Sodium Hydroxide
Sodium Hydroxide
OVERVIEW
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.
KEY FACTS
OTHER NAMES:
Caustic soda; lye; sodium hydrate; white caustic
FORMULA:
NaOH
ELEMENTS:
Sodium, oxygen, hydrogen
COMPOUND TYPE:
Base (inorganic)
STATE:
Solid
MOLECULAR WEIGHT:
40.00 g/mol
MELTING POINT:
323°C (613°F)
BOILING POINT:
1388°C (2530°F)
SOLUBILITY:
Soluble in water, ethyl alcohol, methyl alcohol, and glycerol
HOW IT IS MADE
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.
COMMON USES AND POTENTIAL HAZARDS
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.
Interesting Facts
- Solutions of sodium hydroxide are made by adding the solid compound to water, and never water to the solid. The reason is that large amounts of heat are generated when sodium hydroxide dissolves in water. That heat is absorbed by water, but would not be absorbed by solid sodium hydroxide.
- A popular food in Scandinavian countries, lutefisk, is made by soaking dried fish in sodium hydroxide until it turns into a jelly. The jelly is then soaked in water for several days to remove the poisonous lye.
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.
Words to Know
- ELECTROLYSIS
- A process in which an electric current is used to bring about chemical changes.
- HYDROLYSIS
- The process by which a compound reacts with water to form two new compounds.
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.
FOR FURTHER INFORMATION
"Determination of Acute Reference Exposure Levels for Airborne Toxicants." [Sodium Hydroxide]. Office of Environmental Health Hazard Assessment, State of California. http://www.oehha.ca.gov/air/acute_rels/pdf/1310932A.pdf (accessed on November 8, 2005).
"DOW Caustic Soda Solution." Dow Chemical Company. http://www.dow.com/causticsoda/prod/process.htm" (accessed on November 8, 2005).
"Sodium Hydroxide." International Chemical Safety Cards. http://www.cdc.gov/niosh/ipcsneng/neng0360.html (accessed on November 8, 2005).
"Sodium Hydroxide." Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/002487.htm (accessed on November 8, 2005).
White, Elaine. "Making Modern Soap with Herbs, Beeswax, and Vegetable Oils." http://www.pioneerthinking.com/soaps.html (accessed on November 8, 2005).
See AlsoChlorine; Potassium Hydroxide
Sodium Hydroxide
Sodium Hydroxide
Sodium hydroxide in household products
Industrial uses of sodium hydroxide
Sodium hydroxide, NaOH, also known as lye and caustic soda, is an extremely caustic (corrosive and damaging to human tissue) white solid that readily dissolves in water. It melts at 605°F (318°C), boils at 2,535°F (1,390°C), has a density of 2.1 g/cm3, and is soluble in water at about 111 g per 100 ml (at 20°C). In its pure form, sodium hydroxide is manufactured in flakes, granules, and pellets. Worldwide production of sodium hydroxide occurs primarily in Asia, North America, and Europe, with Europe producing about one-fourth and Asia and North American producing about one-third each. The remaining production occurs in other parts of the world.
Sodium hydroxide is used in the manufacture of soaps, rayon, and paper, in petroleum refining, and in homes as drain cleaners and oven cleaners. Sodium hydroxide is one of the strongest bases commonly used in industry. Solutions of sodium hydroxide in water are at the upper limit (most basic) of the pH scale. Sodium hydroxide is made through the process called choralkali, which uses electrolysis (passing an electric current through an aqueous solution) of sodium chloride (table salt) to produce sodium hydroxide and chlorine gas.
Sodium hydroxide in household products
Two of the more common household products containing sodium hydroxide are drain cleaners and oven cleaners. When most pipes are clogged it is with a combination of fats and grease. Cleaners that contain sodium hydroxide (either as a solid or already dissolved in water) convert the fats to soap, which dissolves in water. In addition, when sodium hydroxide dissolves in water a great deal of heat is given off. This heat helps to melt the clog. Sodium hydroxide is very damaging to human tissue (especially eyes). If a large amount of solid drain cleaner is added to a clogged drain, the heat produced can actually boil the water, leading to a splash in the eyes of a solution caustic enough to cause blindness. Some drain cleaners also contain small pieces of aluminum metal. Aluminum reacts with sodium hydroxide in water to produce hydrogen gas. The bubbles of hydrogen gas help to agitate the mixture, helping to dislodge the clog.
Oven cleaners work by converting built up grease (fats and oils) into soap, which can then be dissolved and wiped off with a wet sponge.
