LIQUID CAUSTIC

Liquid caustic is a highly effective alkaline solution widely used for pH control, neutralization, cleaning, and chemical processing.
Liquid caustic's excellent water miscibility and strong reactivity make it suitable for water treatment, detergents, pulp and paper, textiles, and industrial manufacturing.
Liquid caustic provides efficient process performance in applications requiring rapid alkalinity adjustment, degreasing, and saponification.

CAS Number: 1310-73-2
EC Number: 215-185-5
Molecular Formula: NaOH
Molecular Weight: 40.00 g/mol

Synonyms: Liquid Caustic Soda, Caustic Soda Solution, Sodium Hydroxide Solution, Liquid Sodium Hydroxide, Aqueous Sodium Hydroxide, NaOH Solution, Caustic Lye, Soda Lye, Lye Solution, Liquid Lye, Sodium Hydrate Solution, Caustic Alkali Solution, Sodium Hydroxide Aqueous Solution, Industrial Caustic Soda Solution, Liquid Alkali, Caustic Soda Liquor, Sodium Hydroxide Liquor, Liquid NaOH, 50% Caustic Soda Solution, 32% Caustic Soda Solution

Liquid Caustic, commonly known as Sodium Hydroxide Solution or Caustic Soda Solution, is a strongly alkaline aqueous solution of sodium hydroxide.
Liquid caustic is generally supplied as a clear, colorless liquid in various concentrations, commonly around 25%, 32%, 45%, or 50% NaOH depending on industrial requirements.

Liquid caustic is widely used for pH adjustment, neutralization, cleaning, degreasing, saponification, chemical synthesis, and process control.
Liquid Caustic is extensively applied in water and wastewater treatment, pulp and paper production, textile processing, soap and detergent manufacturing, petroleum refining, food processing under permitted conditions, and numerous chemical manufacturing operations.

Because dissolution and dilution can release significant heat, Liquid Caustic should be handled carefully with suitable corrosion-resistant equipment and appropriate personal protective measures.

Pure Liquid caustic is a colorless, crystalline solid that melts at 318 °C without decomposition.
Liquid caustic is highly soluble in water, has a lower solubility in ethanol and methanol, but is insoluble in ether and other non-polar solvents.

Similar to the hydration of sulfuric acid, dissolving solid Liquid caustic in water is an extremely exothermic reaction in which a large amount of heat is released, posing a safety hazard due to the possibility of splashing.
The resulting solution is usually colorless and odorless.
As with other alkaline solutions, Liquid caustic becomes slippery upon contact with skin.

Liquid caustic reacts with protic acids to produce water and associated salts.

For example, when Liquid caustic reacts with hydrochloric acid, sodium chloride is formed:
NaOH (aqueous) + HCl (aqueous) → NaCl (aq) + H₂O (l)

Generally, such neutralization reactions are represented by a simple net ionic equation:
OH⁻ (aq) + H⁺ (aqueous) → H₂O (l)

This type of reaction with a strong acid releases heat and is therefore exothermic.
These acid-base reactions can also be used for titrations.
However, Liquid caustic is not used as a primary standard because it is hygroscopic and absorbs carbon dioxide from the air.

Caustic soda is a white, hygroscopic substance.
Liquid caustic readily dissolves in water, forming a soft, slippery, and soapy-feeling solution.

Liquid caustic has an irritating effect on human tissue.
In the laboratory, Liquid caustic is used to capture acidic gases such as CO2.

Liquid caustic is used in industry for the production of many chemicals, in the artificial silk, soap, paper, paint, and detergent industries, and in petroleum refineries.
When it reacts with water, Liquid caustic's temperature rises to 50 degrees Celsius in about 5 minutes and remains hot for about 15 minutes.

Liquid caustic is an inorganic compound with the formula NaOH.
Liquid caustic is a white solid ionic compound consisting of sodium cations Na+ and hydroxide anions OH−.
As a strong nucleophile, Liquid caustic is frequently used in SN2 reactions.

Liquid caustic is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures, and may cause severe chemical burns at high concentrations.
Liquid caustic is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air.

Liquid caustic forms a series of hydrates NaOH·nH2O.
The monohydrate NaOH·H2O crystallizes from water solutions between 12.3 and 61.8 °C.
Liquid caustic is often this monohydrate, and published data may refer to it instead of the anhydrous compound.

