Sodium hydroxide (
NaSodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...
OHIn chemistry, hydroxide is the name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known....
), also known as
lyeLye is a corrosive alkaline substance, commonly sodium hydroxide or historically potassium hydroxide . Previously, lye was among the many different alkalis leached from hardwood ashes...
and
caustic soda, is a caustic metallic
baseIn chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. Bases are also the oxides or hydroxides of metals. A soluble base is also often referred to as an alkali if hydroxide ions are involved. This refers to the Brønsted-Lowry theory of acids and bases...
. It is used in many industries, mostly as a strong
chemicalA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
basepH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
in the manufacture of
pulpPulp is a dry fibrous material prepared by chemically or mechanically separating fibers from wood, fiber crops or waste paper.Pulp can be either fluffy or formed into thick sheets. The latter form is used if the pulp must be transported from the pulp mill to a paper mill...
and
paperPaper is thin material mainly used for writing upon, printing upon or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
,
textileA textile is a flexible material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw wool fibres, linen, cotton, or other material on a spinning wheel to produce long strands...
s,
drinking waterDrinking water or potable water is water of sufficiently high quality that it can be consumed or used without risk of immediate or long term harm...
,
soapSoap is an anionic surfactant used in conjunction with water for washing and cleaning, which historically comes either in solid bars or in the form of a viscous liquid....
s and
detergentA detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning...
s and as a
drain cleanerDrain cleaner is a product dissolve clogs to unblock pipes, such as the drainpipes of sinks, bathtubs, toilets, and showers. Drain cleaners can be corrosive chemicals , or enzymatic formulations...
. Worldwide production in 1998 was around 45 million
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s. Sodium hydroxide is a common base in chemical laboratories.
Pure sodium hydroxide is a white solid; available in pellets, flakes, granules and as a 50% saturated solution. It is
hygroscopicHygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption.Hygroscopic substances include sugar, honey, glycerol, ethanol, methanol, sulfuric acid, methamphetamine, iodine, many chloride and hydroxide salts, and a...
and readily absorbs
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
from the air, so it should be stored in an airtight container. It is very soluble in water with liberation of heat. It also dissolves in
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
and
methanolMethanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with formula CH3OH . It is toxic: drinking 10 ml will cause blindness, and as little as 100 ml will cause death...
, though it exhibits lower solubility in these solvents than
potassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH. Along with sodium hydroxide, this colourless solid is a prototypical "strong base". It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive nature. In 2005, an...
. Molten sodium hydroxide is also a strong base, but the high temperature required limits applications. It is insoluble in
etherDiethyl ether, also known as ether, ethyl ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol...
and other non-polar solvents. A sodium hydroxide
solutionIn chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. Gases may dissolve in liquids, for example, carbon dioxide or oxygen in water. Liquids may dissolve in other liquids. Gases can...
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
2O. Which above 61.8°C are crystallized.
Chemical properties
Sodium hydroxide is completely ionic, containing sodium cations and
hydroxideIn chemistry, hydroxide is the name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known....
anions. The hydroxide anion makes sodium hydroxide a strong base which reacts with acids to form
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
and the corresponding salts, e.g., with
hydrochloric acidHydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong mineral acid and has major industrial uses. It is found naturally in gastric acid....
,
sodium chlorideSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
is formed:
- NaOH(aq) + HCl
Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong mineral acid and has major industrial uses. It is found naturally in gastric acid....
(aq) → NaClSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
(aq) + H2O(lLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
)
In general such neutralization reactions are represented by one simple net ionic equation:
- OH−
In chemistry, hydroxide is the name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known....
(aq) + H+The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H
+...
(aq) → H2OWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
(l)
This type of reaction with a strong acid, releases heat, and hence is referred to as
exothermicAn exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...
. Such acid-base reactions can also be used for
titrationTitration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant...
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 dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
has already been mentioned, but other acidic oxides such as
sulfur dioxideSulfur dioxide is the chemical compound with the formula SO
2. It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide...
(SO
2) also react completely. Such reactions are often used to "scrub" harmful acidic gases (like SO
2 and H
2S) and prevent their release into the atmosphere.
