Sodium hydroxide
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2008-07-16T00:26:01Z
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{{Mergefrom|Manufacture of Sodium hydroxide by Nelson's process|date=January 2008}}
{{Chembox new
| Name = Sodium hydroxide
| ImageFile = Sodium hydroxide.jpg
| ImageFile1 = Sodium-hydroxide-crystal-3D-vdW.png
| IUPACName = Sodium hydroxide
| OtherNames = Lye, Caustic Soda
| Section1 = {{Chembox Identifiers
| CASNo = 1310-73-2
}}
| Section2 = {{Chembox Properties
| Formula = NaOH
| MolarMass = 39.9971 g/mol
| Appearance = White solid
| Density = 2.1 g/cm³, solid
| Solubility = 111 g/100 ml (20°C)
| MeltingPt = 318°C (591 K)
| BoilingPt = 1390°C (1663 K)
| pKb = -2.43
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://physchem.ox.ac.uk/MSDS/SO/sodium_hydroxide.html External MSDS]
| NFPA-H = 3
| NFPA-F =
| NFPA-R = 1
| FlashPt = Non-flammable.
}}
| Section8 = {{Chembox Related
| Function = [[alkali hydroxide]]s
| OtherFunctn = [[Lithium hydroxide]] <br />[[Potassium hydroxide]] <br />[[Rubidium hydroxide]] <br />[[Caesium hydroxide]]
}}
}}
'''Sodium hydroxide''' ([[sodium|Na]][[hydroxide|OH]]), also known as '''[[lye]]''', '''caustic soda''' and (incorrectly, according to [[IUPAC]] nomenclature)<ref>[http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf IUPAC RED Book, definition of "hydrate" salt, pp. 80–81]</ref> as '''sodium hydrate''', is a [[caustic (substance)|caustic]] metallic [[Base (chemistry)|base]]. Sodium hydroxide forms a strong [[alkaline]] solution when dissolved in a solvent such as water. It is used in many industries, mostly as a strong [[chemical compound|chemical]] [[pH|base]] in the manufacture of [[wood pulp|pulp]] and [[paper]], [[textile]]s, [[drinking water]], [[soap]]s and [[detergent]]s and as a [[drain cleaner]]. Worldwide production in 1998 was around 45 million [[tonne]]s. Sodium hydroxide is the most used base in chemical laboratories.
Pure sodium hydroxide is a white solid; available in pellets, flakes, granules and as a 50% saturated solution. It is [[deliquescent]] and readily absorbs [[carbon dioxide]] from the air, so it should be stored in an [[Hermetically sealed|airtight]] container. It is very soluble in water with liberation of heat. It also dissolves in [[ethanol]] and [[methanol]], though it exhibits lower solubility in these solvents than [[potassium hydroxide]]. It is insoluble in [[diethyl ether|ether]] and other non-polar solvents. A sodium hydroxide [[solution]] will leave a yellow stain on fabric and paper.
==Physical properties==
Δ H° dissolution for diluted aqueous -44.45 kJ / mol;
From aqueous solutions at 12.3-61.8°C, it crystallizes in monohydrate, with a melting point 65.1 °C and density of 1.829 g/cm 3;
Δ H° form -734.96 kJ / mol;
Monohydrate from -28 to -24°C;
Heptahydrate from -24 to -17.7°C;
Pentahydrate from -17.7 to -5.4°C;
Tetrahydrate (α- changed), at -5 , 4 - 12.3°C Also know metastable β- NaOH 4* H<sub>2</sub>O. Which above 61.8°C are crystallized.
==Chemical properties==
Sodium hydroxide is completely [[Ionic bonding|ionic]], containing sodium ions and [[hydroxide]] ions. The hydroxide ion makes sodium hydroxide a strong base which reacts with acids to form [[water]] and the corresponding salts, e.g., with [[hydrochloric acid]], [[sodium chloride]] is formed:
:NaOH([[Aqueous|aq]]) + [[Hydrochloric acid|HCl]](aq) → [[Sodium chloride|NaCl]](aq) + [[Water (molecule)|H<sub>2</sub>O]]([[Liquid|l]])
In general such [[neutralization (chemistry)|neutralization]] reactions are represented by one simple net ionic equation:
:[[Hydroxide|OH<sup>−</sup>]](aq) + [[Hydronium|H<sub>3</sub>O<sup>+</sup>(aq)]] → 2H<sub>2</sub>O
This type of reaction with a strong acid, releases heat, and hence is referred to as [[exothermic reaction|exothermic]]. Such [[acid-base reaction]]s can also be used for [[titration]]s, which is a common method to determine the concentration of acids.