As one of the simplest hydroxides, Liquid caustic is frequently used alongside neutral water and acidic hydrochloric acid to demonstrate the pH scale to chemistry students.[14]

Liquid caustic is used in many industries: in the making of wood pulp and paper, textiles, drinking water, soaps and detergents, and as a drain cleaner.
Worldwide production in 2022 was approximately 83 million tons.

Uses of Liquid Caustic:
Liquid caustic is a popular strong base used in industry.
Liquid caustic is used in the manufacture of sodium salts and detergents, pH regulation, and organic synthesis.
In bulk, Liquid caustic is most often handled as an aqueous solution since solutions are cheaper and easier to handle.

Liquid caustic is used in many scenarios where it is desirable to increase the alkalinity of a mixture, or to neutralize acids.
For example, in the petroleum industry, Liquid caustic is used as an additive in drilling mud to increase alkalinity in bentonite mud systems, to increase the mud viscosity, and to neutralize any acid gas (such as hydrogen sulfide and carbon dioxide) which may be encountered in the geological formation as drilling progresses.

Another use is in salt spray testing where pH needs to be regulated.
Liquid caustic is used with hydrochloric acid to balance pH.
The resultant salt, NaCl, is the corrosive agent used in the standard neutral pH salt spray test.

Poor quality crude oil, particularly of the sour variety, can be treated with Liquid caustic to remove sulfurous impurities in a process known as caustic washing.
Liquid caustic reacts with weak acids such as hydrogen sulfide and thiols to yield non-volatile sodium salts, which can be removed.

The waste which is formed is toxic and difficult to deal with, and the process is banned in many countries because of this.
In 2006, Trafigura used the process and then dumped the waste in Ivory Coast.

Other common uses of Liquid caustic include:
Liquid caustic is used for making soaps and detergents.
Liquid caustic is used for hard bar soap, while potassium hydroxide is used for liquid soaps.

Liquid caustic is used more often than potassium hydroxide because it is cheaper and a smaller quantity is needed.
Liquid caustic is used as drain cleaners that convert pipe-clogging fats and grease into soap, which dissolves in water.

Liquid caustic is used for making artificial textile fibres such as rayon.
Liquid caustic is used in the manufacture of paper. Around 56% of sodium hydroxide produced is used by industry, 25% of which is used in the paper industry.

Liquid caustic is used in purifying bauxite ore from which aluminium metal is extracted.
This is known as the Bayer process.

Liquid caustic is used for oil refining.
Liquid caustic is used for making dyes and bleaches.
Liquid caustic is used in water treatment plants for pH regulation.

Chemical pulping:
Liquid caustic is also widely used in pulping of wood for making paper or regenerated fibers.
Along with sodium sulfide, Liquid caustic is a key component of the white liquor solution used to separate lignin from cellulose fibers in the kraft process.

Liquid caustic also plays a key role in several later stages of the process of bleaching the brown pulp resulting from the pulping process.
These stages include oxygen 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, Liquid caustic is used to digest tissues, as in a process that was used with farm animals at one time.
This process involved placing a carcass into a sealed chamber, then adding a mixture of sodium hydroxide and water (which breaks the chemical bonds that keep the flesh intact).
This eventually turns the body into a liquid with a dark brown color and the only solids that remain are bone hulls, which can be crushed between one's fingertips.

Liquid caustic is frequently used in the process of decomposing roadkill dumped in landfills by animal disposal contractors.
Due to its availability and low cost, Liquid caustic has been used by criminals to dispose of corpses.

Italian serial killer Leonarda Cianciulli used this chemical to turn dead bodies into soap.
In Mexico, a man who worked for drug cartels admitted disposing of over 300 bodies with it.

Liquid caustic is a dangerous chemical due to its ability to hydrolyze protein.
If a dilute solution is spilled on the skin, burns may result if the area is not washed thoroughly and for several minutes with running water.
Splashes in the eye can be more serious and can lead to blindness.

Dissolving amphoteric metals and compounds:
Strong bases attack aluminium.
Liquid caustic reacts with aluminium and water to release hydrogen gas.

The aluminium takes an oxygen atom from Liquid caustic, which in turn takes an oxygen atom from water, and releases two hydrogen atoms.
The reaction thus produces hydrogen gas and sodium aluminate.
In this reaction, Liquid caustic acts as an agent to make the solution alkaline, which aluminium can dissolve in.

