THE CHEMISTRY BEHIND WATER TREATMENT: A THEORETICAL AND PRACTICAL APPROACH

Greetings and welcome back to this space of scientific dissemination, the topic that concerns us this time is associated with those chemical processes that are behind the purification of water and that are very useful to prevent the proliferation of diseases through aqueous media.

In this sense, it is necessary to understand that in the nature of our daily life, we are surrounded by processes where chemical systems that meet properties similar to solutions are constituted daily, so it is common to observe the formation of ions in these systems and even more so in nature where the conditions are not completely controlled.

In such a way that this type of system at the level of our nature is very common to get them, for two very obvious reasons, in the first instance water is cheap and is a liquid capable of dissolving a large number of chemicals, on the other hand, in the middle of aqueous solutions substances are in the form of ions, hence they can act in different reactions and chemical processes, in this sense, it is normal to observe aqueous processes from the depths of the sea to the interior of any living being.

So if we try to make a mental image of the process of the solutions at the molecular level, we realize that its structure is formed by particles of a substance in greater proportion to which chemically is called solvent and other particles whose quantities are lower and that we will call solute, This is distributed randomly and one envelops the other, entering into a solvation system that make possible the chemical solution, at this point, at theoretical and experimental level is expected the formation of clusters of atoms that acquire net electric charges by loss of electrons.

An example of the above is represented by oxygen dissolved in seawater, where water molecules are close to each other, while oxygen molecules are dispersed among them.

Likewise, aqueous solutions are capable of forming precipitation reactions when some dissolved salts are present, as in the example of sodium chloride in seawater; however, when the salt present is not very soluble, it tends to fall to the bottom of the place where the solution is found; this behavior of the substance is known as precipitate, the clearest proof of this behavior is represented by silver chloride, which, being not very soluble, ends up precipitating due to gravitational issues.

Based on the above, aqueous media allow the development of various chemical processes ranging from oxidation-reduction to acid-base reactions and it will be the latter where we will focus our approach to explain the treatment of water, so that the idea of acids and bases, also called alkalis, are processes that began to run in antiquity, when from certain plants began to extract alkaline substances from the ashes of the same.

Hence, in practical terms, an acid can be identified by its capacity to react with metals and carbonates, by the turning it causes on litmus paper and by its flavor. However, in chemical terms, acids are substances capable of yielding hydronium ions in the middle of an aqueous solution, as we can see in the following chemical equation, which allows us to model the behavior of hydrochloric acid when dissolved in water, generating hydronium and chloride ions.

On the practical level, bases are identified by their bitter taste, they are slippery and change the color of litmus paper, on the other hand they are considered as substances capable of producing hydroxyl ions in aqueous solution, so that these substances upon contact with water dissociate completely as we can see with the case of sodium hydroxide, which produces sodium ions and hydroxyl groups when they enter into solution.

In this sense, when comparing the properties of acids and bases, we realize that one of the most striking features is their ability to neutralize the properties of one over the other, so that when they react with each other they end up generating a respective salt, a behavior that extends throughout the different chemical processes in which these substances are immersed.

Therefore and starting from the constructs described above, we have to know that water in many cases is not simply water, as it often has many impurities that make it unsuitable for certain purposes and to exemplify the above, We can establish that a chemist during his experimental processes does not use tap water to prepare the respective dissolutions of silver nitrate, since in doing so the dissolution would be covered with a milky shadow product of the reaction between the silver ions and the dissolved chlorides, thus generating the formation of silver chloride as impurities throughout the process.

On the other hand, the same tap water can be ingested without problem, so that it has been provided with another utility, now with respect to the procedure of purification of the vital liquid, this depends on the use that will be given to it or how it has been used previously, hence the water that has been used in industrial processes may require a previous treatment, the water intended for domestic use.

Likewise, water used in a chemical plant must be subjected to a more complex treatment than water that has been used at the residual level in domestic systems; however, all treatments have something in common, since during each process the aqueous chemical reactions previously studied throughout this paper will be present.

So to understand the above, let's approach the following case study: We will assume the removal of iron from drinking water coming from deep wells, according to international regulations, the recommended limit of iron present in drinking water is 0.3mg/L, however, some water wells contain a concentration of 35 mg of iron per liter of water.

Based on the above, the work methodology to eliminate excess iron consists of transforming chlorinated water into a slightly basic solution using slaked lime, chemically known as calcium hydroxide, followed by a process of oxidation of ferrous and ferric ions by the action of hypochlorite ion, and finally, the iron is precipitated in the form of ferric hydroxide from the basic solution previously prepared.

Consequently, we must bear in mind that this is only one of the methods applied and it depends on the type of pollutant or impurities present, hence it is to be expected that the processes vary, since we can apply chemical methodologies for the elimination of oxygen from thermal power plant water, elimination of phosphates from wastewater, destruction of cyanide ions in industrial operations, among others.

So chemistry offers us a wealth of possibilities in this area, hence the need to continue advancing in order to improve and control every aspect of our daily life.

[1] Rincón Flórez, J. F.; Fonseca Becerra, J. E. & Carvajal Medina, R. J Calculation of thermodynamic parameters for military explosives. Application of thermodynamic fundamentals and properties of military explosives.Artículo: Acceso Online

[2] Chang, R. (2010). Química. Decima edicion. McGraw-hill Interamericana editores. ISBN: 978-607-15-0307-7.

[3] Ralph, H. Petrucci, William S. Harwood, E. Geoffrey Herring. (2003). QUIMICA GENERAL. Octava edición. PEARSON EDUCACIÓN. S.A., Madrid.

[4] WADE,LEROY. (2011). . ORGANIC CHEMISTRY. VOLUME 2. SEVENTH EDITION. PEARSON EDUCATION, MEXICO, 2011 ISBN: 978-607-32.()793-5.