- 2NaOH + CO2
Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
→ Na2CO3Sodium carbonate , , is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate; and is domestically well known for its everyday use as a water softener...
+ H2O
Sodium hydroxide slowly reacts with glass to form
sodium silicateSodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and...
, so glass joints and
stopcockA stopcock is a valve used to restrict or isolate the flow of a liquid or gas through a pipe.In Great Britain a stopcock, not to be confused with a gate valve or a DiCiaccio branch, is used to prevent flow of water into a domestic water system. There are usually two stopcocks for a home...
s exposed to NaOH have a tendency to "freeze".
FlaskLaboratory flasks are vessels which fall into the category of laboratory equipment known as glassware. In laboratory and other scientific settings, they are usually referred to simply as flasks...
s and glass-lined
chemical reactorIn chemical engineering, chemical reactors are vessels designed to contain chemical reactions. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction...
s are damaged by long exposure to hot sodium hydroxide, and the glass becomes frosted. Sodium hydroxide does not attack
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
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
road tankerA tank truck or tanker lorry is a motor vehicle designed to carry liquefied loads, dry bulk cargo or gases on roads. The largest such vehicles are similar to railroad tank cars which are also designed to carry liquefied loads. Many variants exist due to the wide variety of liquids that can be...
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
(s) + 6NaOH
(aq) → 3H
2(g) + 2Na
3AlO
3(aq)
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 hydroxideAluminium hydroxide, Al3, is the most stable form of aluminium in normal conditions. It is found in nature as the mineral gibbsite and its three, much more rare, polymorphs: bayerite, doyleite and nordstrandite...
, used as a gelatinous
flocFlocculation is, in the field of chemistry, a process where colloids come out of suspension in the form of floc or flakes. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution.-Term...
to filter out particulate matter in
water treatmentWater treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the...
. Aluminium hydroxide is prepared at the treatment plant from
aluminium sulfateAluminium sulfate or Aluminium Sulphate, written as Al23 or Al2O12S3 Aluminium sulfate is an industrial chemical used as a flocculating agent in the purification of drinking water and waste water treatment plants, and also in paper...
by reacting with NaOH. This reaction is highly profitable, and is hence an important synthesis reaction.
Sodium hydroxide reacts readily with
carboxylic acidCarboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -COH, usually written -COOH or -CO2H. Carboxylic acids are Brønsted-Lowry acids — they are proton donors. Salts and anions of carboxylic acids are called...
s to form their salts and is even a strong enough base to form salts with
phenolPhenol, also known as carbolic acid, is a toxic, white crystalline solid. Its chemical formula is C6H5OH and its structure is that of a hydroxyl group bonded to a phenyl ring, making it an aromatic compound.-Phenols:...
s. NaOH can be used for the base-driven
hydrolysisHydrolysis is a chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions, which may go on to participate in further reactions. It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization...
of
esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s (as in
saponificationSaponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid . Saponification is commonly used to refer to the reaction of a metallic alkali with a fat or oil to form soap. Saponifiable substances are those that can be converted into...
),
amideIn chemistry, an amide is usually an organic compound that contains the functional group consisting of an acyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds...
s and alkyl halides. However, the limited solubility of NaOH in organic solvents means that the more soluble
KOHPotassium hydroxide is an inorganic compound with the formula KOH. Along with sodium hydroxide, this colourless solid is a prototypical "strong base". It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive nature. In 2005, an...
is often preferred.
Manufacture
In 1998, total world production was around 45 million
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s. North America and Asia collectively contributed around 14 million tonnes, while Europe produced around 10 million tonnes. In the United States, the major producer of sodium hydroxide is the
Dow Chemical CompanyThe Dow Chemical Company is an American multinational corporation headquartered in Midland, Michigan. As of 2007, it is the second largest chemical manufacturer in the world by revenue and as of February 2009, the third-largest chemical company in the world by market capitalization .Dow Chemical...