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

Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications.
Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO2, Na3AlO3, Na[Al(OH)4], Na2O·Al2O3 or Na2Al2O4.

Formation of sodium tetrahydroxoaluminate(III) or hydrated sodium aluminate is given by:
2 Al + 2 NaOH + 6 H2O → 2 Na[Al(OH)4] + 3 H2

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

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

Other amphoteric metals are zinc and lead which dissolve in concentrated Liquid caustic solutions to give sodium zincate and sodium plumbate respectively.

Esterification and transesterification reagent:
Liquid caustic is traditionally used in soap making (cold process soap, saponification).
Liquid caustic 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, Liquid caustic is used as a catalyst for the transesterification of methanol and triglycerides.
This only works with anhydrous Liquid caustic, because combined with water the fat would turn into soap, which would be tainted with methanol.
Due to production costs, Liquid caustic, which is produced using common salt, is cheaper than potassium hydroxide.

Skincare ingredient:
Liquid caustic is an ingredient used in some skin care and cosmetic products, such as facial cleansers, creams, lotions, and makeup. 
Liquid caustic is typically used in low concentration as a pH balancer, due its highly alkaline nature.

Food preparation:
Food uses of Liquid caustic include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel coloring production, poultry scalding, soft drink processing, and thickening ice cream.
Olives are often soaked in Liquid caustic for softening; pretzels and German lye rolls are glazed with a sodium hydroxide solution before baking to make them crisp.

Owing to the difficulty in obtaining food grade Liquid caustic in small quantities for home use, sodium carbonate is often used in place of Liquid caustic.
Liquid caustic is known as E number E524.

Specific foods processed with Liquid caustic include:
German pretzels are poached in a boiling sodium carbonate solution or cold Liquid caustic solution before baking, which contributes to their unique crust.
Lye water is an essential ingredient in the crust of the traditional baked Chinese moon cakes.

Most yellow coloured Chinese noodles are made with lye water but are commonly mistaken for containing egg.
One variety of zongzi uses lye water to impart a sweet flavor.

Liquid caustic causes gelling of egg whites in the production of century eggs.
Some methods of preparing olives involve subjecting them to a lye-based brine.

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

The Norwegian dish known as lutefisk (Norwegian: lutfisk, lit. 'lye fish').
Bagels are often boiled in a lye solution before baking, contributing to their shiny crust.

Hominy is dried maize (corn) kernels reconstituted by soaking in lye-water.
These expand considerably in size and may be further processed by frying to make corn nuts or by drying and grinding to make grits.

Hominy is used to create masa, a popular flour used in Mexican cuisine to make corn tortillas and tamales.
Nixtamal is similar, but uses calcium hydroxide instead of Liquid caustic.

Cleaning agent:
Liquid caustic is frequently used as an industrial cleaning agent, where it is often called "caustic".
Liquid caustic is added to water, heated, and then used to clean process equipment, storage tanks, and other things.

Liquid caustic can dissolve grease, oils, fats and protein-based deposits.
Liquid caustic is also used for cleaning waste discharge pipes under sinks and drains in domestic properties.

Surfactants can be added to the Liquid caustic solution in order to stabilize dissolved substances and thus prevent redeposition.
A Liquid caustic soak solution is used as a powerful degreaser on stainless steel and glass bakeware.
Liquid caustic is also a common ingredient in oven cleaners.

A common use of Liquid caustic is in the production of parts washer detergents.
Parts washer detergents based on Liquid caustic are some of the most aggressive parts washer cleaning chemicals. 

The Liquid caustic-based detergents include surfactants, rust inhibitors and defoamers.
A parts washer heats water and the detergent in a closed cabinet and then sprays the heated Liquid caustic and hot water at pressure against dirty parts for degreasing applications.

Liquid caustic used in this manner replaced many solvent-based systems in the early 1990s when trichloroethane was outlawed by the Montreal Protocol.
Water and Liquid caustic detergent-based parts washers are considered to be an environmental improvement over the solvent-based cleaning methods.

Liquid caustic is used in the home as a type of drain openers to unblock clogged drains, usually in the form of a dry crystal or as a thick liquid gel.
The alkali reacts with greases to produce water soluble soap and glycerol.

Liquid caustic also hydrolyzes proteins, such as those found in hair, which may block waste water pipes.
Dissolving Liquid caustic in water is an exothermic reaction producing considerable quantities of heat which assists in speeding up the reactions with grease and other organic matter.
Such alkaline drain cleaners and their acidic versions are highly corrosive and should be handled with great caution.