Another type of reaction that sodium hydroxide is involved in is with acidic oxides. The reaction of [[carbon dioxide]] has already been mentioned, but other acidic oxides such as [[sulfur dioxide]] (SO<sub>2</sub>) also react completely. Such reactions are often used to "scrub" harmful acidic gases (like SO<sub>2</sub> and H<sub>2</sub>S) and prevent their release into the atmosphere.
:2NaOH + [[Carbon dioxide|CO<sub>2</sub>]] → [[Sodium carbonate|Na<sub>2</sub>CO<sub>3</sub>]] + H<sub>2</sub>O
Sodium hydroxide slowly reacts with glass to form [[sodium silicate]], so glass joints and [[stopcock]]s exposed to NaOH have a tendency to "freeze". [[Laboratory flask|Flask]]s and glass-lined [[chemical reactor]]s are damaged by long exposure to hot sodium hydroxide, and the glass becomes frosted. Sodium hydroxide does not attack [[iron]] since Iron does not have amphoteric properties. A few transition metals, however, may react with Sodium Hydroxide in a vigorous way.
In 1986 an aluminium [[tank truck|road tanker]] in the UK was mistakenly used to transport 25% sodium hydroxide solution, causing pressurization of the contents and damage to the tanker. The pressurization was due to the hydrogen gas which is produced in the reaction between sodium hydroxide and aluminium:
2Al<sub>(s)</sub> + 6NaOH<sub>(aq)</sub> → 3H<sub>2(g)</sub> + 2Na<sub>3</sub>AlO<sub>3(aq)</sub>
Unlike NaOH, the hydroxides of most metals are insoluble, and therefore sodium hydroxide can be used to precipitate metal hydroxides. One such hydroxide is [[aluminium hydroxide]], used as a gelatinous [[flocculation|floc]] to filter out particulate matter in [[water treatment]]. Aluminium hydroxide is prepared at the treatment plant from [[aluminium sulfate]] by reacting with NaOH. This reaction is highly profitable, and is hence an important synthesis reaction.
Sodium hydroxide reacts readily with [[carboxylic acid]]s to form their salts and is even a strong enough base to form salts with [[phenol]]s. NaOH can be used for the base-driven [[hydrolysis]] of [[ester]]s (as in [[saponification]]), [[amide]]s and [[alkyl halide]]s. However, the limited solubility of NaOH in organic solvents means that the more [[soluble]] [[Potassium hydroxide|KOH]] is often preferred.
[[Image:Ester hydrolysis.png|frame|center|Basic hydrolysis of an ester]]
==Manufacture==
In 1998, total world production was around 45 million [[tonne]]s. North America and Asia collectively contributed around 14 million tonnes, while Europe produced around 10 million tonnes.
===Methods of production===<!-- This section is linked from [[Mercury (element)]] -->
Sodium hydroxide is produced (along with [[chlorine]] and [[hydrogen]]) via the [[chloralkali process]]. This involves the [[electrolysis]] of an aqueous solution of [[sodium chloride]]. The sodium hydroxide builds up at the [[cathode]], where water is reduced to hydrogen gas and [[hydroxide]] ion:
:2Na<sup>+</sup> + 2H<sub>2</sub>O + 2e<sup>−</sup> → H<sub>2</sub> + 2NaOH
To produce NaOH it is necessary to prevent reaction of the NaOH with the [[chlorine]]. This is typically done in one of three ways, of which the membrane cell process is economically the most viable.
