CHEMISTRY BEHIND THE ACID RAIN

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Author: Alfredsito94.
Edited by @madridbg, by changing size and text.

Welcome readers of Hive.blog, in this issue we will be talking about the Acid Rain, one of the induced natural phenomena that has come to cause great economic damage to society, as well as biological damage to the environment, where chemistry and its inventiveness plays a preponderant role on this alarming fact.

INTRODUCTION

The inventiveness of humanity in support of the scientific principles of chemistry as a science has brought great advances in technology, pharmaceuticals and agriculture to society. However, every day we read and hear in the media that chemistry is primarily responsible for the environmental problems the planet presents.

In this sense, acid rain as an induced phenomenon is linked to excessive consumption and dependence on products extracted from fossil substances, in addition to derisory practices related to the burning and degradation of the planet's biotic systems.

Therefore, to fully understand the phenomenon being studied, it is necessary to instruct the reader on the characteristics that a substance must possess to be considered as acidic, which is framed in the Acid-Base theory of Bronsted-Lowry

So in the course of this topic we will make a tour of the main chemical substances that make up acid rain, as well as the problems it has caused to society and the environment.

BEHAVIOR OF WATER, IN THE FACE OF THE ACID-BASE THEORY OF BRONSTED-LOWRY

J.N. Bronsted, a Danish chemist and physicist, and T.M. Lowry, born in Great Britain, established that any substance (ion or molecule) that has the capacity to transfer a proton is considered to be an acid, while that substance that has the capacity to accept a proton is defined as a base. [1]

Correspondingly, water as a universal solvent, has the capacity to behave like an acid and at the same time as a base. It behaves as a base when in the presence of an acidic substance and vice versa, and is therefore considered an amphoteric substance, allowing it to self-dissolve into conjugated pairs, i.e. H2O (acid) and OH- (base) / H3O+ (acid) and H2O (base).


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Equation 1: Self-dissociation of water
Author: Chang, (2010).

If we analyze the equation, we can establish that while a water molecule behaves like an acid, other molecules behave like a base, forming the hydronium (H3O+) and hydroxide (OH-) ions, a reaction that is reversible and continuous when the hydronium ions give up an electron to the hydroxide ions to restart the process.


pH AS AN ACIDITY MEASUREMENT

The term pH comes from the French puissance d'hydrogène which means power of hydrogen, therefore, the measure of acidity of a substance is determined by the concentration of hydronium ions (H3O+) in aqueous solution, operationally the pH can be determined or calculated by applying the method of Sorence, which states that the pH is the negative logarithm of the concentration of hydronium ions in (mol/L). [3]

On an experimental level, the pH of a solution is measured with an apparatus called a peachimeter which is governed by a scale ranging from 1 to 14, with 7 being the neutral value, the numbers before this are established for acidic substances and the numbers after 7 are used for basic or alkaline substances. See figure 2.


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Figure 2. Peachimetro and the pH scale.
Author: @madridbg, published through Poder Point 2010.
Using public domain images.


ACID RAIN AS A CHEMICAL PHENOMENON


Nowadays, acid rain has become a controversial issue and although we all know the causes of its formation, in this section we will describe the main chemical components present in this phenomenon, as well as the reactions involved.

Under normal conditions, water from lakes and seas evaporates and condenses into clouds which then fall under their own weight, with a pH close to 5.6, due to dissolved carbon dioxide (CO2). However, at present this value is in a range of 3 to 3.5 in industrialized areas, considerably increasing the level of acidity. Experts believe that this variation is largely due to the industrialization of cities, the mass use of cars, power plants and foundries that release large amounts of chemical waste into the air.

The decrease in the pH value of rain has caused great damage to the aesthetic system of large cities, with the degradation of the statues and facades of homes and buildings due to the dissolution of carbonates present in these buildings. Similarly, it attacks the soil and lowers its pH, generating difficulties in obtaining quality fruit, in addition to the investment that farmers must make to restore the alkaline pH of the substrates.

In addition to the above, a large number of fish have disappeared as a result of acid rain, since a large part of the aluminum in the rocks dissolves and is carried to the rivers and lakes where it falls into the gills of the fish in the form of aluminum hydroxide (Al(OH)3), causing their death.


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Figure 3. Damage caused by acid rain.
Author: @madridbg, published through Power Point 2010.
Using public domain images.

These problems are largely due to the set of chemical reactions that occur during the process and will be described according to the following sequence of equations:


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Equation 2. Sulfuroso Acid Formation


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Equation 3. Sulfurico Acid Formation

Equations 2 and 3 are the consequence of the large amounts of sulfur dioxide and trioxide that are released into the air as a result of the burning of fossil substances with high sulfur content from smelters and power plants. These substances, in contact with rainwater, dissolve and give rise to the formation of sulfuric and sulfuric acid On the other hand, the release of nitrogen oxides, coming from the plants where coal is burned and from the exhausts of the automobiles generates nitric acid (HNO3) that together with the already formed sulfuric acid aggravates the problem. See equation 4.


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Equation 4. Nitric Acid Formation

It is necessary to emphasize that sulfur and nitrogen oxides have always been present in the atmosphere since volcanoes and lightning produce them naturally and keep them in balance, the problem starts when the quantities increased drastically by human actions.

CONTRIBUTIONS OF THE SUBJECT

In accordance with the approaches made, it can be determined that the subject matter allows a broader view of a problem that affects us all, such as acid rain, and also allows the understanding of the set of chemical reactions that are immersed in the phenomena studied, associating the concepts of chemistry in each section of the publication.

BIBLIOGRAPHY CONSULTED

[1] Chang, R. (2010). Chemistry. Tenth edition. McGraw-hill Interamericana editors. ISBN: 978-607-15-0307-7.

[2] Garcés, L and Hernández M. (2004). Acid rain: a physicochemical phenomenon of local occurrence. Lasallian Research Journal, vol. 1. No. 2. Lasallian University Corporation. Antioquia, Colombia.

[3] Granados D; López, G and Hernández M. (2010). Acid rain and forest ecosystems. Chapingo Magazine. Series Ciencias Forestales y del Ambiente 16(2): 187-206.

[4] McMURRY E., John and Fay C., Robert. (2008). General chemistry. Fifth edition PEARSON EDUCACIÓN, México, 2009 ISBN: 978-970-26 1286-5.

[5] Lopez, A (2013). Absorption of carbon dioxide, at high partial pressures, by aqueous solutions of alkanolamine binary mixtures. University of Jaén. Faculty of Experimental Sciences.

[6] Ralph, H. Petrucci, William S. Harwood, E. Geoffrey Herring. (2003). GENERAL CHEMISTRY. Eighth edition. PEARSON EDUCATION. S.A., Madrid.


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Gracias @oscurity por la observación, seria oportuno me sugieras algunas comunidades. Saludos

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