Relaxer:
Liquid caustic is used in some relaxers to straighten hair.
However, because of the high incidence and intensity of chemical burns, manufacturers of chemical relaxers use other alkaline chemicals in preparations available to consumers.
Liquid caustic relaxers are still available, but they are used mostly by professionals.

Paint stripper:
A solution of Liquid caustic in water was traditionally used as the most common paint stripper on wooden objects.
Liquid caustic's use has become less common, because it can damage the wood surface, raising the grain and staining the colour.

Water treatment:
Liquid caustic is sometimes used during water purification to raise the pH of water supplies.
Increased pH makes the water less corrosive to plumbing and reduces the amount of lead, copper and other toxic metals that can dissolve into drinking water.

Historical uses:
Liquid caustic has been used for detection of carbon monoxide poisoning, with blood samples of such patients turning to a vermilion color upon the addition of a few drops of Liquid caustic.
Today, carbon monoxide poisoning can be detected by CO oximetry.

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

Applications of Liquid Caustic:
Liquid caustic is used in acid control, odor removal, pipe cleaning, pH balancing).
Liquid caustic is used as an adhesive, in heat-sensitive printing, in newsprint).

Liquid caustic is used in the production of Sodium Aluminate, Sodium Cyanide, Silicate, Polycarbonate, Titanium Oxide, Zeolite).
Liquid caustic is used in removing residues from the final product, bleaching).

Liquid caustic is used in the production of STTP, Sodium Hypochlorite, Soap, Oven and Pipe Cleaner).
Liquid caustic is used in the production of Sodium Phenolate [aspirin and antiseptic]).

Liquid caustic is used in refining edible oil, peeling fruits and vegetables, freezing).
Liquid caustic is used in oil cleaning, water purification, equipment cleaning).

Liquid caustic is used in the manufacture of Label Adhesives together with Starch, Caustic Soda, Water, Silicate).
Liquid caustic is used in the manufacture of Corrugated Cardboard Glue together with Starch, Caustic Soda, Water, Borax).

Liquid caustic is used in removing acid residues from refined products, extracting phenols, balancing pH in drilling mud, drilling) In removing calcium and bacteria.
Liquid caustic is used in filter cleaning (in filter pools) and cleaning acid units in mines.

Liquid caustic is used in addition, caustic soda (sodium hydroxide) or lime (calcium hydroxide) is used to adjust the pH value of sodium cyanide.
Liquid caustic is used in acid control, odor removal, pipe cleaning, pH balancing).

Liquid caustic is used as an adhesive, in heat-sensitive printing, in newsprint)
Liquid caustic is used in the production of Sodium Aluminate, Sodium Cyanide, Silicate, Polycarbonate, Titanium Oxide, Zeolite).

Liquid caustic is used in removing residues in the final product, in bleaching.
Liquid caustic is used in the production of STTP, Sodium Hypochlorite, Soap, Oven and Pipe Cleaner).

Liquid caustic is used in the production of Sodium Phenolate [aspirin and antiseptic].
Liquid caustic is used in refining edible oil, peeling fruits and vegetables, freezing.

Liquid caustic is used in oil cleaning, water purification, equipment cleaning.
Liquid caustic is used also in adjusting the pH value of Sodium Cyanide used Caustic Soda (Sodium Hydroxide) or Lime Calcium hydroxide is used.

Properties of Liquid Caustic:
Liquid caustic's physical appearance is a colorless liquid.
Liquid caustic is heavier than water in density.

This means Liquid caustic is more viscous than water in terms of viscosity.
Liquid caustic's density is 1.515 g/ml at 20 °C.

Liquid caustic is an odorless chemical.
The boiling point is 130 °C.

The melting point is 0 °C.
Liquid caustic is a very strong base.
Liquid caustic has the ability to dissolve in water, alcohol, and glycerol.

Physical properties:
Pure Liquid caustic is a colorless crystalline solid that melts at 318 °C (604 °F) without decomposition and boils at 1,388 °C (2,530 °F).
Liquid caustic is highly soluble in water, with a lower solubility in polar solvents such as ethanol and methanol.
Liquid caustic is insoluble in ether and other non-polar solvents.

