Sodium hydroxide

Sodium hydroxide

Overview
Sodium hydroxide also known as lye
Lye
Lye 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 base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...

. It is used in many industries, mostly as a strong chemical
Chemical compound
A 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...

 base
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 in the manufacture of pulp
Wood pulp
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...

 and paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing 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....

, textile
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

s, drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

, soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

s and detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

s and as a drain cleaner
Drain cleaner
A drain cleaner is a consumer product or device that unblocks sewer pipes or helps to prevent the occurrence of clogged drains; the term may also refer to the individual who performs the activity...

. Worldwide production in 2004 was approximately 60 million tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s, while demand was 51 million tonnes.

Pure sodium hydroxide is a white solid available in pellets, flakes, granules, and as a 50% saturated solution.
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Encyclopedia
Sodium hydroxide also known as lye
Lye
Lye 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 base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...

. It is used in many industries, mostly as a strong chemical
Chemical compound
A 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...

 base
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 in the manufacture of pulp
Wood pulp
Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking.-History:...

 and paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing 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....

, textile
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

s, drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

, soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

s and detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

s and as a drain cleaner
Drain cleaner
A drain cleaner is a consumer product or device that unblocks sewer pipes or helps to prevent the occurrence of clogged drains; the term may also refer to the individual who performs the activity...

. Worldwide production in 2004 was approximately 60 million tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s, while demand was 51 million tonnes.

Pure sodium hydroxide is a white solid available in pellets, flakes, granules, and as a 50% saturated solution. It is hygroscopic
Hygroscopy
Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing material becoming physically 'changed,' somewhat, by an increase in volume, stickiness, or other...

 and readily absorbs carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 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 ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 and methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

, though it exhibits lower solubility in these solvents than does potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...

. Molten sodium hydroxide is also a strong base, but the high temperature required limits applications. It is insoluble in ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

 and other non-polar solvents. A sodium hydroxide solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

 will leave a yellow stain on fabric and paper.

Properties


Sodium hydroxide is predominantly ionic, containing sodium cations and hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 anions. The hydroxide anion makes sodium hydroxide a strong base which reacts with acids to form water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and the corresponding salts.

ΔH°dissolution for aqueous dilution is −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/cm3. The standard enthalpy change of formation (ΔH°form) is −734.95 kJ / mol.

Reactions


With acids
Sodium hydroxide reacts with protic acids to give water and the corresponding salts. For example, with hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

, sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic 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
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

(aq) → NaCl
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic 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(l
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

)


In general such neutralization reactions are represented by one simple net ionic equation:
OH
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

(aq) + H+
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

(aq) → H2O
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

(l)


This type of reaction with a strong acid releases heat, and hence is referred to as exothermic
Exothermic reaction
An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...

. Such acid-base reactions can also be used for titration
Titration
Titration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the...

s. However, sodium hydroxide is not used as a primary standard
Primary standard
A primary standard in metrology is a standard that is accurate enough that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are used to calibrate other standards referred to as working...

 because it is hygroscopic and absorbs carbon dioxide from air.

Sodium hydroxide reacts readily with carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s to form their salts and is even a strong enough base to form salts with phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...

s. It is not, however, strong enough to quantitatively produce enolates from carbonyl compounds or deprotonate amines; this would require a superbase
Superbase
In chemistry, a superbase is an extremely strong base, that is a compound that has a high affinity for protons. Hydroxide ion is the strongest base possible in aqueous solutions, but bases exist with pKb's well outside of the aqueous range. Such bases are valuable in organic synthesis and are...

.

With acidic oxides
Sodium hydroxide also reacts with acidic oxides, such as sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

. Such reactions are often used to "scrub
Scrubber
Scrubber systems are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. Traditionally, the term "scrubber" has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream...

