Sodium Carbonate, more commonly known as soda ash, is one of the most widely used compounds in the United States. The importance of sodium carbonate can be clearly seen by the Federal Reserve Board’s incorporation of monthly soda ash production into monthly economic indicators used to monitor the U.S. economy (1). This “cornerstone” salt has been available in relative abundance for millennia. The first use of soda ash has been accredited to the ancient Egyptians. They were able to obtain soda ash from dry lake bed deposits or by burning seaweed and other aquatic plants. The extraction of soda ash from various plants continued until the middle of the 19^th century. The name “soda ash” originates from the ancient methods of extraction. “Soda” refers to the plants that grow in salt marshes. “Ash” simply refers to the burning of the plants.

Naturally soda ash can be obtained by the collecting, drying, and subsequent burning of salt-tolerant plants known as halophytes. The ashes of these halophytes are then “lixiviated”, or washed with water, to create the alkali solution (2). The solution is then boiled dry to create the final product. This method, used until the middle 1800s, ultimately does not produce a very pure product. The concentration of soda ash varied depending on several factors, including plant species and geographic location. Sodium Carbonate can also be found in the form of Trona (trisodium hydrogendicarbonate dehydrate or Na₃HCO₃CO₃·2H₂O) deposits. In the United States these deposits can be mined in California, Wyoming, and Utah. These deposits come in colorless or white crystal structures that ranks at 2.5 on the Mohs scale. The crystal structure is monoclinic and consists of units of 3 edge-sharing sodium polyhedral, cross-linked by carbonate groups and hydrogen bonds (3).

By the end of the 18^th century methods of producing sodium carbonate were simply not sufficient to keep up with the demand in Europe (4). In 1775 the French Academy of Sciences offered a prize for anyone who could synthesize soda ash from salt (5). In 1791 Nicolas Leblanc was able to come up with an effective method to produce soda ash and in the first year he was able to produce over 320 tons per year. Although he answered the call of the French Academy of Science and was successful, he was denied his prize money because of the French Revolution. The Leblanc process is a batch process which starts with sodium chloride, subjects it to various reactions, and ends with sodium carbonate. The process begins with the heating of a sodium chloride/sulfuric acid solution to produce sodium sulfate and hydrogen chloride gas. This reaction occurs by the following chemical equation:

2 NaCl + H₂SO₄ → Na₂SO₄ + 2 HCl

This reaction was originally discovered by Carl Scheele in 1772. However, the reason this process is referred to as the Leblanc process and not the Scheele process is because Leblanc was able to solve the mystery of the reactions to form the end product of sodium carbonate. The second step in the Leblanc process was mixing the sodium sulfate “salt cakes” with crushed limestone (calcium carbonate) and coal and firing the mixture (5). This reaction ultimately occurs in two steps: in the first, the coal is oxidized into carbon dioxide which reacts with the sodium sulfate and reduces it to sulfide; the second step occurs as the calcium and sodium swap their ligands to make a more thermodynamically favorable combination of sodium carbonate and calcium sulfide (5). This mixture is often referred to as “black ash”. These two reactions can be expressed by the following chemical equations:

Na₂SO₄ + 2 C → Na₂S + 2 CO₂       (Reduction of sulfate)

Na₂S + CaCO₃ → Na₂CO₃ + CaS     (Thermodynamically favorable recombination)

The black ash was then washed with water. The water wash was evaporated to yield sodium carbonate. The extraction portion of the Leblanc process was termed lixiviation (5). The downside of the Leblanc process is the cost of the reagents and the harsh byproducts, namely hydrogen chloride gas. In 1811 Augustin Jean Fresnel discovered that sodium bicarbonate precipitates when carbon dioxide is bubbled through ammonia-containing brine (6). Although this reaction ultimately became key to what is now called the Solvay process, Fresnel did not publish his findings. In 1861, a Belgian chemist by the name of Ernest Solvay turned his attention the creating a cleaner, cheaper method of producing sodium carbonate. Solvay’s solution was to use an 80-foot tall gas absorption chamber in which carbon dioxide bubbled through a descending flow of brine, together with an efficient method of recovering and recycling ammonia. The net reaction of the Solvay process is expressed by:

2 NaCl + CaCO₃ → Na₂CO₃ + CaCl₂

However, the individual steps of the reaction are rather complex. The first step of the process consists of bubbling ammonia (NH₃) through a brine solution. The second step takes the ammoniated brine solution and bubbles in carbon dioxide (CO₂), which causes sodium bicarbonate (Na₂HCO₃) to precipitate. These steps can be summarized by the following:

NaCl + CO₂ + NH₃ + H₂O → NaHCO₃ + NH₄Cl

The sodium bicarbonate is then filtered from the ammonium chloride (NH₄Cl) solution and is reacted with quicklime (calcium oxide (CaO)).

2 NH₄Cl + CaO → 2 NH₃ + CaCl₂ + H₂O

Sodium carbonate (Na₂CO₃) is formed through calcination of the previous products:

2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂

This process is considered to be relatively efficient because a very small amount of ammonia is needed because it is regularly recycled after each reaction. One major byproduct of the Solvay process is calcium chloride, which is usually used as road salt (6). A majority of the world’s soda ash supply is made using the Solvay process.