Similar to the hydration of sulfuric acid, dissolution of solid Liquid caustic in water is a highly exothermic reaction where a large amount of heat is liberated, posing a threat to safety through the possibility of splashing.
The resulting solution is usually colorless and odorless.
As with other alkaline solutions, Liquid caustic feels slippery with skin contact due to the process of saponification that occurs between NaOH and natural skin oils.

Viscosity:
Concentrated (50%) aqueous solutions of Liquid caustic have a characteristic viscosity, 78 mPa·s, that is much greater than that of water (1.0 mPa·s) and near that of olive oil (85 mPa·s) at room temperature.
The viscosity of aqueous NaOH, as with any liquid chemical, is inversely related to its temperature, i.e., its viscosity decreases as temperature increases, and vice versa.
The viscosity of Liquid caustic solutions plays a direct role in its application as well as its storage.

Hydrates:
Liquid caustic can form several hydrates NaOH·nH2O, which result in a complex solubility diagram that was described in detail by Spencer Umfreville Pickering in 1893.

The known hydrates and the approximate ranges of temperature and concentration (mass percent of NaOH) of their saturated water solutions are:
Heptahydrate, NaOH·7H2O: from −28 °C (18.8%) to −24 °C (22.2%).
Pentahydrate, NaOH·5H2O: from −24 °C (22.2%) to −17.7 °C (24.8%).

Tetrahydrate, NaOH·4H2O, α form: from −17.7 °C (24.8%) to 5.4 °C (32.5%).
Tetrahydrate, NaOH·4H2O, β form: metastable.

Trihemihydrate, NaOH·3.5H2O: from 5.4 °C (32.5%) to 15.38 °C (38.8%) and then to 5.0 °C (45.7%).
Trihydrate, NaOH·3H2O: metastable.

Dihydrate, NaOH·2H2O: from 5.0 °C (45.7%) to 12.3 °C (51%).
Monohydrate, NaOH·H2O: from 12.3 °C (51%) to 65.10 °C (69%) then to 62.63 °C (73.1%).
Early reports refer to hydrates with n = 0.5 or n = 2/3, but later careful investigations failed to confirm their existence.

The only hydrates with stable melting points are NaOH·H2O (65.10 °C) and NaOH·3.5H2O (15.38 °C).
The other hydrates, except the metastable ones NaOH·3H2O and NaOH·4H2O (β) can be crystallized from solutions of the proper composition.
However, solutions of NaOH can be easily supercooled by many degrees, which allows the formation of hydrates (including the metastable ones) from solutions with different concentrations.

For example, when a solution of NaOH and water with 1:2 mole ratio (52.6% NaOH by mass) is cooled, the monohydrate normally starts to crystallize (at about 22 °C) before the dihydrate.
However, the solution can easily be supercooled down to −15 °C, at which point Liquid caustic may quickly crystallize as the dihydrate.

When heated, the solid dihydrate might melt directly into a solution at 13.35 °C; however, once the temperature exceeds 12.58 °C it often decomposes into solid monohydrate and a liquid solution.
Even the n = 3.5 hydrate is difficult to crystallize, because the solution supercools so much that other hydrates become more stable.

A hot water solution containing 73.1% (mass) of NaOH is a eutectic that solidifies at about 62.63 °C as an intimate mix of anhydrous and monohydrate crystals.
A second stable eutectic composition is 45.4% (mass) of NaOH, that solidifies at about 4.9 °C into a mixture of crystals of the dihydrate and of the 3.5-hydrate.

The third stable eutectic has 18.4% (mass) of NaOH.
Liquid caustic solidifies at about −28.7 °C as a mixture of water ice and the heptahydrate NaOH·7H2O.

When solutions with less than 18.4% NaOH are cooled, water ice crystallizes first, leaving the NaOH in solution.
The α form of the tetrahydrate has density 1.33 g/cm3.

Liquid caustic melts congruously at 7.55 °C into a liquid with 35.7% NaOH and density 1.392 g/cm3, and therefore floats on it like ice on water.
However, at about 4.9 °C Liquid caustic may instead melt incongruously into a mixture of solid NaOH·3.5H2O and a liquid solution.

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

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

Crystal structure:
NaOH and its monohydrate form orthorhombic crystals with the space groups Cmcm (oS8) and Pbca (oP24), respectively.
The monohydrate cell dimensions are a = 1.1825, b = 0.6213, c = 0.6069 nm.

