The sodium carbonate (Na 2 CO 3) is an inorganic salt of sodium, alkali metal and carbonic acid. It is also known worldwide as soda ash. The lakes and the volcanic activities enriched the soils with sodium, from which the plants were nourished; then, after a fire, these plants spread the carbonate ashes.
How does this salt arise from metallic sodium? Pure sodium has a 3s 1 valence configuration. The electron of the 3s 1 orbital is easily detached by other elements of nature (such as sulfur, oxygen, chlorine, fluorine, etc.), forming mineral compounds in which the stable ion Na + participates.
Na + is accompanied by other ionic species in these solids; Of these, sodium carbonate is just one more present in nature. Since then it has been used in all civilizations throughout the ages. These civilizations were finding in this grayish white powder beneficial properties for their homes and their people.
These properties marked its uses, which today maintain traditional aspects of the past, and others adapt to current needs.
Sodium carbonate is very abundant in nature, and perhaps also in other territories outside planet Earth, such as some of the moons of the solar system.
Formula
The chemical formula for sodium carbonate is Na 2 CO 3. How is it interpreted? It means that, in the crystalline solid, for every CO 3 2– ion there are two Na + ions.
Structure
The upper image shows the structure of Na 2 CO 3 anhydride (also called calcined soda). The purple spheres correspond to Na + ions, while the black and red spheres correspond to CO 3 2– ions.
Carbonate ions have a flat trigonal structure, with oxygen atoms at their vertices.
The image provides a panorama seen from a higher plane. The Na + ions are surrounded by six oxygen atoms, coming from the CO 3 2– ions. That is, in Na 2 CO 3 anhydride sodium meets an octahedral coordination geometry (it is enclosed in the center of an octahedron).
However, this structure is also capable of accommodating water molecules, interacting by hydrogen bonds with the vertices of the triangles.
In fact, the hydrates of Na 2 CO 3 (Na 2 CO 3 · 10H 2 O, Na 2 CO 3 · 7H 2 O, Na 2 CO 3 · H 2 O, and others) are of greater abundance than the anhydrous salt.
Thermonatrite (Na 2 CO 3 · H 2 O), natron (Na 2 CO 3 · 10H 2 O) and trone (Na 3 (HCO 3) (CO 3) · 2H 2 O are the main natural sources of carbonate sodium, especially the mineral trona, represented in the first image.
Applications
Sodium carbonate fulfills numerous functions in people, homes and industry, among these functions the following stand out:
- Sodium carbonate is used in many cleaning products. This is due to its disinfectant capacity, its power to dissolve fats and its property to soften water. It is part of detergents used in laundries, automatic dishwashers, glass cleaners, stain removers, bleaches, etc.
- Carbonate disinfectant can be used on non-rough hard surfaces, such as floors, walls, porcelain and bathtubs, with the exception of fiberglass and aluminum, which can be scratched by it.
- It is used in some foods to avoid caking that can occur in these.
- It is present in various personal care products, such as bubble baths, toothpastes and soaps.
- It is used in the glass industry due to its ability to decompose silicates.
- It is used in the maintenance of swimming pools, where it performs a disinfectant and pH regulating function.
- In humans it is used therapeutically in the treatment of heartburn and dermatitis.
- In veterinary medicine it is used in the treatment of ringworm and cleaning the skin.
How is it done?
Sodium carbonate can be manufactured using brine from the seas and limestone (CaCO 3) in the Solvay process. In the image above a diagram of the process is illustrated indicating the production routes, as well as the reagents, intermediaries and products. The reagents are written with green letters, and the products with red letters.
Tracking these reactions can get a bit tricky, but the overall equation that indicates only the reactants and products is:
2NaCl (aq) + CaCO 3 (s) <=> Na 2 CO 3 (s) + CaCl 2 (aq)
CaCO 3 has a very stable crystalline structure, so it constantly demands a lot of energy to decompose it into CO 2. In addition, this process generates large amounts of CaCl 2 (calcium chloride) and other impurities, whose discharges affect the quality of the waters and the environment.
There are also other production methods for sodium carbonate in industrial settings, such as the Hou and Leblanc processes.
Today it is sustainable to obtain it from its natural minerals, the trona being the most abundant of these.
On the other hand, the more traditional method consisted of growing and burning sodium-rich plants and algae. Then, the ashes were bathed with water and subjected to heating until the product was obtained. From here came the famous soda ash.
Properties
Na 2 CO 3 is an odorless, hygroscopic white solid with a molecular weight of 106 g / mol and a density of 2.54 g / mL at 25 ºC.
Its properties change as it incorporates a water molecule into its crystalline structure. Since water can form hydrogen bonds and ions "make space" between them, the volume of the crystal increases and the density of the hydrate decreases. For example, for Na 2 CO 3 · 10H 2 O, its density is 1.46 g / mL.
Na 2 CO 3 melts at 851 ºC, decomposing according to the following equation:
Na 2 CO 3 (s) => Na 2 O (s) + CO 2 (g)
Again, although the CO 3 2– and Na + ions differ in size, their electrostatic interactions are very efficient and maintain a stable crystal lattice.
Water molecules "get in the way" of these interactions, and as a result, hydrates are more susceptible to breakdown than anhydride.
It is a basic salt; that is, when dissolved in water, it generates a solution with a pH greater than 7. This is due to the hydrolysis of CO 3 2–, whose reaction releases OH - in the medium:
CO 3 2– (aq) + H 2 O (l) <=> HCO 3 - (aq) + OH - (aq)
It is very soluble in water and in polar solvents, such as glycerol, glycerin, acetone, acetates, and liquid ammonia.
References
- Shiver & Atkins. (2008). Inorganic chemistry. In The elements of group 1. (Fourth edition., P. 265). Mc Graw Hill.
- scifun.org. (2018). Sodium Hydrogen Carbonate & Sodium Carbonate. Retrieved on April 8, 2018, from: scifun.org
- Wikipedia. (2018). Sodium carbonate. Retrieved on April 08, 2018, from: en.wikipedia.org
- PubChem. (2018). Sodium Carbonate. Retrieved on April 8, 2018, from: pubchem.ncbi.nlm.nih.gov
- Ciner Resources Corporation. (2018). Soda Ash. Retrieved on April 8, 2018, from: ciner.us.com
- Qniemiec. (May 7, 2010). Solvay process.. Recovered from: Wikimedia.org
- Peltier K. (July 3, 2018). Everything You Need to Know About Sodium Carbonite. Retrieved on April 8, 2018, from: thespruce.com
- Net Industries. (2018). Sodium Carbonate - Uses Of Sodium Carbonate. Retrieved on April 8, 2018, from: science.jrank.org