Sodium hydroxide is a highlycorrosivebase andalkali that decomposeslipids andproteins at ambienttemperatures and may cause severechemical burns. It is highly soluble inwater, and readily absorbsmoisture andcarbon dioxide from theair. It forms a series ofhydratesNaOH·nH2O.[13] The monohydrateNaOH·H2O crystallizes from water solutions between 12.3 and 61.8 °C. The commercially available "sodium hydroxide" is often this monohydrate, and published data may refer to it instead of theanhydrous compound.
As one of the simplest hydroxides, sodium hydroxide is frequently used alongside neutralwater and acidichydrochloric acid to demonstrate the pH scale to chemistry students.[14]
Pure sodium hydroxide is a colorless crystalline solid that melts at 318 °C (604 °F) without decomposition and boils at 1,388 °C (2,530 °F). It is highly soluble in water, with a lower solubility inpolarsolvents such asethanol andmethanol.[16] Sodium hydroxide is insoluble inether and other non-polar solvents.
Similar to the hydration of sulfuric acid,dissolution of solid sodium hydroxide in water is a highlyexothermic reaction[17] 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 ofsaponification that occurs betweenNaOH and natural skin oils.
Concentrated (50%) aqueous solutions of sodium hydroxide have a characteristicviscosity, 78 mPa·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 aqueousNaOH, 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.[16]
Sodium hydroxide can form several hydratesNaOH·nH2O, which result in a complex solubility diagram that was described in detail bySpencer Umfreville Pickering in 1893.[18] The known hydrates and the approximate ranges of temperature and concentration (mass percent of NaOH) of theirsaturated water solutions are:[13]
Heptahydrate,NaOH·7H2O: from −28 °C (18.8%) to −24 °C (22.2%).[18]
Pentahydrate,NaOH·5H2O: from −24 °C (22.2%) to −17.7 °C (24.8%).[18]
Tetrahydrate,NaOH·4H2O, α form: from −17.7 °C (24.8%) to 5.4 °C (32.5%).[18][19]
Dihydrate,NaOH·2H2O: from 5.0 °C (45.7%) to 12.3 °C (51%).[18][13]
Monohydrate,NaOH·H2O: from 12.3 °C (51%) to 65.10 °C (69%) then to 62.63 °C (73.1%).[18][20]
Early reports refer to hydrates withn = 0.5 orn = 2/3, but later careful investigations failed to confirm their existence.[20]
The only hydrates with stable melting points areNaOH·H2O (65.10 °C) andNaOH·3.5H2O (15.38 °C). The other hydrates, except the metastable onesNaOH·3H2O andNaOH·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.[13][20]
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 °C) before the dihydrate. However, the solution can easily be supercooled down to −15 °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 °C; however, once the temperature exceeds 12.58 °C it often decomposes into solid monohydrate and a liquid solution. Even then = 3.5 hydrate is difficult to crystallize, because the solution supercools so much that other hydrates become more stable.[13]
A hot water solution containing 73.1% (mass) of NaOH is aeutectic that solidifies at about 62.63 °C as an intimate mix of anhydrous and monohydrate crystals.[21][20]
A second stable eutectic composition is 45.4% (mass) of NaOH, that solidifies at about 4.9 °C into a mixture of crystals of the dihydrate and of the 3.5-hydrate.[13]
The third stable eutectic has 18.4% (mass) of NaOH. It solidifies at about −28.7 °C as a mixture of water ice and the heptahydrateNaOH·7H2O.[18][22]
When solutions with less than 18.4% NaOH are cooled, waterice crystallizes first, leaving the NaOH in solution.[18]
The α form of the tetrahydrate has density 1.33 g/cm3. It melts congruously at 7.55 °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 °C it may instead melt incongruously into a mixture of solidNaOH·3.5H2O and a liquid solution.[19]
The β form of the tetrahydrate is metastable, and often transforms spontaneously to the α form when cooled below −20 °C.[19] 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 °C, and melts partially at −1.83 °C.[19]
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.