The atoms are arranged in a hydrargillite-like layer structure, with each sodium atom surrounded by six oxygen atoms, three each from hydroxide ions and three from water molecules.
The hydrogen atoms of the hydroxyls form strong bonds with oxygen atoms within each O layer.
Adjacent O layers are held together by hydrogen bonds between water molecules.

Chemical properties:

Reaction with acids:
Liquid caustic reacts with protic acids to produce water and the corresponding salts.

For example, when Liquid caustic reacts with hydrochloric acid, sodium chloride is formed:
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

In general, such neutralization reactions are represented by one simple net ionic equation:
OH−(aq) + H+(aq) → H2O(l)

This type of reaction with a strong acid releases heat, and hence is exothermic.
Such acid–base reactions can also be used for titrations.
However, Liquid caustic is not used as a primary standard because it is hygroscopic and absorbs carbon dioxide from air.

Reaction with acidic oxides:
Liquid caustic also reacts with acidic oxides, such as sulfur dioxide.
Such reactions are often used to "scrub" 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 + SO2 → Na2SO3 + H2O

Reaction with metals and oxides:
Glass reacts slowly with aqueous Liquid caustic solutions at ambient temperatures to form soluble silicates.
Because of this, glass joints and stopcocks exposed to Liquid caustic have a tendency to "freeze".

Flasks and glass-lined chemical reactors are damaged by long exposure to hot Liquid caustic, which also frosts the glass.
Liquid caustic does not attack iron at room temperature, since iron does not have amphoteric properties (i.e., it only dissolves in acid, not base).

Nevertheless, at high temperatures (e.g. above 500 °C), iron can react endothermically with Liquid caustic to form iron(III) oxide, sodium metal, and hydrogen gas.
This is due to the lower enthalpy of formation of iron(III) oxide (−824.2 kJ/mol) compared to Liquid caustic (−500 kJ/mol) and positive entropy change of the reaction, which implies spontaneity at high temperatures (ΔST > ΔH, ΔG < 0) and non-spontaneity at low temperatures (ΔST < ΔH, ΔG > 0).

Consider the following reaction between molten Liquid caustic and finely divided iron filings:
4 Fe + 6 NaOH → 2 Fe2O3 + 6 Na + 3 H2

A few transition metals, however, may react quite vigorously with Liquid caustic under milder conditions.

In 1986, an aluminium road tanker in the UK was mistakenly used to transport 25% Liquid caustic solution causing pressurization of the contents and damage to tankers.

The pressurization is due to the hydrogen gas which is produced in the reaction between Liquid caustic and aluminium:
2 Al + 2 NaOH + 6 H2O → 2 Na[Al(OH)4] + 3 H2

Precipitant:
Unlike Liquid caustic, which is soluble, the hydroxides of most transition metals are insoluble, and therefore Liquid caustic can be used to precipitate transition metal hydroxides.

The following colours are observed:
Copper – blue
Iron(II) – green
Iron(III) – yellow/brown

Zinc and lead salts dissolve in excess Liquid caustic to give a clear solution of Na2ZnO2 or Na2PbO2.

Aluminium hydroxide is used as a gelatinous flocculant to filter out particulate matter in water treatment.
Aluminium hydroxide is prepared at the treatment plant from aluminium sulfate by reacting it with Liquid caustic or bicarbonate.

Al2(SO4)3 + 6 NaOH → 2 Al(OH)3 + 3 Na2SO4
Al2(SO4)3 + 6 NaHCO3 → 2 Al(OH)3 + 3 Na2SO4 + 6 CO2

Saponification:
Liquid caustic can be used for the base-driven hydrolysis of esters (also called saponification), amides and alkyl halides.
However, the limited solubility of Liquid caustic in organic solvents means that the more soluble potassium hydroxide (KOH) is often preferred.

Touching a Liquid caustic solution with bare hands, while not recommended, produces a slippery feeling.
This happens because oils on the skin such as sebum are converted to soap.
Despite solubility in propylene glycol, Liquid caustic is unlikely to replace water in saponification due to propylene glycol's primary reaction with fat before reaction between Liquid caustic and fat.

Production of Liquid Caustic:
Liquid caustic is industrially produced, first as a 32% solution, and then evaporated to a 50% solution by variations of the electrolytic chloralkali process.
Chlorine gas is the main by-product from this process.

Solid sodium hydroxide is obtained from this solution by the evaporation of water.
Solid sodium hydroxide is most commonly sold as flakes, prills, and cast blocks.