* '''Mercury cell process''' (also called the [[Castner-Kellner process]]) – Sodium ions are reduced to [[Sodium|sodium metal]], which forms an [[amalgam]] with a [[mercury (element)|mercury]] [[cathode]]; this sodium is then reacted with water to produce NaOH. There have been concerns about mercury releases, although modern plants claim to be safe in this regard.<ref>{{cite web|url=http://www.eurochlor.org/animations/mercury-cell.asp| title=Chlorine Online Diagram of mercury cell process| publisher=Euro Chlor| accessdate=2006-09-15}}</ref>
* '''Diaphragm cell process''' – uses a steel cathode, and the reaction of NaOH with Cl<sub>2</sub> is prevented using a porous [[diaphragm seal|diaphragm]], often made of [[asbestos|asbestos fibers]]. In the diaphragm cell process the anode area is separated from the cathode area by a permeable diaphragm. The brine is introduced into the anode compartment and flows through the diaphragm into the cathode compartment. A diluted caustic brine leaves the cell. The sodium hydroxide must usually be concentrated to 50% and the salt removed. This is done using an evaporative process with about three tonnes of steam per tonne of sodium hydroxide. The salt separated from the caustic brine can be used to saturate diluted brine. The chlorine contains oxygen and is purified by liquefaction and evaporation.<ref>{{cite web|url=http://www.eurochlor.org/makingchlorine| title=Euro Chlor - How is chlorine made?| publisher=Euro Chlor| accessdate=2006-09-15}}</ref><ref>{{cite web|url=http://www.eurochlor.org/animations/diaphragm-cell.asp| title=Chlorine Online Diagram of diaphragm cell process| publisher=Euro Chlor| accessdate=2006-09-15}}</ref>
* '''Membrane cell process''' – similar to the diaphragm cell process, with a [[Nafion]] membrane to separate the cathode and anode reactions. Only sodium ions and a little water pass through the membrane. It produces a higher quality of NaOH. Of the three processes, the membrane cell process requires the lowest consumption of electric energy and the amount of steam needed for concentration of the caustic is relatively small (less than one tonne per tonne of sodium hydroxide).<ref>{{cite web|url=http://www.eurochlor.org/animations/membrane-cell.asp| title=Chlorine Online Diagram of membrane cell process| publisher=Euro Chlor| accessdate=2006-09-15}}</ref><ref>{{cite web|url=http://www.eurochlor.org/makingchlorine| title=Euro Chlor - How is chlorine made?| publisher=Euro Chlor| accessdate=2006-09-15}}</ref>
An older method for sodium hydroxide production was the [[Leblanc process]], which produced [[sodium carbonate]], followed by roasting to create [[carbon dioxide]] and [[sodium oxide]]. This method is still occasionally used. It helped establish sodium hydroxide as an important commodity chemical.
The LeBlanc process was superseded by the [[Solvay process]] in the late 19th century.
===Major producers===
{{Globalize/USA}}
In the United States, the major producer of sodium hydroxide is the [[Dow Chemical Company]], which has annual production around 3.7 million [[tonne]]s from sites at [[Freeport, Texas]], and [[Plaquemine, Louisiana]]. Other major US producers include [[Oxychem]], [[PPG Industries|PPG]], [[Olin Corporation|Olin]], Pioneer Companies, Inc. (PIONA), and [[Formosa Plastics Group|Formosa]]. All of these companies use the [[chloralkali process]]<ref>See ''Kirk-Othmer'' in general references</ref>.
==Uses==
===General applications===
Sodium hydroxide is the principal strong [[base (chemistry)|base]] used in the chemical industry. In bulk it is most often handled as an [[aqueous]] [[solution]], since solutions are cheaper and easier to handle. It is used to drive chemical reactions and also for the [[neutralization]] of acidic materials. It can be used also as a neutralizing agent in petroleum refining. It is sometimes used as a cleaner.
===Paint stripper===
A solution of sodium hydroxide in water was traditionally used as the most common paint stripper on wooden objects. Due to its caustic nature and the fact that it can damage the wood surface raising the grain and staining the color, its use has become less common.
===Gold pennies===
Sodium hydroxide has also been used in conjunction with [[zinc]] for creation of the famous "Gold pennies" experiment. When a [[penny]] is boiled in a solution of NaOH together with some granular zinc metal ([[Hot-dip galvanizing|galvanized nails]] are one source), the color of the penny will turn silver in about 45 seconds. The penny is then held in the flame of a burner for a few seconds and it turns golden brown . The reason this happens is that granular zinc dissolves in NaOH to form Zn(OH)<sub>4</sub><sup>2-</sup> (tetrahydroxozincate). This zincate ion becomes reduced to metallic zinc on the surface of a [[copper]] penny. Zinc and copper when heated in a flame form [[brass]].
===Alumina production - [[Bayer process]]===
Sodium hydroxide is used in the refining of [[alumina]] containing ore ([[bauxite]]) to produce alumina (aluminium oxide) which is the raw material used to produce [[aluminium]] metal via the [[smelting]] process.
