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
A process in which an electric current is used to bring about chemical changes. 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 Also
Chlorine; Potassium Hydroxide
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