NaOH and its monohydrate form orthorhombic crystals with the space groups Cmcm (oS8) and Pbca (oP24), respectively. The monohydrate cell dimensions are a = 1.1825, b = 0.6213, c = 0.6069nm. The atoms are arranged in ahydrargillite-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 byhydrogen bonds between water molecules.[23]
Sodium hydroxide reacts with protic acids to produce water and the corresponding salts. For example, when sodium hydroxide reacts withhydrochloric acid,sodium chloride is formed:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
In general, suchneutralization reactions are represented by one simple net ionic equation:
Sodium hydroxide also reacts withacidic oxides, such assulfur dioxide. Such reactions are often used to "scrub" harmful acidic gases (likeSO2 andH2S) produced in the burning of coal and thus prevent their release into the atmosphere. For example,
Glass reacts slowly with aqueous sodium hydroxide solutions at ambient temperatures to form solublesilicates. Because of this, glass joints andstopcocks exposed to sodium hydroxide have a tendency to "freeze".Flasks and glass-linedchemical reactors are damaged by long exposure to hot sodium hydroxide, which also frosts the glass. Sodium hydroxide does not attackiron at room temperature, since iron does not haveamphoteric properties (i.e., it only dissolves in acid, not base).Nevertheless, at high temperatures (e.g. above 500 °C), iron can reactendothermically with sodium hydroxide to formiron(III) oxide,sodium metal, andhydrogen gas.[24] This is due to the lowerenthalpy 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 (ΔST > ΔH,ΔG < 0) and non-spontaneity at low temperatures (ΔST < ΔH,ΔG > 0). Consider the following reaction between molten sodium hydroxide and finely divided iron filings:
4 Fe + 6 NaOH → 2 Fe2O3 + 6 Na + 3 H2
A fewtransition metals, however, may react quite vigorously with sodium hydroxide under milder conditions.
In 1986, an aluminiumroad tanker in the UK was mistakenly used to transport 25% sodium hydroxide solution,[25] 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:
Unlike sodium hydroxide, which is soluble, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used toprecipitate 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 ofNa2ZnO2 orNa2PbO2.
Sodium hydroxide can be used for the base-drivenhydrolysis of esters (also calledsaponification),amides andalkyl halides.[16] However, the limited solubility of sodium hydroxide in organic solvents means that the moresolublepotassium 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 assebum are converted to soap.Despite solubility inpropylene 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.
Sodium hydroxide is industrially produced, first as a 32% solution, and then evaporated to a 50% solution by variations of the electrolyticchloralkali process.[26]Chlorine gas is the main product from this process.[27][26] Solid sodium hydroxide is obtained from this solution by the evaporation of water. Solid sodium hydroxide is most commonly sold as flakes,prills, and cast blocks.[28]
Historically, sodium hydroxide was produced by treatingsodium carbonate withcalcium hydroxide (slaked lime) in ametathesis reaction which takes advantage of the fact that sodium hydroxide is soluble, while calcium carbonate is not. This process was called causticizing.[30]
Ca(OH)2(aq) + Na2CO3(s) → CaCO3(s) + 2 NaOH(aq)
The sodium carbonate for this reaction was produced by theLeblanc process in the early 19th century, or theSolvay process in the late 19th century. The conversion of sodium carbonate to sodium hydroxide was superseded entirely by thechloralkali 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.
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 themercury cell chloralkali process wheresodium amalgam is reacted with water.
Sodium hydroxide is a popular strongbase 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 anaqueous solution,[31] since solutions are cheaper and easier to handle.
Sodium hydroxide is used in many scenarios where it is desirable to increase thealkalinity of a mixture, or to neutralize acids. For example, in the petroleum industry, sodium hydroxide is used as an additive indrilling mud to increasealkalinity inbentonite mud systems, to increase the mudviscosity, and to neutralize anyacid gas (such ashydrogen sulfide andcarbon dioxide) which may be encountered in thegeological formation as drilling progresses. Another use is insalt spray testing 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 qualitycrude oil can be treated with sodium hydroxide to removesulfurous impurities in a process known ascaustic washing. Sodium hydroxide reacts with weak acids such ashydrogen sulfide andmercaptans 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 thendumped the waste in Ivory Coast.[32][33]
Other common uses of sodium hydroxide include:
for making soaps and detergents. Sodium hydroxide is used for hard bar soap, whilepotassium hydroxide is used for liquid soaps.[34][35] Sodium hydroxide is used more often thanpotassium 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
Sodium hydroxide is also widely used in pulping of wood for making paper or regenerated fibers. Along withsodium sulfide, sodium hydroxide is a key component of the white liquor solution used to separatelignin fromcellulosefibers in thekraft process. It also plays a key role in several later stages of the process ofbleaching the brown pulp resulting from the pulping process. These stages includeoxygen delignification,oxidative extraction, and simple extraction, all of which require a strong alkaline environment with a pH > 10.5 at the end of the stages.
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,[36][37] and the only solids that remain are bone hulls, which can be crushed between one's fingertips.[38]
Sodium hydroxide is frequently used in the process of decomposingroadkill dumped in landfills by animal disposal contractors.[37] Due to its availability and low cost, it has been used by criminals to dispose of corpses. Italianserial killerLeonarda Cianciulli used this chemical to turn dead bodies into soap.[39] In Mexico, a man who worked for drug cartels admitted disposing of over 300 bodies with it.[40]
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.[41]
Strong bases attackaluminium. 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 produceshydrogen gas andsodium aluminate. In this reaction, sodium hydroxide acts as an agent to make the solution alkaline, which aluminium can dissolve in.