, which has annual production around 3.7 million
tonneA tonne or metric ton , also referred to as a metric tonne, is a measurement of mass equal to , or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI...
s from sites at
Freeport, TexasFreeport is a city in Brazoria County, Texas within the Houston–Sugar Land–Baytown Metropolitan Area and is situated in Southeast Texas. As of the 2000 U.S...
, and
Plaquemine, LouisianaPlaquemine is a city in and the parish seat of Iberville Parish, Louisiana, United States. The population was 7,064 at the 2000 census. It is part of the Baton Rouge Metropolitan Statistical Area....
. Other major US producers include Oxychem,
PPGPPG Industries is a global supplier of paints, coatings, optical products, specialty materials, chemicals, glass and fiber glass. The company has more than 140 manufacturing facilities and equity affiliates and operates in more than 60 countries. Sales in 2008 were $15.8 billion...
, Olin, Pioneer Companies (which was purchased by Olin), Inc. (PIONA), and
FormosaFormosa Plastics Group is a Taiwanese conglomerate of diverse interests, including biotechnology, petrochemical processing, and production of electronics components...
. All of these companies use the
chloralkali processA chloralkali process always implies the electrolysis of common salt or sodium chloride. Depending on the method several products beside hydrogen can be produced. If the products are separated, chlorine and sodium hydroxide are the products; by mixing, sodium hypochlorite or sodium chlorate are...
.
Methods of production
Sodium hydroxide is produced (along with
chlorineChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
and
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
) via the
chloralkali processA chloralkali process always implies the electrolysis of common salt or sodium chloride. Depending on the method several products beside hydrogen can be produced. If the products are separated, chlorine and sodium hydroxide are the products; by mixing, sodium hypochlorite or sodium chlorate are...
. This involves the
electrolysisIn chemistry and manufacturing, electrolysis is a method of using an electric current to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially highly important as a stage in the separation of elements from naturally-occurring sources such as ores using an electrolytic...
of an aqueous solution of
sodium chlorideSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
. The sodium hydroxide builds up at the
cathodeA cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .A widespread misconception is that cathode polarity is always negative...
, where water is reduced to hydrogen gas and
hydroxideIn chemistry, hydroxide is the name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known....
ion:
- 2Na+ + 2H2O + 2e− → H2 + 2NaOH
To produce NaOH it is necessary to prevent reaction of the NaOH with the
chlorineChlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
. 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
The Castner-Kellner process is a method of electrolysis on an aqueous alkali chloride solution to produce the corresponding alkali hydroxide, invented by American Hamilton Castner and Austrian Karl Kellner in the 1890s....
) – Sodium ions are reduced to sodium metalSodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...
, which forms an amalgamAn amalgam is a substance formed by the reaction of some other substance with mercury. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum...
with a mercuryMercury , also called quicksilver or hydrargyrum , is a chemical element with the symbol Hg and atomic number 80...
cathodeA cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .A widespread misconception is that cathode polarity is always negative...
; 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.
- Diaphragm cell process – uses a steel cathode, and the reaction of NaOH with Cl2 is prevented using a porous diaphragm
A diaphragm seal is a flexible membrane that seals and isolates an enclosure. The flexible nature of this seal allows pressure effects to cross the barrier but not the material being contained....
, often made of asbestos fibersAsbestos is a naturally occurring silicate mineral with long, thin fibrous crystals. The word asbestos is a borrowed Greek adjective meaning inextinguishable. The Greeks termed asbestos the miracle mineral because of its soft and pliant properties, as well as its ability to withstand...
. 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.
- Membrane cell process – similar to the diaphragm cell process, with a Nafion
Nafion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Walther Grot of DuPont. It is the first of a class of synthetic polymers with ionic properties which are called ionomers...
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).
An older method for sodium hydroxide production was the
Leblanc processThe Leblanc process was the industrial process for the production of soda ash used throughout the 19th century, named after its inventor, Nicolas Leblanc. It involved two stages: Production of sodium sulfate from sodium chloride, followed by reaction of the sodium sulfate with coal and calcium...
, which produced
sodium carbonateSodium carbonate , , is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate; and is domestically well known for its everyday use as a water softener...
