Sodium Carbonate
Sodium carbonate is a chemical compound which conforms to the general formula Na2CO3.
It is commonly referred to as soda ash because it was originally obtained from the ashes of burnt sea weeds. Now, soda ash is primarily manufactured by a method known as the Solvay process. Currently, it is one of the top industrial chemicals, in terms of volume, produced in the United States. It is mostly used in the manufacture of glass, but is also used in the manufacture of other products and is an important precursor to many of the sodium compounds used throughout industry.
The process for obtaining sodium carbonate has changed significantly over time. It was originally produced by burning seaweeds that were rich in sodium. When the weeds were burned, sodium would be left in the ashes in the form of sodium carbonate (Na2SO4 + CaCO3 CaSO4 + Na2CO3). Although this process was effective, it could not be used to produce large amounts.
The first process that allowed production of significant amounts of sodium carbonate was a synthetic process known as the LeBlanc process, developed by the French chemist Nicolas LeBlanc (1742-1806). In this process, salt reacts with sulfuric acid to produce sodium sulfate and hydrochloric acid (NaCl + H2SO4 Na2SO4 + HCl). The sodium sulfate was heated in the presence of limestone and coal and the resulting mixture contained calcium sulfate and sodium carbonate, which was then extracted.
Two significant problems with the LeBlanc process, including high expense and significant pollution, inspired a Belgian chemical engineer named Ernest Solvay (1838-1922) to develop a better process for creating sodium carbonate. In the Solvay process, ammonia and carbon dioxide are used to produce sodium carbonate from salt and limestone. Initially, the ammonia and carbon dioxide reacts with water to form the weak electrolytes, ammonium hydroxide and carbonic acid. These ions react further and form sodium bicarbonate. Since the bicarbonate barely dissolves in water, it separates out from the solution. At this point, the sodium bicarbonate is filtered and converted into sodium carbonate by heating.
Synthetic production is not the only method of obtaining sodium carbonate. A significant amount is mined directly from naturally occurring sources. The largest natural sources for sodium carbonate in the United States, are found around Green River, Wyoming and in the dried-up desert lake Searles in California.
At room temperature, sodium carbonate (Na2CO3) is an odorless, grayish-white powder which is hygroscopic. This means when it is exposed to air, it can spontaneously absorb water molecules. Another familiar compound that has this hygroscopic quality is sugar. Sodium carbonate has a melting point of 1,564o F (851o C), a density of 2.53 g/cm3, and is soluble in water. A water solution of soda ash has a basic pH and a strong alkaline taste. When it is placed in a slightly acidic solution, it decomposes and forms bubbles. This effect, called effervescence, is found in many commercial antacid products which use sodium carbonate as an active ingredient.
Anhydrous (without water) sodium carbonate can absorb various amounts of water and form hydrates that have slightly different characteristics. When one water molecule per molecule of sodium carbonate is absorbed, the resulting substance, sodium carbonate monohydrate, is represented by the chemical formula Na2CO3HOH. This compound has a slightly lower density than the anhydrous version. Another common hydrate is formed by the absorption of 10 water molecules per molecule of sodium carbonate. This compound, Na2CO310HOH known as sodium carbonate decahydrate, exists as transparent crystals that readily effervesce when exposed to air.
Sodium carbonate is utilized by many industries during the manufacture of different products. The most significant user is the glass industry, which uses sodium carbonate to decompose silicates for glass making. The cosmetic industry uses it while manufacturing soap. The chemical industry uses it as a precursor to numerous sodium containing reagents. It is also important in photography, the textile industry, and water treatment. In addition to these industrial applications, sodium carbonate is used in medicine as an antacid.
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