" harmful acidic gases (like SO2 and H2S) produced in the burning of coal and thus prevent their release into the atmosphere. For example,
2 NaOH + CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 → Na2CO3
Sodium carbonate
Sodium carbonate , Na2CO3 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. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 + H2O


With amphoteric metals and oxides
Sodium hydroxide slowly reacts with glass to form sodium silicate
Sodium silicate
Sodium 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 automobiles...

, so glass joints and stopcock
Stopcock
A 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". Flask
Laboratory flask
Laboratory 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 reactor
Chemical reactor
In 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 iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 since iron does not have amphoteric properties (i.e., it only dissolves in acid, not base). A few transition metals, however, may react vigorously with sodium hydroxide.

In 1986, an aluminium road tanker
Tank truck
A tank truck or road tanker 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...

 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:
2 Al + 2 NaOH + 2 H2O → 2 NaAlO2 + 3 H2


Precipitant
Unlike NaOH, the hydroxides of most transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...

s are insoluble, and therefore sodium hydroxide can be used to precipitate transition metal hydroxides.

Aluminium hydroxide
Aluminium hydroxide
Aluminium hydroxide, Al3, ATH, sometimes erroneously called Hydrate of alumina, is found in nature as the mineral gibbsite and its three, much more rare forms, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO, and aluminium oxide, Al2O3,...

 is used as a gelatinous flocculant to filter out particulate matter in water treatment
Water treatment
Water 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 sulfate
Aluminium sulfate
Aluminium sulfate, alternatively spelt aluminum sulfate, aluminium sulphate, or aluminum sulphate; is a chemical compound with the formula Al23...

 by reacting it with NaOH.
Al2(SO4)3 + 6 NaOH → 2 Al(OH)3 + 3 Na2SO4


Saponification
NaOH can be used for the base-driven hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of ester
Ester
Esters 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 saponification
Saponification
Saponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...

), amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...

s and alkyl halides. However, the limited solubility of NaOH in organic solvents means that the more soluble KOH
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...

 is often preferred.

Electrolysis
In the laboratory, with careful control of conditions, sodium metal can be isolated from the electrolysis of the molten monohydrate in a low temperature version of the Castner process
Castner Process
The Castner process is a process for manufacturing sodium metal by electrolysis of molten sodium hydroxide at approximately 330°C. Below that temperature the melt would solidify, above that temperature, the metal would start to dissolve in the melt....

, according to the following reaction:
4 NaOH·H2O(l) → 4 Na(l) + O2(g) + 6 H2O(g)


The monohydrate does not need to be heated in order to melt, as the process produces enough heat due to ohmic heating. However, it must be initiated with a small quantity of liquid water to create an electrically conductive electrolyte. As the system's temperature increases, the monohydrate will start to melt at about 65 °C as stated above. Only when the temperature reaches about 100 °C can sodium be isolated. Below this temperature, the water produced will react with the sodium, above this point, any water formed will be driven off in the vapour phase, creating an essentially anhydrous reaction. While this process has some advantages over other electrolytic processes, it is not preferred by most chemists for several reasons: a marginal quantity of sodium produced boils at the electrode interface, the vapour thus given off consists primarily of fumed sodium oxide, which tends to settle on any surface in close proximity with corrosive consequences.

Production


Sodium hydroxide is industrially produced as a 50 % solution by variations of the electrolytic chloralkali process
Chloralkali process
The chloralkali process is an industrial process for the electrolysis of sodium chloride solution . 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...

. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water. Solid sodium hydroxide is most commonly sold as flakes, prill
Prill
A prill is a small aggregate of a material, most often a dry sphere, formed from a melted liquid. The material to be prilled must be a solid at room temperature and a low viscosity liquid when melted. Prills are formed by allowing drops of the melted prill substance to congeal or freeze in mid-air...

s, and cast blocks.

In 2004, world production was estimated at 60 million dry metric tonnes of sodium hydroxide, and demand was estimated at 51 million tonnes. In 1998, total world production was around 45 million tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units 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 Company
Dow Chemical Company
The Dow Chemical Company is a multinational corporation headquartered in Midland, Michigan, United States. 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...