In 2022, world production was estimated at 83 million dry tonnes of Liquid caustic, and demand was estimated at 51 million tonnes.
In 1998, total world production was around 45 million tonnes.

North America and Asia each contributed around 14 million tonnes, while Europe produced around 10 million tonnes.
In the United States, the major producer of Liquid caustic is Olin, which has annual production around 5.7 million tonnes from sites at Freeport, Texas; Plaquemine, Louisiana; St. Gabriel, Louisiana; McIntosh, Alabama; Charleston, Tennessee; Niagara Falls, New York; and Bécancour, Canada.

Other major US producers include Oxychem, Westlake, Shintech, and Formosa.
All of these companies use the chloralkali process.

Historically, Liquid caustic was produced by treating sodium carbonate with calcium hydroxide (slaked lime) in a metathesis reaction which takes advantage of the fact that Liquid caustic is soluble, while calcium carbonate is not.
This process was called causticizing.

Ca(OH)2(aq) + Na2CO3(s) → CaCO3(s) + 2 NaOH(aq)

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

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

2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)

This reaction is commonly used for demonstrating the reactivity of alkali metals in academic environments; however, Liquid caustic is not used commercially aside from a reaction within the mercury cell chloralkali process where sodium amalgam is reacted with water.

History of Liquid Caustic:
Liquid caustic was first prepared by soap makers.
A procedure for making Liquid caustic appeared as part of a recipe for making soap in an Arab book of the late 13th century: Al-mukhtara' fi funun min al-suna' (Inventions from the Various Industrial Arts), which was compiled by al-Muzaffar Yusuf ibn 'Umar ibn 'Ali ibn Rasul (d. 1295), a king of Yemen.

The recipe called for passing water repeatedly through a mixture of alkali (Arabic: al-qily, where qily is ash from saltwort plants, which are rich in sodium; hence alkali was impure sodium carbonate) and quicklime (calcium oxide, CaO), whereby a solution of Liquid caustic was obtained.
European soap makers also followed this recipe.

When in 1791 the French chemist and surgeon Nicolas Leblanc (1742–1806) patented a process for mass-producing sodium carbonate, natural "soda ash" (impure sodium carbonate that was obtained from the ashes of plants that are rich in sodium)[57]: p36  was replaced by this artificial version.
However, by the 20th century, the electrolysis of sodium chloride had become the primary method for producing Liquid caustic.

Stability and Reactivity of Liquid Caustic:

Chemical Stability:
Stable under recommended storage and handling conditions.

Reactivity:
Reacts strongly with acids and may react with certain metals to release flammable hydrogen gas.

Conditions to Avoid:
Excessive heat, uncontrolled dilution, contact with incompatible substances, and reactive metals.

Incompatible Materials:
Strong acids, ammonium salts, aluminum, zinc, tin, and other reactive metals.

Handling and Storage of Liquid Caustic:

Safe Handling:
Avoid contact with skin, eyes, and clothing and prevent splashing or mist formation.

Storage Conditions:
Store tightly closed in a cool, dry, well-ventilated area using corrosion-resistant containers and equipment.

First Aid Measures of Liquid Caustic:

Inhalation:
Move the affected person to fresh air and seek medical attention if irritation or breathing difficulty occurs.

Skin Contact:
Immediately rinse with plenty of water and remove contaminated clothing.

Eye Contact:
Rinse immediately with plenty of water for at least 15 minutes and obtain urgent medical attention.

Ingestion:
Rinse mouth, do not induce vomiting, and seek immediate medical attention.

Firefighting Measures of Liquid Caustic:

Suitable Extinguishing Media:
Use extinguishing media appropriate for the surrounding fire.

Specific Hazards:
Product is non-flammable, but contact with certain metals may generate flammable hydrogen gas.

Protective Equipment:
Firefighters should wear chemical-resistant protective clothing and self-contained breathing apparatus where necessary.

Accidental Release Measures of Liquid Caustic:

Personal Precautions:
Avoid direct contact, splashing, and mist inhalation and wear appropriate protective equipment.

Cleanup Methods:
Contain the spill, absorb with suitable inert material where appropriate, and transfer to a corrosion-resistant waste container.

Environmental Precautions:
Prevent significant quantities from entering drains, soil, or surface waters.

