Can you believe we are on the last chapter of the textbook already? Our chemistry lessons are flying by.
Textbook Reading: Chapter 16, Oxidation and Reduction on pp. 577- 603, paying particular attention to the Rules for Assigning Oxidation States on page 581.
Oxidation and reduction are fundamental to chemistry, but can be a bit complicated to understand. This is probably why the author introduces them in the final chapter after you have a good understanding of other concepts.
During many chemical reactions, electrons are moved around. When an atom loses electrons, chemists say it has been oxidized. When an atom gains electrons during a reaction, it is said to be reduced.
The first question you might have is why is gaining electrons called reduction. Actually, you have to go back 500 years or so to the foundations of chemistry through alchemy to find out the answer.
(Image in the public domain from Wikimedia)
When early metal workers melted iron ore, the iron oxides in the ore released oxygen gas and the process resulted in pure iron. Because mass was lost (there was less iron produced that ore used), it was called a reduction.
The chemical equation:
2 Fe2O3 -> 4 Fe (solid) + 3 O2 (gas)
If we consider what is happening to the iron atoms, we realize the Fe ions are gaining electrons to become pure iron metal.
4 Fe+2 + electrons –> 4 Fe0
A few hundred years later, early chemists realized that oxygen was the gas being released and that adding oxygen to metals caused the formation of metal oxides. This led to the idea that the reverse of reduction involved gaining of oxygen, or oxidation.
We now know that oxygen doesn’t have to be involved in oxidation-reduction reactions and that reduction is actually the gain of electrons by atoms, but we are stuck with those historical, relatively-inaccurate names.
All is not lost, however, because chemistry students have come up with some tricks to remembering the terms.
1. This is a common way to remember the terms:
(Lion image by Petr Kratochvil at publicdomainpictures.net)
LEO = Loss of Electrons is Oxidation
GER = Gain of Electrons is Reduction
2. Another version is OILRIG , which is short for Oxidation is Loss (of electrons) and Reduction is Gain (of electrons).
3. You may also think of a gain of electrons as increasing a negative charge, or in other words, reducing the charge of the ion to a smaller number.
Why look at Reduction-Oxidation or Redox?
How easily a metal loses electrons will help predict how reactive it is and its behavior when mixed with other elements. Redox states help chemists figure out the likelihood certain reactions will occur.
Another use is to figure out the amount of certain substances in samples by redox titration, similar to acid-base titration. For example, it is possible use a redox titration to find out the amount of vitamin C (ascorbic acid) in different types of food or juice.
Let’s finish up with a discussion of Redox Reactions by Mr. Anderson of Bozeman Science.
Please let me know if you have any questions or comments about oxidation-reduction.