last3=Hidayat Husain|first3=M.|year=1927|title=Chemistry in Iraq and Persia in the Tenth Century A.D.|journal=Memoirs of the Asiatic Society of Bengal|volume=VIII|issue=6|pages=317–418|oclc=706947607|url=http://www.southasiaarchive.com/Content/sarf.100203/231270}} p. 322.</ref> The recipe called for passing water repeatedly through a mixture of ''[[alkali]]'' (Arabic: {{Transliteration|ar|al-qily}}, where {{Transliteration|ar|qily}} is ash from [[Glasswort|saltwort]] plants, which are rich in sodium; hence ''alkali'' was impure [[sodium carbonate]])<ref>{{cite journal|last1=Stapleton|first1=Henry E.|author1-link=Henry Ernest Stapleton|last2=Azo|first2=R.F.|date=1905|title=Alchemical equipment in the eleventh century, A.D.|journal=Memoirs of the Asiatic Society of Bengal|volume=I|issue=4|pages=47–71|url=https://archive.org/details/in.ernet.dli.2015.228305/page/n73/mode/2up}} See [https://archive.org/details/in.ernet.dli.2015.228305/page/n79/mode/2up footnote 5 on p. 53.] From p. 53: "5. Sodium carbonate. Qily is the ashes of certain plants, e.g. Salsola and Salicornia … , which grow near the sea, or in salty places … "</ref> and quicklime ([[calcium oxide]], CaO), whereby a solution of sodium hydroxide was obtained. European soap makers also followed this recipe. When in 1791 the French chemist and surgeon [[Nicolas Leblanc]] (1742–1806) patented a [[Leblanc process|process for mass-producing sodium carbonate]], natural "soda ash" (impure sodium carbonate that was obtained from the ashes of plants that are rich in sodium)<ref name="thorpe" />{{rp|p36}} was replaced by this artificial version.<ref name="thorpe" />{{rp|p46}} However, by the 20th century, the [[Chloralkali process|electrolysis of sodium chloride]] had become the primary method for producing sodium hydroxide.<ref>O'Brien, Thomas F.; Bommaraju, Tilak V. and Hine, Fumio (2005) ''Handbook of Chlor-Alkali Technology'', vol. 1. Berlin, Germany: Springer. Chapter 2: History of the Chlor-Alkali Industry, p. 34. {{ISBN|9780306486241}}</ref>

==See also==

* [[pH|Acid and base]]

* [[HAZMAT Class 8 Corrosive Substances]]

* [[List of cleaning agents]]

==References==

{{Reflist|30em}}

==Bibliography==

* {{cite book | editor= Haynes, William M. | year = 2011 | title = CRC Handbook of Chemistry and Physics | edition = 92nd | publisher = [[CRC Press]] | isbn = 978-1439855119| title-link = CRC Handbook of Chemistry and Physics }}

==External links==

{{Commons category}}

{{Wiktionary}}

* [http://www.inchem.org/documents/icsc/icsc/eics0360.htm International Chemical Safety Card 0360]

* Euro Chlor-How is chlorine made? [https://web.archive.org/web/20060923075635/http://www.eurochlor.org/makingchlorine Chlorine Online]

* [https://www.cdc.gov/niosh/npg/npgd0565.html NIOSH Pocket Guide to Chemical Hazards]

* [https://www.cdc.gov/niosh/topics/sodium-hydroxide/ CDC – Sodium Hydroxide – NIOSH Workplace Safety and Health Topic]

* [https://web.archive.org/web/20090518141937/http://electrochem.cwru.edu/encycl/art-b01-brine.htm Production by brine electrolysis]

* Data sheets

** [https://www.oxy.com/globalassets/documents/chemicals/products/chlor-alkali/caustic.pdf Technical charts (page 33—41)] for enthalpy, temperature and pressure

** [https://web.archive.org/web/20160404052444/http://www.sciencelab.com/msds.php?msdsId=9924999 Sodium Hydroxide MSDS]

** [http://www.certified-lye.com/MSDS-Lye.pdf Certified Lye MSDS] {{Webarchive|url=https://web.archive.org/web/20080228005947/http://www.certified-lye.com/MSDS-Lye.pdf |date=2008-02-28 }}

** [https://web.archive.org/web/20120803005424/http://www.hillbrothers.com/msds/pdf/sodium-hydroxide-10-50-liq.pdf Hill Brothers MSDS]

* [http://www2.iq.usp.br/docente/gutz/Curtipot_.html Titration of acids with sodium hydroxide; freeware for data analysis, simulation of curves and pH calculation]

* [https://web.archive.org/web/20150508191719/http://www.inclusive-science-engineering.com/inorganic-chemical-caustic-soda-production-process-description-and-flowsheet/ Caustic soda production in continuous causticising plant by lime soda process]

{{Sodium compounds}}

{{Hydroxides}}

{{Molecules detected in outer space}}

{{Electrolysis}}

{{Authority control}}

{{DEFAULTSORT:Sodium Hydroxide}}

[[Category:Chemical engineering]]

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[[Category:Deliquescent materials]]

[[Category:Desiccants]]

[[Category:Household chemicals]]

[[Category:Hydroxides]]

[[Category:Inorganic compounds]]

[[Category:Photographic chemicals]]

[[Category:Sodium compounds]]

[[Category:E-number additives]]

[[Category:Food acidity regulators]]