Sodium hydroxide

Sodium hydroxide (drain cleaner. Worldwide production in 1998 was around 45 million tonnes. Sodium hydroxide is the most used base in chemical laboratories.

Pure sodium hydroxide is a white solid; available in pellets, flakes, granules and as a 50% saturated solution. It is solution will leave a yellow stain on fabric and paper.

Chemical properties

Sodium hydroxide is completely sodium chloride is formed:

NaOH(aq) + l)

In general such neutralization reactions are represented by one simple net ionic equation:

H₃O⁺(aq) → 2H₂O

This type of reaction with a strong acid, releases heat, and hence is referred to as titrations, which is a common method to determine the concentration of acids. Another type of reaction that sodium hydroxide is involved in is with acidic oxides. The reaction of sulfur dioxide (SO₂) also react completely. Such reactions are often used to "scrub" harmful acidic gases (like SO₂ and H₂S) and prevent their release into the atmosphere.

2NaOH + Na₂CO₃ + H₂O

Sodium hydroxide slowly reacts with glass to form titanium are attacked rapidly. In 1986 an aluminium road tanker in the UK was mistakenly used to transport 25% sodium hydroxide solution, causing pressurisation of the contents and damage to the tanker. For this reason aluminium pans should never be cleaned with sodium hydroxide.

2Al(g) + 2Na₃AlO₃(aq)

Many non-metals also react with sodium hydroxide, giving salts. For example sodium silicate.

Unlike NaOH, the hydroxides of most metals are insoluble, and therefore sodium hydroxide can be used to precipitate metal hydroxides. One such hydroxide is aluminium sulfate by reacting with NaOH:

6NaOH(aq) + Na₂SO₄(aq)

Sodium hydroxide reacts readily with soluble KOH is often preferred.

Manufacture

In 1998, total world production was around 45 million tonnes. North America and Asia collectively contributed around 14 million tonnes, while Europe produced around 10 million tonnes.

Methods of production

Sodium hydroxide is produced (along with hydroxide ion:

2Na⁺ + 2H₂O + 2e⁻ → H₂ + 2NaOH

To produce NaOH it is necessary to prevent reaction of the NaOH with the chlorine. This is typically done in one of three ways, of which the membrane cell process is economically the most viable.

• Mercury cell process (also called the cathode; this sodium is then reacted with water to produce NaOH. There have been concerns about mercury releases, although modern plants claim to be safe in this regard.^[1]
• Diaphragm cell process – uses a steel cathode, and the reaction of NaOH with Cl₂ is prevented using a porous diaphragm, often made of asbestos fibers. In the diaphragm cell process the anode area is separated from the cathode area by a permeable diaphragm. The brine is introduced into the anode compartment and flows through the diaphragm into the cathode compartment. A diluted caustic brine leaves the cell. The caustic soda 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 caustic soda. 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.^[2][3]
• Membrane cell process – similar to the diaphragm cell process, with a Nafion membrane to separate the cathode and anode reactions. Only sodium ions and a little water pass through the membrane. It produces a higher quality of NaOH. Of the three processes, the membrane cell process requires the lowest consumption of electric energy and the amount of steam needed for concentration of the caustic is relatively small (less than one tonne per tonne of caustic soda).^[4][5]

An older method for sodium hydroxide production was the carbon dioxide and sodium oxide. This method is still occasionally used. It helped establish sodium hydroxide as an important commodity chemical.

The LeBlanc process was superseded by the Solvay process in the late 19th century.

Major producers

In the United States, the major producer of sodium hydroxide is the chloralkali process^[6].

Uses

General applications

Sodium hydroxide is the principal strong neutralization of acidic materials. It can be used also as a neutralizing agent in petroleum refining

Gold pennies

Sodium hydroxide has also been used in conjunction with brass.

Alumina production - Bayer process

Sodium hydroxide is used in the refining of smelting process.

Use in chemical analysis

In Biuret test.

Soap production

Sodium hydroxide was traditionally used in soap making (cold process soap, saponification). The Arabs began producing soap in this way in the 7th century, and the same basic process is used today.

Paper making

Sodium hydroxide was also widely used in making paper. Along with sodium sulfide, NaOH is a key component of the white liquor solution used to separate lignin from oxidative extraction, and simple extraction, all of which require a strong alkaline environment with a pH > 10.5 at the end of the stages.

Biodiesel

For the manufacture of biodiesel, sodium hydroxide is used as a methanol. It is used more often than potassium hydroxide because it is cheaper and a smaller quantity is needed.

Aluminium etching

Strong bases attack aluminium. This can be useful in etching through a resist or in converting a polished surface to a satin-like finish, but without further anodizing or allodizing the surface may become corroded, either under normal use or in severe atmospheric conditions.

Food preparation

Food uses of lye include washing or chemical peeling of fruits and vegetables, chocolate and sodium carbonate is often used in place of sodium hydroxide^[7].

Specific foods processed with lye include:

• The Scandinavian delicacy known as lutefisk (from lutfisk, "lye fish").
• Hominy is dried calcium hydroxide instead of sodium hydroxide.
• Sodium hydroxide is also the chemical that causes gelling of egg whites in the production of Century eggs.
• German pretzels are poached in a boiling sodium hydroxide solution before baking, which contributes to their unique crust.

Delignification of Cellulosic Materials

Sodium Hydroxide, in addition

Domestic uses

Sodium hydroxide is used in the home as a drain cleaning agent for clearing clogged drains. It is distributed as a dry crystal or as a thick liquid gel. The chemical mechanism employed is the conversion of grease to a form of acidic versions) are highly caustic and should be handled with care.

Lye has been used as a relaxer to straighten hair. However, because of the high incidence and intensity of chemical burns, chemical relaxer manufacturers have now switched to other alkaline chemicals, although lye relaxers are still available, used mostly by professionals.

Tissue Digestion

This is a process that was used with farm animals at one time. This process involves the placing of a carcass into a sealed chamber, which then puts the carcass in a mixture of lye and water, which breaks chemical bonds keeping the body intact. This eventually turns the body into a coffee-like liquid, and the only solid remains are bone hulls, which could be crushed between one's fingertips. It is also of note that sodium hydroxide is frequently used in the process of decomposing roadkill dumped in landfills by animal disposal contractors^{[citation needed]}.

Sodium hydroxide has also been used by criminals and serial killers to dispose of their victims' bodies.^{[citation needed]}

Illegal drugs

Sodium hydroxide is a key reagent in the process of making Methamphetamine and other illegal drugs. Contrary to popular media reports, it is not actually an "ingredient" in these drugs, but simply a strong base used to manipulate the pH at various points in a chemical synthesis.

Sodium Hydroxide is also used for DMT extraction from various psychoactive plants.

It can also be used to convert GHB.

Safety

Solid sodium hydroxide or solutions containing high concentrations of sodium hydroxide may cause chemical burns, permanent injury or scarring, and blindness.

Dissolution of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables.

The combination of aluminium and sodium hydroxide results in a large production of hydrogen gas:
2Al(g) + 2Na₃AlO₃(aq).
Mixing these two in a closed container is therefore dangerous.

See also

• Common chemicals
• Soda lime

References

General references

1. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
2. Heaton, A. (1996) An Introduction to Industrial Chemistry, 3rd edition, New York:Blackie. ISBN 0-7514-0272-9.
3. Kirk-Othmer Encyclopedia of Chemical Technology 5th edition (online, account needed), John Wiley & Sons. Accessed November 21, 2005.
4. Euro Chlor - How is chlorine made? Chlorine Online