Sodium Carbonate
Overview
Sodium carbonate (SO-dee-um KAR-bun-ate) is an odorless white powder or crystalline solid with an alkaline taste. (Baking soda is another substance with an alkaline taste.) It is hygroscopic, meaning that it has a tendency to absorb moisture from the air. It also exists as the monohydrate (Na2CO3·H2O) and as the decahydrate (Na2CO3·10H2O), each with slightly different physical properties from those of the anhydrous salt. The anhydrous form of sodium carbonate is commonly known as soda ash, while the decahydrate is often called sal soda or washing soda. Sodium carbonate has long been one of the most important chemical compounds produced in the United States. Its primary use is in the manufacture of glass and other chemicals.
Key Facts
Other Names:
Anhydrous salt: soda ash; Solvay soda; decahydrate: sal soda; washing soda (see Overview)
Formula:
Na2CO3
Elements:
Sodium, carbon, oxygen
Compound Type:
Salt (inorganic)
State:
Solid
Molecular Weight:
105.99 g/mol
Melting Point:
858.1°C (1576°F)
Boiling Point:
Not applicable; begins to decompose below melting point
Solubility:
Soluble in water; insoluble in ethyl alcohol
How It Is Made
Humans have known about and used sodium carbonate for thousands of years. The ancient Egyptians extracted the compound from a mineral known as natron found in dry lake bottoms. Natron is a combination of sodium carbonate and sodium bicarbonate. The Egyptians used sodium carbonate in the mummification of dead bodies. The compound dried out the bodies of the dead and prevented them from decaying. The technique was so effective that some mummified bodies over 3,000 years old are in as good a condition today as they were when the person died. Over the centuries, sodium carbonate was also produced by the combustion of organic matter, especially seaweed. This method of production accounts for the compound's common name of soda ash (ash containing sodium compounds).
The burning of dead plants does not produce very large quantities of sodium carbonate, so early chemists searched for synthetic methods of producing the increasingly important compound. The first breakthrough in that search occurred in 1791 when French chemist Nicolas Leblanc (1742–1806) invented a method for making sodium carbonate that became the industry standard for nearly a century. In the Leblanc method, sodium chloride (NaCl) is treated with sulfuric acid (H2SO4) to make sodium sulfate (Na2SO4) and hydrochloric acid (HCl). The sodium sulfate is then heated with charcoal (nearly pure carbon) and limestone (CaCO3). The product of this reaction is a dark ashy material that contains sodium carbonate, calcium sulfide, carbon dioxide, and other byproducts:
Na2SO4 + 2C + CaCO3 → Na2CO3 + CaS + 2CO2
The sodium carbonate is extracted from this mixture and purified. The Leblanc invention was one of the great breakthroughs in the early years of chemical science. It made possible, among other things, the mass production of soap for the first time in human history.
As important as Leblanc's invention was, it suffered from one serious drawback: It required large amounts of energy. For this reason, chemists were always on the lookout for an alternative method for producing sodium carbonate that was less energy-intensive. That breakthrough came in 1861 when Belgian chemist Ernest Solvay (1838–1922) found a new way to make the important compound. Solvay found that treating sodium chloride with carbon dioxide and ammonia resulted in the formation of sodium bicarbonate and ammonium bicarbonate. Simply heating the sodium bicarbonate converts the bicarbonate to the carbonate. Like Leblanc's discovery, the Solvay process is regarded as one of the great accomplishments in the first century of industrial chemistry. By 1900, almost all of the sodium carbonate produced in the world was being made by the Solvay process.
That situation has changed. Today the most important source of sodium carbonate is natural minerals, such as thermonatrite (sodium carbonate monohydrate; Na2CO3·H2O) or natron (or natrite; sodium carbonate decahydrate; Na2CO3·10H2O). These minerals are obtained from rocky deposits or from brines that are rich in the compound. Brine is water that is saturated with salts, such as sodium chloride, potassium chloride, and sodium carbonate. It is similar to, but saltier than, seawater.
Common Uses and Potential Hazards
About half of all the sodium carbonate produced in the United States is used to make glass products such as glass containers, flat glass, and fiber insulation. Glass is made by fusing (melting) a mixture of silica (silicon dioxide; SiO2), sodium carbonate, limestone (calcium carbonate; CaCO3), and other materials. The recipe differs considerably depending on the type of glass one wishes to make. For example, oxides of various metals such as iron(III) oxide and copper(II) oxide are added to provide a reddish tint to the glass.
The second highest use of sodium carbonate is in the production of other chemical compounds, followed by the compound's use in the production of soaps and detergents. Other applications of the compound include:
- The production of pulp and paper products;
- The removal of sulfur dioxide from flu gases in factories;
- In water purification and waste water treatment facilities;
- As a mordant in the dyeing of cloth;
- In the refining of petroleum;
- As a catalyst in the process by which coal is converted into a liquid fuel;
- For the bleaching of cotton and linen fabrics;
- As an emetic (a compound that induces vomiting); and
- In cosmetics and personal care products because of its ability to clean skin and help clear up rashes.
Interesting Facts
- Over the last decade, consumption of sodium carbonate in the United States has been decreasing, largely because glass containers (made with sodium carbonate) are being replaced by plastic containers. However, the industry has not gone into decline primarily because the demand for glass in developing countries continues to increase at a rate that matches the decline in glass bottle demand in the United States.
No serious health hazards have been associated with the use of sodium carbonate in any of its forms.
Words to Know
Lacking water of hydration. A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure. 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. A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants. Water that has combined with a compound by some physical means.For Further Information
Kiefer, David M. "Soda Ash, Solvay Style." Today's Chemist (February 2002): 87-88+. Also available online at http://pubs.acs.org/subscribe/journals/tcaw/11/i02/html/02chemchron.html (accessed on November 8, 2005).
Lister, Ted, compiler. "Sodium Carbonate—A Versatile Material." Royal Society of Chemistry. http://www.chemsoc.org/pdf/LearnNet/rsc/SodiumCarb_sel.pdf (accessed on November 8, 2005).
Monet, Jefferson. "An Overview of Mummification in Ancient Egypt." TourEgypt.net. http://www.touregypt.net/featurestories/mummification.htm (accessed on November 8, 2005).
"Soda Ash or Trona." Mineral Information Institute. http://www.mii.org/Minerals/phototrona.html (accessed on November 8, 2005).
"Sodium Carbonate." United Nations Environmental Programme. http://www.inchem.org/documents/sids/sids/Naco.pdf (accessed on November 8, 2005).
See Also
Sodium Bicarbonate
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