, which has annual production around 3.7 million tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

s from sites at Freeport
Freeport, Texas
Freeport 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...

, Texas, and Plaquemine
Plaquemine, Louisiana
Plaquemine 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....

, Louisiana. Other major US producers include Oxychem, PPG
PPG Industries
PPG Industries is a global supplier of paints, coatings, optical products, specialty materials, chemicals, glass and fiber glass. With headquarters in Pittsburgh, Pennsylvania, PPG operates in more than 60 countries around the globe. Sales in 2010 were $13.4 billion...

, Olin, Pioneer Companies (which was purchased by Olin), Inc. (PIONA), and Formosa
Formosa Plastics Group
Formosa 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 process
Chloralkali process
The chloralkali process is an industrial process for the electrolysis of sodium chloride solution . 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...

.

Of historic interest is the Leblanc process
Leblanc process
The 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 carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 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. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

, followed by roasting to create carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and sodium oxide
Sodium oxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

, which readily absorbs water to create sodium hydroxide. 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
Solvay process
The 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.
Na2CO3 → Na2O + CO2
Na2O + H2O → 2 NaOH


Sodium hydroxide may be formed by the metathesis reaction between calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic 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. It has many names including hydrated lime, builders lime, slack lime, cal, or...

 (also known as lime) and sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 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. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 (also known as soda ash):
Ca(OH)2 + Na2CO3 → CaCO3 + 2 NaOH

Chloralkali electrolysis




Sodium hydroxide is produced (along with chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

) via the chloralkali process
Chloralkali process
The chloralkali process is an industrial process for the electrolysis of sodium chloride solution . 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...

. This involves the electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 of an aqueous solution of sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic 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 cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

, where water is reduced to hydrogen gas and hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 ion:
2 Na+ + 2 H2O + 2 e → H2 + 2 NaOH


More accurately:
2 Na+Cl + 2 H2O + 2 e → H2 + 2 Cl + 2 NaOH


The Cl ions are oxidized to chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 gas at the anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

.

To produce NaOH it is necessary to prevent reaction of the NaOH with the chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

. 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
    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 metal
    Sodium
    Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

    , which forms an amalgam
    Amalgam (chemistry)
    An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

     with a mercury
    Mercury (element)
    Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

     cathode
    Cathode
    A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not 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
    Diaphragm seal
    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 fibers
    Asbestos
    Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

    . 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
    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).

Uses



Sodium hydroxide is the principal strong base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...

 used in the chemical industry. In bulk it is most often handled as an aqueous solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

, since solutions are cheaper and easier to handle. Sodium hydroxide, a strong base, is responsible for most of these applications. Another strong base such as potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...

 is likely to yield positive results as well.

56 % of sodium hydroxide produced is used by the chemical industry, with 25 % of the same total used by the paper industry. Sodium hydroxide is also used for the manufacture of sodium salts and detergents, for pH regulation, and for organic synthesis. It is used in the Bayer process
Bayer process
The 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 purified before it can...

 of aluminium production.

Sodium hydroxide is used in many scenarios where it is desirable to increase the alkalinity of a mixture, or to neutralize acids.

For example, sodium hydroxide is used as an additive in drilling mud to increase alkalinity
Alkalinity
Alkalinity or AT measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution...

 in bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...

 mud systems increases the mud viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

, as well as to neutralise any acid gas
Acid gas
Acid 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 sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

) which may be encountered in the geological formation as drilling progresses.

In the same industry, poor quality crude oil can be treated with sodium hydroxide to remove sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

ous impurities in a process known as caustic washing. As above, sodium hydroxide reacts with weak acids such as hydrogen sulfide and mercaptans to give the 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
Trafigura
Trafigura is an Amsterdam-based multinational company founded in 1993 trading in base metals and energy, including oil. the company had equity of more than $2 billion and a turnover of $73 billion that generated $440 million of profit....

 used the process and then dumped the waste in Africa.