KEY TERMS
Base —A solution with a pH greater than seven, having a greater concentration of hydroxide ions (OH) than hydrogen ions (H+)
Caustic —Damaging to human tissue.
pH scale —A scale used to measure the acidity or alkalinity (basicity) of a substance. It ranges from 0 to 14, with pHs below seven being acidic and greater than 7 being basic (or alkaline). A pH of 7 is neutral. Substances with pHs less than 2 or greater than 12 can be caustic to human tissue.
Soluble —Capable of being dissolved. Sugar is soluble in water.
Industrial uses of sodium hydroxide
Sodium hydroxide is used to neutralize acids and as a source of sodium ions for reactions that produce other sodium compounds. In the refining of petroleum, it is used to neutralize and remove acids. The reaction of cellulose with sodium hydroxide is a key step in the manufacturing of rayon and cellophane.
Sodium hydroxide is used as a catalyst for the manufacture of biodiesel (diesel fuel made partially or wholly from vegetable oils), which has become popular to use in the 2000s. The industrial production of soaps uses sodium hydroxide in the saponification process. The food industry uses sodium hydroxide to chemically wash various foods, including fruits and vegetables, along with using it to process cocoa, soft drinks, and ice cream.
Resources
BOOKS
Emsley, John. Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford, UK: Oxford University Press, 2003.
Lide, David R., ed. CRC Handbook of Chemistry and Physics Boca Raton, FL: CRC Press, 2005.
Siekierski, Slawomir. Concise Chemistry of the Elements. Chichester, UK: Horwood Publishing, 2002.
Snyder, C.H. The Extraordinary Chemistry of Ordinary Things. 4th ed. New York: John Wiley and Sons, 2002.
Louis Gotlib
Sodium Hydroxide
Sodium hydroxide
Sodium hydroxide, NaOH, also known as lye or caustic soda, is an extremely caustic (corrosive and damaging to human tissue ) white solid that readily dissolves in water . Sodium hydroxide is used in the manufacture of soaps, rayon, and paper , in petroleum refining, and in homes as drain cleaners and oven cleaners. Sodium hydroxide is one of the strongest bases commonly used in industry. Solutions of sodium hydroxide in water are at the upper limit (most basic) of the pH scale. Sodium hydroxide is made by the electrolysis (passing an electric current through a solution ) of solutions of sodium chloride (table salt ) to produce sodium hydroxide and chlorine gas.
Sodium hydroxide in household products
Two of the more common household products containing sodium hydroxide are drain cleaners and oven cleaners. When most pipes are clogged it is with a combination of fats and grease. Cleaners that contain sodium hydroxide (either as a solid or already dissolved in water) convert the fats to soap , which dissolves in water. In addition, when sodium hydroxide dissolves in water a great deal of heat is given off. This heat helps to melt the clog. Sodium hydroxide is very damaging to human tissue (especially eyes). If a large amount of solid drain cleaner is added to a clogged drain, the heat produced can actually boil the water, leading to a splash in the eyes of a solution caustic enough to cause blindness. Some drain cleaners also contain small pieces of aluminum metal . Aluminum reacts with sodium hydroxide in water to produce hydrogen gas. The bubbles of hydrogen gas help to agitate the mixture, helping to dislodge the clog.
Oven cleaners work by converting built up grease (fats and oils) into soap, which can then be dissolved and wiped off with a wet sponge.
Industrial uses of sodium hydroxide
Sodium hydroxide is used to neutralize acids and as a source of sodium ions for reactions that produce other sodium compounds. In petroleum refining it is used to neutralize and remove acids. The reaction of cellulose with sodium hydroxide is a key step in the manufacturing of rayon and cellophane.
Resources
periodicals
"Corticosteroids Can't Counter Caustics," Science News vol. 138, p. 174, Sept. 15, 1990. "How Lye is Made and Some Uses," Countryside and Small Stock Journal Vol. 78, p. 37, March-April 1994.
Louis Gotlib
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Base
—A solution with a pH greater than seven, having a greater concentration of hydroxide ions (OH) than hydrogen ions (H+)
- Caustic
—Damaging to human tissue.
- pH scale
—A scale used to measure the acidity or alkalinity (basicity) of a substance. It ranges from 0 to 14, with pH's below seven being acidic and greater than 7 being basic (or alkaline). A pH of 7 is neutral. pH's less than 2 or greater than 12 can be caustic to human tissue.
- Soluble
—Capable of being dissolved. Sugar is soluble in water.