2 Al + 2NaOH + 2 H2O → 2NaAlO2 +3 H2
Sodium aluminate is an inorganic chemical that is used as an effective source ofaluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given asNaAlO2,Na3AlO3,Na[Al(OH)4],Na2O·Al2O3 orNa2Al2O4. Formation of sodium tetrahydroxoaluminate(III) or hydrated sodium aluminate is given by:[42]
2 Al + 2 NaOH + 6 H2O→ 2 Na[Al(OH)4] + 3 H2
This reaction can be useful inetching, removing anodizing, or converting a polished surface to a satin-like finish, but without furtherpassivation such asanodizing oralodining the surface may become degraded, either under normal use or in severe atmospheric conditions.
In theBayer 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 theelectrolyticHall-Héroult process. Since the alumina isamphoteric, it dissolves in the sodium hydroxide, leaving impurities less soluble at highpH such asiron oxides behind in the form of a highly alkalinered mud.
Other amphoteric metals are zinc and lead which dissolve in concentrated sodium hydroxide solutions to givesodium zincate andsodium plumbate respectively.
Sodium hydroxide is traditionally used in soap making (cold process soap,saponification).[43] 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 ofbiodiesel, sodium hydroxide is used as acatalyst for thetransesterification of methanol and triglycerides. This only works withanhydrous sodium hydroxide, because combined with water the fat would turn intosoap, which would be tainted withmethanol. NaOH is used more often thanpotassium 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.[44]
Sodium hydroxide is an ingredient used in someskin care andcosmetic products, such as facial cleansers, creams, lotions, and makeup. It is typically used in low concentration as apH balancer, due its highly alkaline nature.[45]
Food uses of sodium hydroxide include washing or chemical peeling offruits andvegetables,chocolate andcocoa processing,caramel coloring production,poultry scalding,soft drink processing, and thickeningice cream.[46]Olives are often soaked in sodium hydroxide for softening;pretzels and Germanlye rolls 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.[47] It is known asE number E524.
Specific foods processed with sodium hydroxide include:
Germanpretzels are poached in a boilingsodium 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 colouredChinese noodles are made with lye water but are commonly mistaken for containing egg.
One variety ofzongzi uses lye water to impart a sweet flavor.
Sodium hydroxide causes gelling of egg whites in the production ofcentury eggs.
Some methods of preparing olives involve subjecting them to a lye-based brine.[48]
The Filipino dessert (Filipino:kakanin) calledkutsinta 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 aspitsi-pitsi orpichi-pichi except that the mixture uses gratedcassava instead of rice flour.
Bagels are often boiled in a lye solution before baking, contributing to their shiny crust.
Hominy is driedmaize (corn) kernels reconstituted by soaking in lye-water. These expand considerably in size and may be further processed by frying to makecorn nuts or by drying and grinding to makegrits. Hominy is used to createmasa, a popular flour used in Mexican cuisine to makecorn tortillas andtamales.Nixtamal is similar, but usescalcium hydroxide instead of sodium hydroxide.
Sodium hydroxide is frequently used as an industrialcleaning 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 dissolvegrease,oils,fats andprotein-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 onstainless steel and glass bakeware. It is also a common ingredient in oven cleaners.
A common use of sodium hydroxide is in the production ofparts washerdetergents. 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] whentrichloroethane was outlawed by theMontreal Protocol. Water and sodium hydroxide detergent-based parts washers are considered to be an environmental improvement over the solvent-based cleaning methods.
Sodium hydroxide is used in the home as a type ofdrain openers to unblock clogged drains, usually in the form of a dry crystal or as a thick liquid gel. The alkali reacts withgreases to producewater soluble soap andglycerol. It alsohydrolyzesproteins, such as those found inhair, which may block waste water pipes. Dissolving sodium hydroxide in water is anexothermic reaction producing considerable quantities of heat which assists in speeding up the reactions with grease and other organic matter. Suchalkaline drain cleaners and theiracidic versions are highlycorrosive and should be handled with great caution.
Sodium hydroxide is used in somerelaxers tostraighten 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.
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.
Sodium hydroxide is sometimes used duringwater 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.[49][50]
Sodium hydroxide has been used for detection ofcarbon monoxide poisoning, with blood samples of such patients turning to avermilion color upon the addition of a few drops of sodium hydroxide.[51] Today, carbon monoxide poisoning can be detected byCO oximetry.