Paper making



Sodium hydroxide was also widely used in making paper. Along with sodium sulfide
Sodium sulfide
Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...

, NaOH is a key component of the white liquor solution used to separate lignin
Lignin
Lignin 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 cellulose
Cellulose
Cellulose 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....

 fiber
Fiber
Fiber 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....

s in the Kraft process
Kraft process
The 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 pulp
Bleaching of wood pulp
Bleaching 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 oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 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.

Tissue digestion


In a similar fashion, sodium hydroxide is used to digest tissues, such 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 coffee-like liquid, and the only solid that remains are bone hulls, which could be crushed between one's fingertips. Sodium hydroxide is frequently used in the process of decomposing roadkill
Roadkill
Roadkill is an animal or animals that have been struck and killed by motor vehicles. In the United States of America, removal and disposal of animals struck by motor vehicles is usually the responsibility of the state's state trooper association or department of transportation.-History:During the...

 dumped in landfills by animal disposal contractors.

Dissolving amphoteric metals and compounds


Strong bases attack aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

. Sodium hydroxide reacts with aluminium and water to release 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, The reaction thus produces hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas and sodium aluminate
Sodium aluminate
Sodium aluminate is an important commercial inorganic chemical. It works as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate is a white crystalline solid having a formula variously given as NaAlO2, NaAl4 , Na2O·Al2O3, or Na2Al2O4...

. In this reaction, sodium hydroxide acts as an agent to make the solution alkaline, which aluminium can dissolve in. This reaction can be useful in etching, removing anodizing, or converting a polished surface to a satin-like finish, but without further passivation
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...

 such as anodizing or alodining the surface may become degraded, either under normal use or in severe atmospheric conditions.

In the Bayer process
Bayer process
The 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 purified before it can...

, sodium hydroxide is used in the refining of alumina containing ores (bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...

) to produce alumina (aluminium oxide) which is the raw material used to produce aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 metal via the electrolytic
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 Hall-Héroult process
Hall-Héroult process
The Hall–Héroult process is the major industrial process for the production of aluminium. It involves dissolving alumina in molten cryolite, and electrolysing the molten salt bath to obtain pure aluminium metal.-Process:...

. Since the alumina is amphoteric, it dissolves in the sodium hydroxide, leaving impurities less soluble at high pH such as iron oxides behind in the form of a highly alkaline red mud
Red mud
Red mud is a solid waste product of the Bayer process, the principal industrial means of refining bauxite in order to provide alumina as raw material for the electrolysis of aluminium by the Hall–Héroult process. A typical plant produces one to two times as much red mud as alumina...

.

Other amphoteric metals are zinc and lead which dissolve in concentrated sodium hydroxide solutions to give sodium zincate
Sodium zincate
Sodium zincate refers to anionic zinc oxides or hydroxides, depending on conditions. In the applications of these materials, the exact formula is not necessarily important and it is likely that aqueous zincate solutions consist of mixtures.-Hydroxyzincates:...

 and sodium plumbate respectively.

Esterification and transesterification reagent


Sodium hydroxide is traditionally used in soap making (cold process soap, saponification
Saponification
Saponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...

). It was made in the nineteenth century for a hard surface rather than liquid product because it was easier to store and transport.

For the manufacture of biodiesel
Biodiesel
Biodiesel 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 transesterification
Transesterification
In 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 catalyst...

 of methanol and triglycerides. This only works with anhydrous
Anhydrous
As 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...

 sodium hydroxide, because combined with water the fat would turn into soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

, which would be tainted with methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

. It is used more often than potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...

 because it is cheaper and a smaller quantity is needed.

Cleaning agent



Sodium hydroxide is frequently used as an industrial cleaning agent
Cleaning agent
Cleaning 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 avoidance of 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 equipment, storage tanks, etc. It can dissolve grease
Grease (lubricant)
The term grease is used to describe semisolid lubricants. Although the word grease is also used to describe rendered fat of animals, in the context of lubrication, grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil...