, followed by roasting to create
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
and
sodium oxideSodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses. Treatment with water affords sodium hydroxide.The alkali metal oxides M2O crystallise in the antifluorite structure...
. This method is still occasionally used. It helped establish sodium hydroxide as an important commodity chemical.
The LeBlanc process was superseded by the
Solvay processThe Solvay process, also referred to as the ammonia-soda process, is the major industrial process for the production of soda ash . The ammonia-soda process was developed into its modern form by Ernest Solvay during the 1860s...
in the late 19th century.
Uses
Sodium hydroxide is the principal strong
baseIn chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. Bases are also the oxides or hydroxides of metals. A soluble base is also often referred to as an alkali if hydroxide ions are involved. This refers to the Brønsted-Lowry theory of acids and bases...
used in the chemical industry. In bulk it is most often handled as an aqueous
solutionIn chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. Gases may dissolve in liquids, for example, carbon dioxide or oxygen in water. Liquids may dissolve in other liquids. Gases can...
, since solutions are cheaper and easier to handle. It is used to drive chemical reactions and also for the
neutralizationIn chemistry, neutralization, or neutralisation is a chemical reaction whereby an acid and a base react to form water and a salt....
of acidic materials. It can be used also as a neutralizing agent in petroleum refining. It is also used for heavy duty and industrial cleaning.
Alumina production
In the
Bayer processThe Bayer process is the principal industrial means of refining bauxite to produce alumina.Bauxite, the most important ore of aluminium, contains only 30-54% alumina, Al2O3, the rest being a mixture of silica, various iron oxides, and titanium dioxide. The alumina must be...
, sodium hydroxide is used in the refining of alumina containing ore (
bauxiteBauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al
3, boehmite γ-AlO, and diaspore α-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO
2...
) to produce alumina (aluminium oxide) which is the raw material used to produce
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
metal via the electrolytic Hall-Héroult process.
Soap production
Sodium hydroxide is traditionally used in soap making (cold process soap,
saponificationSaponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid . Saponification is commonly used to refer to the reaction of a metallic alkali with a fat or oil to form soap. Saponifiable substances are those that can be converted into...
)..It was made in the ninteenth century for a hard suface rather than liquid product because it was easier to store and ship.
Oil drilling
Sodium hydroxide is used as an additive in
drilling mud to increase
alkalinityAlkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity of a solution and ANC is often incorrectly used to refer to alkalinity.The alkalinity is...
. This serves two functions. Firstly raising
alkalinityAlkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity of a solution and ANC is often incorrectly used to refer to alkalinity.The alkalinity is...
in
bentoniteBentonite is an absorbent aluminium phyllosilicate, generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na, Ca, and Al. As noted in several places in the geologic literature, there are some...
mud systems increases the mud
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms , viscosity is "thickness." Thus, water is "thin," having a lower viscosity, while honey is "thick," having a higher viscosity...
. A secondary function of raising
alkalinityAlkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity of a solution and ANC is often incorrectly used to refer to alkalinity.The alkalinity is...
is to neutralise any
acid gasAcid gas is natural gas or any other gas mixture which contains significant amounts of hydrogen sulfide , carbon dioxide , or similar contaminants. The terms acid gas and sour gas are often incorrectly treated as synonyms...
(such as hydrogen sulphide and
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
) which may be encountered in the geological formation as drilling progresses.
Fuel production
Sodium hydroxide can be added to poor quality crude oil to remove sulphurous impurities in a process known as
caustic washing. The process forms a highly toxic waste which containing hydrogen sulphide, organic disulphides and mercaptans. Because of this the process is banned in many countries but in 2006,
TrafiguraTrafigura is a Swiss-based multinational company founded in 1993 trading in base metals and energy, including oil. it had equity of more than US$2bn and a turnover of US$73bn that generated US$440 million of profit....
used the process and then dumped the waste in Africa.
Pulp manufacturing for producing paper
Sodium hydroxide was also widely used in making paper. Along with
sodium sulfideSodium sulfide is the name used to refer to the chemical compound Na
2S but more commonly its hydrate Na
2S
.9H
2O. Both are colorless water-soluble salts that give strongly alkaline solutions...
