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What is sodium carbonate?

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 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 [Ne] 3s 1 valence configuration . The electron of the 3s 1 orbital is easily detached by other elements in 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 that 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.

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 2–  ion there are two Na + ions .

Structure of sodium carbonate

Sodium carbonate

In the upper image the structure of Na 2 CO 3 anhydride (also called calcined soda) is represented. The purple spheres correspond to Na + ions , while the black and red spheres correspond to CO 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 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.

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.

Uses / Applications of Sodium Carbonate

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 hard, non-rough 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 break down 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 skin cleansing.

Synthesis of sodium carbonate

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 be 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 of sodium carbonate

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. As water can form hydrogen bonds and the ions “open 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 CO 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, dissolved in water, it generates a solution with a pH greater than 7. This is due to the hydrolysis of CO 2– , the reaction of which releases OH  in the medium:

CO 2– (aq) + H 2 O (l) <=> HCO  (aq) + OH  (aq)

It is very soluble in water and in polar solvents, such as glycerol, glycerin, acetone, acetates, and liquid ammonia.

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