, oils, fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...

s and protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 based deposits. It is also used for cleaning waste discharge pipes under sinks and drains in domestic properties. Surfactants can be added to the sodium hydroxide solution in order to stabilize dissolved substances and thus prevent redeposition. A sodium hydroxide soak solution is used as a powerful degreaser on stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

 and glass bakeware. It is also a common ingredient in oven cleaners.

A common use of sodium hydroxide is in the production of parts washer
Parts washer
A parts washer is a piece of equipment used to remove contaminants or debris, such as dirt, grime, carbon, oil, grease, metal chips, cutting fluids, mold release agents, ink, paint, and corrosion from workpieces...

 detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...

s. Parts washer detergents based on sodium hydroxide are some of the most aggressive parts washer cleaning chemicals. The sodium hydroxide based detergent 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 when trichloroethane
1,1,1-Trichloroethane
The organic compound 1,1,1-trichloroethane, also known as methyl chloroform, is a chloroalkane. This colourless, sweet-smelling liquid was once produced industrially in large quantities for use as a solvent...

 was outlawed by the Montreal Protocol
Montreal Protocol
The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion...

. Water and sodium hydroxide detergent based parts washers are considered to be an environmental improvement over the solvent based cleaning methods.

Food preparation


Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables, chocolate
Chocolate
Chocolate is a raw or processed food produced from the seed of the tropical Theobroma cacao tree. Cacao has been cultivated for at least three millennia in Mexico, Central and South America. Its earliest documented use is around 1100 BC...

 and cocoa processing, caramel coloring production, poultry
Poultry
Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...

 scalding, soft drink
Soft drink
A soft drink is a non-alcoholic beverage that typically contains water , a sweetener, and a flavoring agent...

 processing, and thickening ice cream
Ice cream
Ice cream is a frozen dessert usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners...

. Olive
Olive
The olive , Olea europaea), is a species of a small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean Basin as well as northern Iran at the south end of the Caspian Sea.Its fruit, also called the olive, is of major agricultural importance in the...

s are often soaked in sodium hydroxide for softening; or, if soaked longer, for transformation into black olives. Pretzel
Pretzel
A pretzel is a type of baked food made from dough in soft and hard varieties and savory or sweet flavors in a unique knot-like shape, originating in Europe...

s and German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 lye roll
Lye roll
thumb|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. Owing to the difficulty in obtaining food grade sodium hydroxide in small quantities for home use, sodium carbonate
Sodium carbonate
Sodium carbonate , Na2CO3 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. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

 is often used in place of sodium hydroxide.

Specific foods processed with sodium hydroxide include:
  • The Pinoy
    Pinoy
    Pinoy is an informal demonym referring to the Filipino people in the Philippines and overseas Filipinos around the world. Filipinos usually refer to themselves as Pinoy or sometimes the feminine Pinay...

     or Filipino dessert (kakanin) called kutsinta uses a bit of lye water to help give the rice flour batter a jelly like consistency.
  • A similar process is also used in the kakanin known as pitsi-pitsi or pichi-pichi (pit-chi-pit-chi) except that the mixture uses grated cassava
    Cassava
    Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...

     instead of rice flour.
  • The Scandinavia
    Scandinavia
    Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...

    n delicacy known as lutefisk
    Lutefisk
    Lutefisk or Lutfisk is a traditional dish of the Nordic countries and parts of the Midwest United States. It is made from aged stockfish or dried/salted whitefish and lye . It is gelatinous in texture, and has an extremely strong, pungent odor...

     (from lutfisk, "lye fish").
  • Hominy
    Hominy
    Hominy or nixtamal is dried maize kernels which have been treated with an alkali in a process called nixtamalization.The English term hominy is derived from the Powhatan language word for maize. Many other Native American cultures also made hominy and integrated it into their diet...

     is dried maize
    Maize
    Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

     (corn) kernels reconstituted by soaking in lye
    Lye
    Lye 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 grits
    Grits
    Grits are a food of American Indian origin common in the Southern United States and mainly eaten at breakfast. They consist of coarsely ground corn, or sometimes alkali-treated corn . They are also sometimes called sofkee or sofkey from the Muskogee language word...

