Chemical Substances Reacting With Air
Sep 19, 2009 © Emily J. Foster
Many chemical reactions identified with the element Oxygen are described as oxidation-reduction
reactions, or simply redox reactions. This definition is fine but limited.
When chemistry first evolved from the ancient study of alchemy, many reactions were conducted with
chemicals exposed to air.
The reactive component of air was first produced by English philosopher and scientist, Joseph Priestley
(1673- 1804) and identified as the element oxygen by French chemist, Antoine Lavoisier
(1743- 1794). Reactions such as these were then described as oxidation reactions.
This article examines a group of chemical reactions called oxidation - reduction reactions, commonly
called redox reactions. These play a significant role in maintaining our environment.
Redox Reactions - Corrosion and Its Opposite
It is well known that steel structures tend to corrode, eventually producing the familiar orange-brown
flakes known as rust. The chemical reactions between water and the gases of the atmosphere that cause this
corrosion are known as redox reactions.
Conversely, the extraction of metals from their ores can be considered the opposite of the corrosion
of metals and are also redox reactions. Some common metals and their mineral ores are:
- Aluminium - Bauxite (Al2O3)
- Calcium - Limestone (CaCO3)
- Copper - Chalcopyrite (CuFeS2)
- Iron - Haematite (Fe2O3)
- Iron - Magnetite (Fe3O4)
- Zinc - Sphalerite (ZnS)
The Oxidation Reaction
In air, the reaction of carbon, sulfur, or iron always produced at least one oxide. For example, in the
case of iron reacting with oxygen forming the iron ore, haematite:
4Fe + 3O2 --> 2FeO3
This type of reaction was classified as oxidation due to the addition of oxygen; here the
element iron is considered oxidised to the iron ore.
The Reduction Reaction
Interestingly, because iron reacts with oxygen, there are no large deposits of elemental iron found on
earth. Instead, the iron our society uses everyday has been extracted from iron ores. To illustrate, the
production of iron from its mineral haematite can be represented by the reduction equation:
2FeO3 + 3CO --> 2Fe + 3CO2
That is, when oxygen is removed from a substance such as iron, the material is considered reduced.
Reduction cannot occur without oxidation at the same time. In the above reaction, it is the carbon
monoxide that has gained oxygen and is oxidised.
In the above two reactions, it is important to note that oxidation and reduction always occur in pairs
and simultaneously.
Improved Definition of Redox Required
While the definition of oxidation as the addition of oxygen was adequate for combustion reactions
occurring in air, many similar reactions not involving oxygen as a reactant have since been
investigated.
For example reactions involving sulfur, chlorine, sodium and others. Should these be called
"sulfonation", "chlorination", and so on? It seems naming all these reactions as
"oxidation" after oxygen does not focus on what these reactions have in common, nor does it
provide a theoretical explanation of the processes involved. A better definition was required that focuses
on electron transfer
in redox reactions.
References:
- "Heinemann Chemistry 1 - VCE Units 1 & 2". Nicole Lukins et al., Heinemann Harcourt
Education, 4th Edition. 2006.
- "Chemistry for Dummies" John T. Moore. Wiley Publishing, Inc. Hoboken, NJ. 2003.
The reader might be interested in another article
chemicals in the home , where everyone probably comes into contact with more chemicals and chemistry
in their own home than at any other place.
The copyright of the article Oxidation Reduction Reactions: Chemical Substances Reacting With Air
is owned by Emily J. Foster. Permission to republish in print or
online must be granted by the author in writing.
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