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Redox (Oxidation-Reduction) Reactions: Definitions and Examples

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  • 0:05 Reduction and Oxidation
  • 1:54 Redox Reaction Examples
  • 6:06 Lesson Summary
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Lesson Transcript
Instructor: Jill Ross

Jill has a B.S. in Health Studies and an M.Ed. in Instructional Design and Technology. She's a biology teacher and library media specialist.

This short video will explain oxidation-reduction reactions, or redox reactions for short. The focus is on how electrons are transferred during redox reactions. Learn some neat mnemonic devices to help you remember when an atom is oxidizing or reducing.

Reduction and Oxidation

Are you familiar with the reaction that forms table salt? Do you know what kind of reaction it is? This lesson is Redox Reactions and is part of the review of inorganic chemistry.

There is a specific type of chemical reaction called oxidation-reduction reactions (or redox reactions for short). In these reactions, electrons are transferred from one reactant to another. So, simply put, electrons are lost from one substance and gained by another.

Oxidation refers to the loss of electrons from a substance, while reduction refers to the gain of electrons by a substance. These two processes cannot occur without the other. That being said, if there's a reduction reaction, there must be an oxidation reaction. Or, if there's an oxidation reaction, there must be a reduction reaction. Don't be confused by reduction being a gain, though. Adding electrons is called reduction because the overall charge is reduced - more electrons means the substance becomes more negative.

For example, carbon typically has six protons, six neutrons and six electrons. If we reduce carbon, it gains an electron. If you remember, electrons are negative, so adding another electron would make seven, and the carbon atom would become more negative. We would say that the carbon's overall charge has decreased, or it has been reduced.

An easy way to keep it straight is by using the mnemonic device 'LEO the lion says GER.' LEO stands for 'lose electrons oxidation.' GER stands for 'gain electrons reduction.' So, oxidation is when an atom loses electrons, while reduction is when an atom gains electrons.

Redox Reaction Examples

The easiest way to fully understand redox reactions is to look at some examples. So let's start by looking at the reaction that forms table salt. Sodium is oxidized and loses an electron to have a +1 charge; meanwhile chlorine is reduced because it gains the electron to have a -1 charge. The redox reaction creates two ions with opposite charges that are attracted to one another and create sodium chloride, or table salt.

At this point it's also important to discuss reducing and oxidizing agents. A reducing agent donates electrons or reduces another substance. So, in the case of our table salt reaction, sodium is the reducing agent. An oxidizing agent accepts electrons or oxidizes another substance. So, in the case of our table salt reaction, chlorine is the oxidizing agent. An oxidizing agent gains electrons, and an oxidizing agent is reduced.

A silly mnemonic device to help you remember this is 'Ryan already likes eating ostriches. Ostriches are getting eaten regularly.' The mnemonic stands for a reducing agent loses electrons and is oxidized, while an oxidizing agent gains electrons and is reduced.

The formation of hydrogen fluoride is an example of a redox reaction.
Redox Reactions Examples

Another example of a redox reaction is the formation of hydrogen fluoride. We can break the reaction down to analyze the oxidation and reduction of reactants. The hydrogen is oxidized and loses two electrons, so each hydrogen becomes positive. The two electrons are gained by fluorine, which is reduced. This makes the two fluorines negative. The oxidation of hydrogen and reduction of fluorine creates two ions with opposite charges of +1 and -1. Opposites attract, so they combine and form hydrogen fluoride.

But not all redox reactions are cut and dry with gaining and losing electrons; electron sharing exists with covalent bonding. With covalently bonded molecules, whether a substance oxidizes or reduces is based on the atom's pull on electrons, or electronegativity. Electronegativity is the attractive force that an atom exerts on electrons. It's based on the atomic number and the distance of valence electrons in an atom.

We've already talked about electronegativity when discussing bonding. When atoms have similar electronegativity, they use nonpolar covalent bonding. But, in ionic bonding, the two atoms have very different electronegativity numbers, leading to them exchanging an electron. Then, when electronegativity numbers are somewhere in the middle, the atoms will form polar covalent bonds.

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