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.
Chemical burns caused by sodium hydroxide solution photographed 44 hours after exposure.
Like othercorrosiveacids andalkalis, a few drops of sodium hydroxide solutions can readily decomposeproteins andlipids inliving tissues viaamide hydrolysis andester hydrolysis, which consequently causechemical burns and may induce permanentblindness upon contact with eyes.[1][2] Solid alkali can also express its corrosive nature if there is water, such as water vapor. Thus,protective equipment, likerubber gloves,safety clothing andeye 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,dissolution of sodium hydroxide is highlyexothermic, and the resulting heat may cause heat burns or ignite flammables. It also produces heat when reacted with acids.
Sodium hydroxide is mildly corrosive toglass, which can cause damage toglazing or causeground glass joints to bind.[52] Sodium hydroxide is corrosive to several metals, likealuminium which reacts with the alkali to produce flammablehydrogen gas on contact.[53]
Sodium hydroxide's toxicity level for fish etc. is around 20—200 mg/l and associated with increased pH value. However as it is quickly neutralised and does not accumulate, its effect on the environment is usually easily handled.[54]
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, withinintermediate bulk containers (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,XLPE, less common),carbon steel,polyvinyl chloride (PVC),stainless steel, andfiberglass reinforced plastic (FRP, with a resistant liner).[16]
Sodium hydroxide must be stored in airtight containers to preserve itsnormality as it will absorb water and carbon dioxide from the atmosphere.
Sodium hydroxide was first prepared by soap makers.[55]: 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: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 ofYemen.[56][57]
The recipe called for passing water repeatedly through a mixture ofalkali (Arabic:al-qily, whereqily is ash fromsaltwort plants, which are rich in sodium; hencealkali was impuresodium carbonate)[58] 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 surgeonNicolas Leblanc (1742–1806) patented aprocess for mass-producing sodium carbonate, natural "soda ash" (impure sodium carbonate that was obtained from the ashes of plants that are rich in sodium)[55]: p36 was replaced by this artificial version.[55]: p46 However, by the 20th century, theelectrolysis of sodium chloride had become the primary method for producing sodium hydroxide.[59]
^Jacobs, H.; Kockelkorn, J. and Tacke, Th. (1985). "Hydroxide des Natriums, Kaliums und Rubidiums: Einkristallzüchtung und röntgenographische Strukturbestimmung an der bei Raumtemperatur stabilen Modifikation".Z. Anorg. Allg. Chem.531 (12):119–124.doi:10.1002/zaac.19855311217.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^abcdefgSiemens, P. R.; Giauque, William F. (1969). "Entropies of the hydrates of sodium hydroxide. II. Low-temperature heat capacities and heats of fusion of NaOH·2H2O and NaOH·3.5H2O".Journal of Physical Chemistry.73 (1):149–157.doi:10.1021/j100721a024.
^abcdeMraw, S. C.; Giauque, W. F. (1974). "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".Journal of Physical Chemistry.78 (17):1701–1709.doi:10.1021/j100610a005.
^abcdMurch, L. E.; Giauque, W. F. (1962). "The thermodynamic properties of sodium hydroxide and its monohydrate. Heat capacities to low temperatures. Heats of solution".Journal of Physical Chemistry.66 (10):2052–2059.doi:10.1021/j100816a052.
^Brodale, G. E.; Giauque, W. F. (1962). "The freezing point-solubility curve of aqueous sodium hydroxide in the region near the anhydrous-monohydrate eutectic".Journal of Physical Chemistry.66 (10): 2051.doi:10.1021/j100816a051.
^Jacobs, H. and Metzner, U. (1991). "Ungewöhnliche H-Brückenbindungen in Natriumhydroxidmonohydrat: Röntgen- und Neutronenbeugung an NaOH·H<sub">2</sub">O bzw. NaOD·D<sub">2</sub">O".Zeitschrift für anorganische und allgemeine Chemie.597 (1):97–106.doi:10.1002/zaac.19915970113.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^abFengmin Du, David M Warsinger, Tamanna I Urmi, Gregory P Thiel, Amit Kumar, John H Lienhard (2018). "Sodium hydroxide production from seawater desalination brine: process design and energy efficiency".Environmental Science & Technology.52 (10):5949–5958.Bibcode:2018EnST...52.5949D.doi:10.1021/acs.est.8b01195.hdl:1721.1/123096.PMID29669210.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Deming, Horace G. (1925).General Chemistry: An Elementary Survey Emphasizing Industrial Applications of Fundamental Principles (2nd ed.). New York: John Wiley & Sons, Inc. p. 452.
^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.ISBN9780306486241
