Sodium hydroxide (SO-dee-um hye-DROK-side) is a white
deliquescent solid commercially available as sticks, pellets,
lumps, chips, or flakes. A deliquescent material is one that
absorbs moisture from the air. Sodium hydroxide also reacts
readily with carbon dioxide in the air to form sodium carbonate.
Sodium hydroxide is the most important commercial caustic. A
caustic material is a strongly basic or alkaline material that
irritates or corrodes living tissue. The compound ranked number
11 among chemicals produced in the United States in 2004.
Sodium hydroxide is produced commercially simultaneously
with chlorine gas by the electrolysis of a sodium
chloride solution. In this process, an electric current breaks
down sodium chloride into its component elements, sodium
and chlorine. The chlorine escapes as a gas, while the sodium
metal form reacts with water to form sodium hydroxide
2NaCl ! 2Na + Cl2
2Na + 2H2O ! 2NaOH + H2
Sodium hydroxide can also be produced easily by means
of other chemical reactions. For example, the reaction
between slaked lime (calcium hydroxide; Ca(OH)2) and soda
ash (sodium carbonate; Na2CO3) produces sodium hydroxide:
Ca(OH)2 + Na2CO3 ! 2NaOH + CaCO3
None of these alternative methods can compete economically,
however, with the preparation by electrolysis.
Sodium hydroxide has a great variety of household and
industrial uses. It is the active ingredient in drain cleaners
such as Drano because it breaks up and dissolves the greasy
mass that is responsible for drain blockages. It is also an
ingredient in many other household products, including oven
cleaners, metal polishes, and hair straighteners. Sodium
hydroxide is also used in the preparation of homemade and
processed foods. It is used in the preparation of soft drinks,
chocolate, ice creams, caramel coloring, and cocoa. Hominy, a
starchy food similar to grits, is made by soaking corn kernels
in a solution of sodium hydroxide in water. Bakers glaze
pretzels and German lye rolls with a weak lye solution before
baking them. The lye gives baked goods a crisp crust. Some
people use lye to cure olives.
The largest single use for sodium hydroxide is in the
production of organic compounds from which polymers are
made, such as propylene oxide and the ethylene amines, and
of the polymers themselves, including the polycarbonates
and epoxy resins. About a third of all the sodium hydroxide
produced in the United States goes to this application.
Another important use of sodium hydroxide is in the pulp
and paper industry, where it is used to digest (break down)
the raw materials from which pulp and paper are made.
About 13 percent of all the sodium hydroxide made in the
United States goes to this application. Sodium hydroxide is
also an important raw material in the manufacture of soap.
The method by which soap is made has not changed very
much for thousands of years. A fat or oil is added to a boiling
solution of sodium hydroxide in water. The fat or oil hydrolyzes
into its component parts, glycerol and fatty acids. The
sodium hydroxide then reacts with the fatty acids, forming
sodium salts. The sodium salt of a fatty acid is a soap. Sodium
hydroxide is also an important raw material in the manufacture
of inorganic compounds, especially sodium and calcium
hypochlorite, sodium cyanide, and a number of sulfur-containing
compounds. Some other important uses of sodium
hydroxide include:
• In the manufacture of cellophane and rayon;
• As a neutralizing agent during the refining of petroleum;
• In the manufacture of aluminum metal;
• For the refining of vegetable oils;
• As an agent for peeling fruits and vegetables for processing;
• In the extraction of metals from their ores;
• For the processing of textiles;
• In water treatment facilities;
• For etching and electroplating operations; and
• In a wide variety of research laboratory applications.
Sodium hydroxide is one of the most caustic substances
known and a strong irritant to the skin, eyes, and respiratory
system. Exposure to sodium hydroxide dust, powder, or solid
can cause burning of the skin and eyes, with possible permanent
damage to one’s vision. Ingestion of the compound
causes burning of the mouth, esophagus, and stomach, resulting
in nausea, diarrhea, internal bleeding, scarring, and permanent
damage to the lungs and gastrointestinal system.
More serious results, such as a drop in blood pressure and
collapse, are also possible.