Sodium carbonate has a chemical formula of Na₂CO₃, a molecular weight of 105.988 g/mol and a density of 2.5 g/cm³. Pure soda ash is a grayish-white, odorless powder. It has a melting point of 856ºC and no boiling point because it begins to decompose before it boils. Sodium carbonate is insoluble in ethanol and is soluble up to 30g/100mL H₂O at 20ºC. Spectral analysis yielded an index of refraction of 1.535 (7).

Soda ash has developed numerous applications over the years. The majority of soda ash produced in the world is used in the manufacture of glass. In this process the sodium carbonate acts as a flux for silica, thereby lowering the melting point of the mixture to reasonable temperature. Sodium carbonate can also act as a relative strong base: it is often used as a pH regulator for the action of a majority of film developing agents, in pools it is regularly used to neutralize the corrosive effects of added chlorine and to raise the overall pH of the water, in taxidermy it is added to water to remove flesh from bone, in chemistry it is used as a primary standard for acid-base titrations because it is solid at room temperature and air-stable (making it easy to weigh), and it is used as a water softener for laundry (2). Sodium carbonate also plays an important role in maintaining the homeostasis of acid-base reactions in biological systems, most importantly blood pH.

The strategic importance of sodium carbonate is questionable. While it can be used in the manufacture of glass, as a cleaning agent, etc., soda ash is in no way considered to be rare. Sodium Carbonate can be made through the Solvay process and found in large deposits around the world. When the scarcity of a substance is nonexistent, the strategic importance of the substance drops drastically, and such is the case with sodium carbonate. Soda ash can currently be bought for anywhere between $289.00 and $354.00 per ton depending on the desired quantity (8).

Sodium carbonate is a relatively safe material according to its MSDS sheet. Sodium carbonate is a skin and eye irritant and can also be hazardous if ingested or inhaled (9). It is non-flammable, but does emit Na₂O fumes when heated to decomposition. Sodium carbonate can ignite and burn intensely when it comes into contact with fluoride. It can also reacts explosively when it comes into contact with re-hot aluminum metal. It is recommended to wear gloves, a lab coat, dust respirator, and slash googles when handling sodium carbonate.

From a realistic standpoint, sodium carbonate is used mostly for glass production. From a chemical perspective, the chemical equation that summarizes the creation of glass is:

 

 

 

In this reaction, sodium carbonate is reacted with silica sand (SiO₂) at about 1500ºC to produce sodium silicate (Na₂SiO₃) and carbon dioxide (CO₂) (10). When the glass is molten, different elements and compounds can be added to change the color. For example the addition of nickel to the molten glass can result in blue, violet, or even black glass (11). Sodium carbonate can be analyzed in solution using a GC mass spectrophotometer to give mass spectra and a look into the purity of the sample. Soda ash can also be analyzed using an IR spectrophotometer, which may give insight into the different pieces of the molecular structure.

The United States is currently the world’s largest producer of sodium carbonate with more than 11.5 million metric tons produced in 2013 (12). The lion’s share of the soda ash produce is actually mined out of deposits in California, Wyoming, and Utah; a stark contrast from the necessity of the Solvay process in Europe. Due to the abundance of soda ash, whether it be made through the Solvay process or harvested from deposits, it has not really had an effect on society or culture. While it is essential in the process of glass making, it cannot be considered rare or valuable, which generally leads to an absence of public interest. Sodium carbonate is used for a number of purposes in today’s society which allows it to remain a useful compound, but nothing that should be coveted for its value. Sodium carbonate simply lacks the characteristics needed to be considered powerful enough to change the world.

 

References

(1). http://www.ansac.com/products/about-soda-ash/ , accessed 6 February 2015.

(2). http://en.wikipedia.org/wiki/Sodium_carbonate , accessed 6 Feb, 2015.

(3). http://en.wikipedia.org/wiki/Trona , accessed 6 Feb, 2015.

(4). https://www.academia.edu/8035384/Soda_Ash_Production , accessed 6 Feb, 2015.

(5). http://en.wikipedia.org/wiki/Leblanc_process , accessed 6 Feb, 2015.

(6). http://en.wikipedia.org/wiki/Solvay_process , accessed 8 Feb, 2015.

(7). http://pubchem.ncbi.nlm.nih.gov/compound/sodium_carbonate# , accessed 8 Feb, 2015.

(8). http://www.solvaychemicals.us/EN/Products/sodiumproducts/sodaash.aspx , accessed 15 Feb, 2015.

(9). http://www.sciencelab.com/msds.php?msdsId=9927263 , accessed 15 Feb, 2015.

(10). http://www.pilkington.com/pilkington-information/about+pilkington/education/chemistry+of+glass.htm , accessed 16 Feb, 2015.

(11). http://en.wikipedia.org/wiki/Glass_coloring_and_color_marking , accessed 16 Feb, 2015.

(12). http://minerals.usgs.gov/minerals/pubs/commodity/soda_ash/myb1-2013-sodaa.pdf , accessed 16 Feb, 2015.