===Use in chemical analysis===
In [[analytical chemistry]], sodium hydroxide solutions are often used to measure the [[concentration]] of acids by [[titration]]. Since NaOH is not a [[primary standard]], solutions must first be standardised by titration against a standard such as [[Potassium hydrogen phthalate|KHP]]. [[Burette]]s exposed to NaOH should be rinsed out immediately after use to prevent "freezing" of the stopcock. Sodium hydroxide was traditionally used to test for [[cation]]s in [[Qualitative inorganic analysis|Qualitative Inorganic Analysis]], as well as to provide alkaline media for some reactions that need it, such as the [[Biuret]] test.
===Soap production===
Sodium hydroxide was traditionally used in soap making ([[cold process]] soap, [[saponification]]). The [[Arab]]s began producing soap in this way in the 7th century, and the same basic process is used today.
===Paper making===
Sodium hydroxide was also widely used in making paper. Along with [[sodium sulfide]], NaOH 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.
===Biodiesel===
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]]. It is used more often than [[potassium hydroxide]] because it is cheaper and a smaller quantity is needed.
===Aluminium etching===
Strong bases attack [[aluminium]]. This can be useful in etching through a resist, removing anodizing, or converting a polished surface to a satin-like finish, but without further [[passivation]] such as [[anodizing]] or [[alodining]] the surface may become degraded, either under normal use or in severe atmospheric conditions.
===Food preparation===
Food uses of sodium hydroxide include washing or chemical peeling of [[fruits]] and [[vegetables]], [[chocolate]] and [[cocoa]] processing, [[caramel]] color production, [[poultry]] scalding, [[soft drink]] processing, and thickening [[ice cream]]. [[Olive]]s are often soaked in sodium hydroxide to soften them, while [[pretzel]]s and [[Germany|German]] [[lye roll]]s are glazed with a sodium hydroxide solution before baking to make them crisp. Due to the difficulty in obtaining food grade sodium hydroxide in small quantities for home use, [[Sodium carbonate| sodium carbonate]] is often used in place of sodium hydroxide<ref>{{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}}</ref>.
Specific foods processed with sodium hydroxide include:
* The [[Scandinavia]]n delicacy known as [[lutefisk]] (from ''lutfisk'', "lye fish").
* [[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]]. [[Nixtamal]] is similar, but uses [[calcium hydroxide]] instead of sodium hydroxide.
* Sodium hydroxide is also the chemical that causes gelling of egg whites in the production of [[Century egg]]s.
* German [[pretzel]]s are poached in a boiling sodium carbonate solution or cold sodium hydroxide solution before baking, which contributes to their unique crust.
* Most yellow coloured [[Chinese noodles]] are made with [[lye]]-water but are commonly mistaken for containing egg.
===Domestic uses===
Sodium hydroxide is used in the home as a drain cleaning agent for clearing clogged drains. It is distributed as a dry crystal or as a thick liquid gel. The chemical mechanism employed is the conversion of grease to a form of [[soap]]. Soap is water-soluble, and can be dissolved by flushing with water. Sodium hydroxide also decomposes complex molecules such as the [[protein]] that composes [[hair]]. Such '''drain cleaners''' (and their [[acid]]ic versions) are highly caustic and should be handled with care.
Sodium hydroxide has been used as a [[relaxer]] to [[straighten hair]]. However, because of the high incidence and intensity of chemical burns, chemical relaxer manufacturers have now switched to other alkaline chemicals, although sodium hydroxide relaxers are still available, used mostly by professionals.
===Tissue digestion===
This is a process that was used with farm animals at one time. This process involves the placing of a carcass into a sealed chamber, which then puts the carcass in a mixture of sodium hydroxide and water, which breaks chemical bonds keeping the body intact. This eventually turns the body into a coffee-like liquid, and the only solid remains are bone hulls, which could be crushed between one's fingertips. It is also of note that sodium hydroxide is frequently used in the process of decomposing [[roadkill]] dumped in landfills by animal disposal contractors{{Fact|date=February 2007}}.
Sodium hydroxide has also been used by criminals and [[serial killer]]s to dispose of their victims' bodies.<ref>[http://www.laportecounty.net/history/belle_gunness.html Belle Gunness]</ref>
===Illegal drugs===
Sodium hydroxide is a key reagent in the process of making [[methamphetamine]] and other illegal drugs. Contrary to popular media reports, it is not actually an "ingredient" in these drugs, but simply a strong base used to manipulate the pH at various points in a chemical synthesis.
