Rusting – Chemical Reactions in Your World

In our daily life, we encounter many chemical reactions, which may be classified as acid-base reactions, oxidation-reduction reactions or precipitation reactions (Brown, 2015).  There are many chemical reactions that occur in our daily life and which can be classified into the three categories studied in class. Examples of chemical reactions that occur in our daily life include photosynthesis, which is an energy generation process that involves the combination of carbon dioxide and water. Other examples include rusting and combustion of domestic gas. In this post, a discussion of chemical reactions involved in rusting process will be discussed.

            Rusting is a common reduction-oxidation (redox) chemical reaction that occurs when air combines with iron in the presence of water. When iron is exposed to air in presence of moisture, it combines with the compounds in a chemical reaction process that leads to formation of a reddish brown oxide commonly known as rust. The phenomenon is observed in the pipes of our water systems, farm implements and even parts of vehicles. It is an expensive chemical reaction as it causes increased wear and tear, leading to lose of money in replacement and purchase of new items.

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            The chemical process involved in rusting is classified as redox reaction. According to (Beran, 2011) redox reactions are often accompanied by changes in color more than is observed in acid-base reactions. Whereas there is a transfer of protons (H+) in acid-base reactions, the authors asserts that in redox reactions, there is a transfer of electrons (e) between the substances involved in the chemical reaction process (pp. 309). The transfer of electrons results in the change in the oxidation numbers of the elements involved in the chemical reactions. It is due to these transfer or exchange of electrons that makes the process to be termed as redox, since the elements in redox reaction that has its oxidation number being decreased is said to be reduced, while the one whose oxidation number increases is said to be oxidized hence the term redox reaction.

            In redox reactions, the oxidized element(s) have to lose its electrons to the element(s) that are reduced. The element(s) that gains electrons is called oxidizing agent, while the one that loses electrons is termed as the reducing agent. Beran (2011) asserts that in the redox reaction, electrons are never considered as reacting elements but are merely transferred or gained. The rusting process is a good example of a redox reaction that involves the transfer of electrons between the elements in the chemical reaction.

            Rusting occurs as a result of oxidation of iron, which occurs in a two step process. According to (Clugston & Flemming, 2011) the first process in rusting is the oxidation of iron leading to formation of iron (II) ions and reduction of oxygen to form hydroxyl ions. This process can be represented in the chemical equations below:

Fe (s) → Fe2+ (aq) + 2 e …………………………………………………….. (i)

O2 (g) + 2H2O (l) + 4 e→ 4OH (aq)……………………………………… (ii)

Combining the two equations and balancing them by first multiplying the first equation by two, the electrons in the left and right hand of the new equation cancels, resulting in the third chemical equations shown below.

2 Fe (s) + O2 (g) + 2H2O (l) →   2Fe2+ (aq) + 4 OH (aq) …………………… (iii)

The resulting iron (II) hydroxide undergoes rapid oxidation process to form complex red-brown hydrated form of iron (III) oxide, which is commonly termed as rust. The hydrated red-brown iron (III) oxide is represented by the complex formula Fe2O3.xH2O. As more rust peels off the surface of iron, it exposes more of the underneath to more rusting, which eventually leads to perforation normally seen in water pipes. From the chemical reaction, the nature of redox reaction can be seen in the third equation as iron loses four electrons, whereas the same number is gained in hydroxyl ions.

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