, NaOH is a key component of the white liquor solution used to separate
ligninLignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
from
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
fiberFiber, also spelled fibre, is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread. They are very important in the biology of both plants and animals, for holding tissues together. Human uses for fibers are diverse...
s in the
Kraft processThe kraft process describes a technology for conversion of wood into wood pulp consisting of almost pure cellulose fibers...
. It also plays a key role in several later stages of the process of
bleaching the brown pulpBleaching of wood pulp is the chemical processing carried out on various types of wood pulp to decrease the color of the pulp, so that it becomes whiter. The main use of wood pulp is to make paper where whiteness is an important characteristic...
resulting from the pulping process. These stages include
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
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.
Biodiesel
For the manufacture of
biodieselBiodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl esters. Biodiesel is typically made by chemically reacting lipids with an alcohol....
, sodium hydroxide is used as a catalyst for the
transesterificationIn organic chemistry, transesterification is the process of exchanging the organic group R" of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base....
of methanol and triglycerides. This only works with
anhydrousAs a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another.-Solvents:...
sodium hydroxide, because combined with water the fat would turn into
soapSoap is an anionic surfactant used in conjunction with water for washing and cleaning, which historically comes either in solid bars or in the form of a viscous liquid....
, which would be tainted with
methanolMethanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with formula CH3OH . It is toxic: drinking 10 ml will cause blindness, and as little as 100 ml will cause death...
. It is used more often than
potassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH. Along with sodium hydroxide, this colourless solid is a prototypical "strong base". It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive nature. In 2005, an...
because it is cheaper and a smaller quantity is needed.
Aluminium etching
Strong bases attack
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
. Sodium hydroxide reacts with aluminium and water to create hydrogen gas. The aluminium takes the oxygen atom from sodium hydroxide(NaOH), which in turn takes the oxygen atom from the water, and releases the two hydrogen atoms. In this reaction, sodium hydroxide acts as an active catalyst. This reaction can be useful in etching through a resist, removing anodizing, or converting a polished surface to a satin-like finish, but without further
passivationPassivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and...
such as anodizing or alodining the surface may become degraded, either under normal use or in severe atmospheric conditions.
Cleaning agent
Sodium hydroxide is frequently used as an industrial
cleaning agentCleaning Agents are substances, usually liquids, that are used to remove dirt, including dust, stains, bad smells and clutter on surfaces. Purposes of cleaning agents include health, beauty, absence of offensive odor, avoidance of shame, and to avoid the spreading of dirt and contaminants to...
where it is often called "caustic". It is added to water, heated, and then used to clean the process equipent, storage tanks, etc. It can dissolve
greaseThe term grease is used to describe a number of semisolid lubricants possessing a higher initial viscosity than oil. Although the word grease is also used to describe rendered fat of animals, in the context of lubricants, it typically applies to a material consisting of a calcium, sodium or...
, oils,
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s and
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
based deposits. The sodium hydroxide solution might also be added surfactants to stabilize dissolved substances to prevent redeposition. A sodium hydroxide soak solution is used as a powerful degreaser on stainless and glass bakeware. It is also a common ingredient in oven cleaners.
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.
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 that 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
roadkillRoadkill is an animal or animals that have been struck and killed by motor vehicles. Mammals are the animals most likely to be recorded as roadkill...
dumped in landfills by animal disposal contractors.
Sodium hydroxide has also been used by criminals to dispose of their victims' bodies
Food preparation
Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables,
chocolateChocolate comprises a number of raw and processed foods produced from the seed of the tropical cacao tree. Cacao has been cultivated for at least three millennia in Mexico, Central and South America, with its earliest documented use around 1100 BC...
and
cocoaCocoa is the dried and fully fermented fatty seed of the cacao tree, from which chocolate is made. "Cocoa" can often also refer to the drink commonly known as hot chocolate; to cocoa powder, the dry powder made by grinding cocoa seeds and removing the cocoa butter from the dark, bitter cocoa...
processing, caramel coloring production,
poultryPoultry is the category of domesticated birds that people keep for the purpose of collecting their eggs, or killing for their meat and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as...
scalding,
soft drinkA soft drink is a drink that does not contain alcohol . Soft drinks are often carbonated and commonly consumed while cold. The most common soft drinks are colas, flavored water, sparkling water, iced tea, sweet tea, lemonade, squash and fruit punch....
processing, and thickening
ice creamIce cream or ice-cream is a frozen dessert usually made from dairy products, such as milk and cream, combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners. In some cases, artificial flavourings and colorings are used in...
