Sodium Acetate

OVERVIEW

Sodium acetate (SO-dee-um ASS-uh-tate) is a colorless, odorless crystalline solid that often occurs as the trihydrate: NaC₂H₃O₂·3H₂O. A hydrate is a chemical compound formed when one or more molecules of water is physically added to the molecule of some other substance. Sodium acetate trihydrate has three molecules of water of hydration for every NaC₂H₃O₂ unit. Anhydrous sodium acetate readily converts to the trihydrate because it is very hygroscopic. A hygroscopic compound is one that readily absorbs moisture from the air.

HOW IT IS MADE

Sodium acetate is prepared by reacting either sodium hydroxide (NaOH) or sodium carbonate (Na₂CO₃) with acetic acid (HC₂H₃O₂). With sodium hydroxide, for example, the reaction is:

NaOH + HC₂H₃O₂ → NaC₂H₃O₂ + H₂O

KEY FACTS

FORMULA:

NaC₂H₃O₂

ELEMENTS:

Sodium, carbon, hydrogen, oxygen

COMPOUND TYPE:

Salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

82.03 g/mol

MELTING POINT:

328.2°C (622.8°F)

BOILING POINT:

Not applicable; decomposes

SOLUBILITY:

Very soluble in water; soluble in ether; slightly soluble in ethyl alcohol

The sodium acetate forms as the trihydrate, which is then recovered by evaporating the reacting solution. The anhydrous salt can be prepared by heating the hydrate to drive off the water of hydration.

COMMON USES AND POTENTIAL HAZARDS

Sodium acetate is used in a number of industries. In the textile industry, it is used as a mordant in the dyeing of fabrics and to stabilize and improve the finish of fabrics. The

Interesting Facts

• In 1995, officials in Michigan tested sodium acetate trihydrate as a deicing salt for airport runways. Experiments showed, however, that the anhydrous salt worked better than the trihydrate for this purpose.
• Sodium acetate has also been used as a deicer in parking garages. The compound is preferred to sodium chloride, widely used as a deicing compound, because sodium chloride corrodes steel rods buried in concrete and sodium acetate does not.
• Heat packs sometimes contain a solution of sodium acetate trihydrate cooled below its freezing point. When the pack is activated, the compound freezes very rapidly, releasing the heat that had been stored in its supercooled phase.

cosmetics industry uses sodium acetate as a buffering agent in a variety of personal care products. A buffering agent is a substance that maintains the acidity of a product within a certain desired range. Sodium acetate is also used by food producers for the same reason, assuring that a variety of foods have an acidity sufficient to protect the food from decaying, but not so acidic as to have an unpleasant taste. Some other applications of sodium acetate include:

• In heat packs to relieve stiffness and pain, to keep hands and feet warm, and to warm baby bottles;
• In the production of soaps, where it reacts with strong bases to reduce the harshness of the final product;
• In dialysis machines, used for people whose kidneys are not working properly, to provide the sodium ions (Na⁺) to maintain proper electrolyte balance in the body;
• As a diuretic, a drug used to promote urination;
• As an expectorant in drugs used to promote coughing to help bring up mucous;

• As a veterinary treatment for bovine ketosis, a condition caused by low blood sugar in cows that results in a wasting or weakening of the animal;
• As a buffer in the developing of photographs;
• In the tanning of hides to obtain a more even and more rapid absorption of the tanning material; and
• In the purification of glucose.

Sodium acetate is a mild irritant to the skin, eyes, and respiratory system. If inhaled, it may cause inflammation of the throat and lungs. At the level it appears in most household products, it presents a very low hazard to the average person.

Words to Know

ANHYDROUS

Lacking water of hydration.

MORDANT

A substance used in dyeing and printing that reacts chemically with both a dye and the material being dyed to help hold the dye permanently to the material.

FOR FURTHER INFORMATION

"How Do Sodium-Acetate Heat Pads Work?" How Stuff Works. http://home.howstuffworks.com/question290.htm (accessed on November 5, 2005).

"Material Safety Data Sheet: Sodium Acetate Trihydrate." Iowa State University, Department of Chemistry. http://avogadro.chem.iastate.edu/MSDS/NaOAc-3H2O.htm (accessed on November 5, 2005).

"Sodium Acetate, Anhydrous." Cornell Material Safety Data Sheets. http://msds.ehs.cornell.edu/msds/msdsdod/a73/m36008.htm#Section3 (accessed on November 5, 2005).

"Sodium Acetate Anhydrous—Physical Properties." Jarchem Industries. http://www.jarchem.com/sodium-acetate-anhydrous.htm (accessed on November 5, 2005).