=== Cleansing agent ===
Sodium hydroxide is frequently used as a cleaner in [[Brewery|breweries]], where it is simply called "caustic". It is added to water, heated, and then used to clean the large stainless steel tanks where beer is brewed, fermented, and stored. It can dissolve oils and protein-based deposits. A sodium hydroxide soak solution is used as a powerful degreaser on stainless and glass bakeware. It also the most common ingredient in oven cleaners.
==Safety==
Refer to a relevant Material Safety Data Sheet ([http://www.setonresourcecenter.com/msds/docs/wcd00046/wcd046de.htm MSDS]) before handling this material
Solid sodium hydroxide or solutions containing high concentrations of sodium hydroxide may cause [[chemical burn]]s, permanent injury or scarring, and [[blindness]].
[[solvation|Dissolution]] of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables.
Sodium hydroxide is extremely caustic, and can react with fats and oils on skin, in a reaction which creates salts. For this reason, sodium hydroxide is very dangerous, and skin should be washed thoroughly with water following contact with this substance.<!-- I thought that adding water was bad, shouldn't you wash it off with vinegar to counteract the alkalinity? --> {{Fact|date=June 2008}}
A solution of 0.5M or more of sodium hydroxide should be labelled corrosive, while a solution between 0.5-0.05M should be labelled irritant.{{Fact|date=May 2008}}
==See also==
* [[Common chemicals]]
* [[Soda lime]]
==External links==
* [http://www.certified-lye.com/ Certified Lye] - History, manufacture, first aid, storage, and safety of sodium hydroxide.
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc03/icsc0360.htm International Chemical Safety Card 0360]
* [http://www.cdc.gov/niosh/npg/npgd0565.html NIOSH Pocket Guide to Chemical Hazards]
* [http://ecb.jrc.it/ European Chemicals Bureau]
* [http://www.eurochlor.org/factsfigures Chlorine Online] - Facts about chlorine; sodium hydroxide is an important co-product of chlorine.
* [http://www.chlorineinstitute.org/ The Chlorine Institute, Inc. website]
* [http://www.bayermaterialsciencenafta.com/businesses/ibc/index.html Sodium hydroxide products of Bayer MaterialScience in North America]
* [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]
==References==
{{reflist}}
==General references==
# N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
# Heaton, A. (1996) ''An Introduction to Industrial Chemistry'', 3rd edition, New York:Blackie. ISBN 0-7514-0272-9.
# Kirk-Othmer Encyclopedia of Chemical Technology 5th edition ([http://www.mrw.interscience.wiley.com/kirk/kirk_articles_fs.html online], account needed), John Wiley & Sons. Accessed [[November 21]], [[2005]].
# Euro Chlor - How is chlorine made? [http://www.eurochlor.org/makingchlorine Chlorine Online]
[[Category:Bases]]
[[Category:Sodium compounds]]
[[Category:Household chemicals]]
[[Category:Inorganic compounds]]
[[Category:Hydroxides]]
[[Category:Deliquescent substances]]
[[Category:Desiccants]]
[[ar:هيدروكسيد صوديوم]]
[[bs:Natrijum hidroksid]]
[[bg:Натриева основа]]
[[ca:Hidròxid de sodi]]
[[cs:Hydroxid sodný]]
[[da:Natriumhydroxid]]
[[de:Natriumhydroxid]]
[[et:Naatriumhüdroksiid]]
[[es:Hidróxido de sodio]]
[[fr:Hydroxyde de sodium]]
[[gl:Hidróxido de sodio]]
[[ko:수산화 나트륨]]
[[it:Idrossido di sodio]]
[[he:נתרן הידרוקסידי]]
[[la:Lixivium]]
[[lv:Nātrija hidroksīds]]
[[lt:Natrio šarmas]]
[[hu:Nátrium-hidroxid]]
[[mk:Натриум хидроксид]]
[[nl:Natriumhydroxide]]
[[ja:水酸化ナトリウム]]
[[no:Natriumhydroksid]]
[[nn:Natriumhydroksid]]
[[nds:Natriumhydroxid]]
[[pl:Wodorotlenek sodu]]
[[pt:Hidróxido de sódio]]
[[ro:Hidroxid de sodiu]]
[[ru:Гидроксид натрия]]
[[simple:Sodium hydroxide]]
[[sk:Hydroxid sodný]]
[[sl:Natrijev hidroksid]]
[[fi:Natriumhydroksidi]]
[[sv:Natriumhydroxid]]
[[th:โซดาไฟ]]
[[tr:Sodyum hidroksit]]
[[uk:Гідроксид натрію]]
[[zh:氢氧化钠]]