Exposure Controls/Personal Protection of Liquid Caustic:

Engineering Controls:
Provide adequate ventilation, eyewash stations, and emergency safety showers.

Eye Protection:
Wear tightly fitting chemical safety goggles and face protection where splash exposure is possible.

Hand Protection:
Wear suitable alkali-resistant chemical gloves.

Skin Protection:
Wear chemical-resistant protective clothing and footwear.

Respiratory Protection:
Use suitable respiratory protection where mist or aerosol exposure cannot be adequately controlled.

Identifiers of Liquid Caustic:
Chemical Name: Sodium Hydroxide Solution
Common Name: Liquid Caustic
CAS Number: 1310-73-2
EC Number: 215-185-5
UN Number: UN 1824
Molecular Formula: NaOH
Molecular Weight: 40.00 g/mol
IUPAC Name: Sodium hydroxide

Chemical Formula: NaOH
CAS No: 1310-73-2
EC No: 215-185-5 
UN No: 1824
HS Code: 28151200

CAS Number: 1310-73-2
ChEBI: CHEBI:32145
ChemSpider: 14114
ECHA InfoCard: 100.013.805
EC Number: 215-185-5
E number: E524 (acidity regulators, ...)
Gmelin Reference: 68430
KEGG: D01169
MeSH: Sodium+Hydroxide
PubChem CID: 14798
RTECS number: WB4900000
UNII: 55X04QC32I
UN number: 1823 (solid), 1824 (solution)
CompTox Dashboard (EPA): DTXSID0029634
InChI: InChI=1S/Na.H2O/h;1H2/q+1;/p-1
Key: HEMHJVSKTPXQMS-UHFFFAOYSA-M 
InChI=1/Na.H2O/h;1H2/q+1;/p-1
Key: HEMHJVSKTPXQMS-REWHXWOFAM
SMILES: [OH-].[Na+]

Properties of Liquid Caustic:
Chemical formula: NaOH
Molar mass: 39.997 g·mol−1
Appearance: White, opaque crystals
Odor: odorless
Density: 2.13 g/cm3
Melting point: 323 °C (613 °F; 596 K)
Boiling point: 1,388 °C (2,530 °F; 1,661 K)
Solubility in water: 418 g/L (0 °C)
1000 g/L (25 °C)
3370 g/L (100 °C)
Solubility: soluble in glycerol, negligible in ammonia, insoluble in ether, slowly soluble in propylene glycol
Solubility in methanol: 238 g/L
Solubility in ethanol: 139 g/L
Vapor pressure: <2.4 kPa (20 °C)
0.1 kPa (700 °C)
Acidity (pKa): 13.9 (Na+)
Basicity (pKb): 0.0 (OH−)
Magnetic susceptibility (χ): −15.8·10−6 cm3/mol (aq.)
Refractive index (nD): 1.3576

Appearance: Clear, colorless liquid
Odor: Odorless
Physical Form: Aqueous solution
Color: Colorless

Molecular Formula (Liquid Caustic Soda): NaOH
Molecular Weight: 39.997 g/mol
Chemical Name: Sodium Hydroxide
CAS Number: 1310-73-2

Spesifications of Liquid Caustic:
Product Code: KIF-CAUL
Sodium Hydroxide %(m/m): 47.5±1.5
Sodium Chloride max. mg/kg: 250
Chloride max. mg/kg: 150

Structure of Liquid Caustic:
Crystal structure: Orthorhombic, oS8
Space group: Cmcm, No. 63
Lattice constant: 
a = 0.34013 nm, b = 1.1378 nm, c = 0.33984 nm
Formula units (Z): 4

Thermochemistry of Liquid Caustic:
Heat capacity (C): 59.5 J/(mol·K)
Std molar entropy (S⦵298): 64.4 J/(mol·K)
Std enthalpy of formation (ΔfH⦵298): −425.8 kJ/mol
Gibbs free energy (ΔfG⦵): −379.7 kJ/mol

Related compounds of Liquid Caustic:
Sodium deuteroxide
Sodium chloroxide

Other anions:
Sodium hydrosulfide
Sodium hydride
Sodium oxide

Other cations:
Lithium hydroxide
Potassium hydroxide
Rubidium hydroxide
Caesium hydroxide
Francium hydroxide

Names of Liquid Caustic:

IUPAC name:
Sodium hydroxide

Other names:
Ascarite
Caustic soda
Lye
Soda lye
Sodium hydrate
White caustic