.
OliveThe Olive is a species of a small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean Basin, from Lebanon, Syria and the maritime parts of Turkey and northern Iran at the south end of the Caspian Sea...
s are often soaked in sodium hydroxide to soften them, while
pretzelA pretzel is a bread pastry of Medieval European origin that has the shape of a three looped knot or twisted braid. Pretzels are either soft or hard. Hard pretzels have evolved into a variety of shapes from knotted loops to straight "pretzel sticks"...
s and
GermanGermany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium,...
lye rollthumb|right|Typical lye roll.Lye rolls are a baked specialty in Germany , Austria, and Switzerland. They are made by glazing bread rolls with a lye solution before baking...
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 carbonateSodium carbonate , , is a sodium salt of carbonic acid. It most commonly occurs as a crystalline heptahydrate, which readily effloresces to form a white powder, the monohydrate; and is domestically well known for its everyday use as a water softener...
is often used in place of sodium hydroxide.
Specific foods processed with sodium hydroxide include:
- The Scandinavia
Scandinavia is a geographical region in northern Europe that includes, and is named after, the Scanian Province. It consists of the kingdoms of Norway, Sweden, and Denmark...
n delicacy known as lutefiskLutefisk is a traditional dish of the Nordic countries made from stockfish or dried/salted whitefish and soda lye...
(from lutfisk, "lye fish").
- Hominy
Hominy or nixtamal is dried maize kernels which have been treated with an alkali.The traditional U.S. version involves soaking dried corn in lye-water , traditionally derived from wood ash, until the hulls are removed.Mexican recipes describe a preparation process consisting primarily of cooking in...
is dried maizeMaize , is a herbaceous plant domesticated in Mesoamerica and subsequently spread throughout the American continents...
(corn) kernels reconstituted by soaking in lyeLye is a corrosive alkaline substance, commonly sodium hydroxide or historically potassium hydroxide . Previously, lye was among the many different alkalis leached from hardwood ashes...
-water. These expand considerably in size and may be further processed by frying to make corn nuts or by drying and grinding to make gritsGrits is an aboriginal American corn-based food common in the Southern United States, consisting of coarsely ground corn.Grits is similar to other thick maize-based porridges from around the world such as polenta. It also has a resemblance to farina, a thinner porridge. The word leads back to the...
. Nixtamal is similar, but uses calcium hydroxideCalcium hydroxide, traditionally called slaked lime, hydrated lime, slack lime, or pickling lime, is a chemical compound with the chemical formula Ca2. It is a colourless crystal or white powder, and is obtained when calcium oxide is mixed, or "slaked" with water...
instead of sodium hydroxide.
- Sodium hydroxide is also the chemical that causes gelling of egg whites in the production of Century egg
Century egg, also known as preserved egg, hundred-year egg, thousand-year egg, and thousand-year-old egg, is a Chinese cuisine ingredient made by preserving duck, chicken or quail eggs in a mixture of clay, ash, salt, lime, and rice straw for several weeks to several months, depending on the method...
s.
- German pretzel
A pretzel is a bread pastry of Medieval European origin that has the shape of a three looped knot or twisted braid. Pretzels are either soft or hard. Hard pretzels have evolved into a variety of shapes from knotted loops to straight "pretzel sticks"...
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
Chinese noodles are an essential ingredient and staple in Chinese cuisine. There is a great variety of noodles, which vary according to their region of production, ingredients, shape or width, and manner of preparation....
are made with lyeLye is a corrosive alkaline substance, commonly sodium hydroxide or historically potassium hydroxide . Previously, lye was among the many different alkalis leached from hardwood ashes...