    . Nixtamal is similar, but uses calcium hydroxide
    Calcium hydroxide
    Calcium hydroxide, traditionally called slaked lime, is an inorganic 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. It has many names including hydrated lime, builders lime, slack lime, cal, or...

     instead of sodium hydroxide.
  • Sodium hydroxide is also the chemical that causes gelling of egg whites in the production of Century egg
    Century egg
    Century egg or pidan , also known as preserved egg, hundred-year egg, thousand-year egg, thousand-year-old egg, and millennium egg, is a Chinese cuisine ingredient made by preserving duck, chicken or quail eggs in a mixture of clay, ash, salt, lime, and rice hulls for several weeks to several...

    s.
  • German pretzel
    Pretzel
    A pretzel is a type of baked food made from dough in soft and hard varieties and savory or sweet flavors in a unique knot-like shape, originating in Europe...

    s are poached in a boiling sodium carbonate
    Sodium carbonate
    Sodium carbonate , Na2CO3 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. Sodium carbonate is domestically well-known for its everyday use as a water softener. It can be extracted from the...

     solution or cold sodium hydroxide solution before baking, which contributes to their unique crust.
  • Lye-water is an essential ingredient in the crust of the traditional baked Chinese moon cakes.
  • Most yellow coloured Chinese noodles
    Chinese noodles
    Noodles are an essential ingredient and staple in Chinese cuisine. There is a great variety of Chinese noodles, which vary according to their region of production, ingredients, shape or width, and manner of preparation...

     are made with lye
    Lye
    Lye 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.
  • Black olives result from normal (green) olives being subjected to a lye-based chemical bath.

Domestic uses


Sodium hydroxide is used in the home as a drain cleaning agent
Drain cleaner
A drain cleaner is a consumer product or device that unblocks sewer pipes or helps to prevent the occurrence of clogged drains; the term may also refer to the individual who performs the activity...

 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
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...

. 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
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

. Sodium hydroxide also decomposes complex molecules such as the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that composes hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

. Such drain cleaners and their acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

ic versions are highly caustic and should be handled with care.

Sodium hydroxide is used in some relaxer
Relaxer
A relaxer is a type of lotion or cream generally used by people with afro textured hair, which makes hair less curly and also easier to straighten by chemically "relaxing" the natural curls...

s to straighten hair. However, because of the high incidence and intensity of chemical burns, manufacturers of chemical relaxers use other alkaline chemicals in preparations available to average 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.

Safety



Solid sodium hydroxide or solutions of sodium hydroxide may cause chemical burn
Chemical burn
A 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 if it contacts unprotected human, or other animal, tissue. It may cause blindness
Blindness
Blindness 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 the eye. Protective equipment such as rubber gloves, safety clothing and eye protection
Eye protection
Eye protection is protective gear for the eyes, which comes in many types depending upon the threat that is to be reduced. The threats can be particles, light, wind blast, heat, sea spray or some type of ball or puck used in sports...

 should always be used when handling the material or its solutions.

Dissolution
Solvation
Solvation, 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 exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

, and the resulting heat may cause heat burns or ignite flammables. It also produces heat when reacted with acids. Sodium hydroxide is corrosive to some metals, e.g. aluminum, which produces flammable hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas on contact. Sodium hydroxide is also mildly corrosive to glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

, which can cause damage to glazing
Glazing
Glazing, which derives from the Middle English for 'glass', is a part of a wall or window, made of glass. Glazing also describes the work done by a professional "glazier"...

 or freezing of ground glass joint
Ground glass joint
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may be rapidly fitted together to reflux a reaction mixture...

s.



See also

  • HAZMAT Class 8 Corrosive Substances
    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
    Common chemicals
    - Table of common chemical ingredients and where to find them :...

  • List of elemental cleaning agents

External links