-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
soapSoap is an anionic surfactant used in conjunction with water for washing and cleaning, which historically comes either in solid bars or in the form of a viscous liquid....
. Soap is water-soluble, and can be dissolved by flushing with water. This conversion occurs far more rapidly at high temperatures, so commercial drain cleaners may also contain chemicals that react with water to generate heat. Sodium hydroxide also decomposes complex molecules such as the
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
that composes
hairHair is a protein filament that grows through the epidermis from follicles deep within the dermis. The fine, soft hair found on many nonhuman mammals is typically called fur; wool is the characteristically curly hair found on sheep and goats. Found exclusively in mammals, hair is one of the...
. Such
drain cleaners (and their
acidAn acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0...
ic versions) are highly caustic and should be handled with care.
Sodium hydroxide has been used as a
relaxerA relaxer is a type of lotion or cream which makes hair less curly, and easier to straighten by chemically "relaxing" the natural curls. The active agent is usually a strong alkali, although some formulations are based on ammonium thioglycolate instead....
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.
Use in chemical analysis
In
analytical chemistryAnalytical chemistry is the study of the chemical composition of natural and artificial materials. Properties studied in analytical chemistry include geometric features such as molecular morphologies and distributions of species, as well as features such as composition and species identity...
, sodium hydroxide solutions are often used to measure the
concentrationIn chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent.To...
of acids by
titrationTitration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant...
. Since NaOH is not a
primary standardIn metrology, a primary standard is a standard that is accurate enough that it is not calibrated by or subordinate to other standards. Primary standards are used to calibrate other standards.-In chemistry:...
, solutions must first be standardised by titration against a standard such as
KHPPotassium hydrogen phthalate, often called simply KHP, is a white or colorless, ionic solid that is the monopotassium salt of phthalic acid. The hydrogen is slightly acidic, and it is often used as a primary standard for acid-base titrations because it is solid and air-stable, making it easy to...
.
BuretteA burette is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap, or stopcock, on the bottom. It is used to dispense known amounts of a liquid reagent in experiments for which such precision is necessary, such as a titration...
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 cations in
Qualitative Inorganic AnalysisClassical qualitative inorganic analysis is a method of analytical chemistry which seeks to find elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, so that materials in other forms may need to be brought into this state before using standard...
, as well as to provide alkaline media for some reactions that need it, such as the
BiuretBiuret is a condensation compound of urea, equivalent to two molecules of urea less one of ammonia. It is a white solid soluble in hot water and decomposes at 186–189 °C...
test.
Safety
Solid sodium hydroxide or solutions of sodium hydroxide will cause
chemical burnA chemical burn occurs when living tissue is exposed to a corrosive substance such as a strong acid or base. Chemical burns follow standard burn classification and may cause extensive tissue damage. The main types of irritant and/or corrosive products are: acids, bases, oxidizers, solvents,...
s, permanent injury or scarring, and
blindnessBlindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
if it contacts unprotected human or animal tissue. Protective equipment such as rubber gloves, safety clothing and
eye protectionSee section safety in article glasses for more detailed information about safety for glasses.Eye protection is protective gear for the eyes, which comes in many types depending upon the threat that is to be reduced...
should always be used when handling the material or its solutions.
DissolutionSolvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
of sodium hydroxide is highly
exothermicIn thermodynamics, the term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light , electricity , or sound. Its etymology stems from the Greek prefix ex- and the Greek word thermein...
, and the resulting heat may cause heat burns or ignite flammables.
See also
- HAZMAT Class 8 Corrosive Substances
A corrosive material is a liquid or solid that causes full thickness destruction of human skin at the site of contact within a specified period of time. A liquid that has a severe corrosion rate on steel or aluminum based on the criteria in 49CFR 173.137 is also a corrosive material.-Divisions:454...
- Common chemicals
- Table of common chemical ingredients and where to find them :...
- List of cleaning agents
External links
http://www.encyclopedia.com/topic/sodium_hydroxide.aspx