Lesson Video: Oxidization and Reduction Science

Video Transcript

In this video, we will learn how to identify and analyze oxidization and reduction reactions. We will learn how to define oxidization, reduction, oxidizing agent, and reducing agent in terms of gain and loss of oxygen, hydrogen, and electrons.

Oxidization and reduction are two chemical processes that can be thought of as opposite to each other. Both can be explained in a variety of ways. One of the simplest examples is the burning of carbon. When charcoal, a form of carbon, is burned, carbon is oxidized, forming carbon dioxide. Based on this, we can describe oxidization as the addition of oxygen. So the opposite reaction would be the loss or removal of oxygen. We can describe this process as reduction.

Oxygen can be removed from copper oxide to produce copper metal using hydrogen. As copper oxide has lost oxygen, we say that the copper oxide has been reduced. Therefore, we could describe this reaction as a reduction. However, the hydrogen has gained oxygen, forming water. So we say that hydrogen has been oxidized. So we can also describe this reaction as an oxidization.

In this reaction, copper oxide has been reduced and hydrogen gas has been oxidized. As the hydrogen gas is the agent that caused the reduction of the copper oxide, we can call it the reducing agent. Similarly, as the copper oxide is the agent that caused the oxidization of hydrogen, we call it the oxidizing agent. Therefore, the reducing agent gets oxidized and the oxidizing agent gets reduced.

We’ve looked at oxidization and reduction in terms of gain or loss of oxygen, but now let’s look at it in terms of gain or loss of hydrogen. Let’s take a look at the reaction between ammonia and bromine gas. Ammonia loses hydrogen, forming nitrogen gas. Bromine reacts with the hydrogen that ammonia loses, forming hydrogen bromide. As ammonia has lost hydrogen, we say that it’s oxidized or has undergone oxidization. We can define oxidization as a chemical process that increases the oxygen percentage or decreases the hydrogen percentage in a substance.

As bromine gains hydrogen, forming hydrogen bromide, we say that it’s been reduced or undergone reduction. We can define reduction as a chemical process that decreases the oxygen percentage or increases the hydrogen percentage in a substance. Although bromine is itself reduced, it also causes the oxidization of ammonia. So it is known as an oxidizing agent. An oxidizing agent provides oxygen or removes hydrogen from a substance during a chemical reaction.

Oxidization and reduction reactions occur in pairs, so if something is reduced, then something else will be oxidized. And if there is an oxidizing agent, there will also be a reducing agent. As ammonia causes the reduction of bromine, it is a reducing agent. A reducing agent provides hydrogen or removes oxygen from a substance during a chemical reaction.

Up until this point, we have considered oxidization in terms of the addition of oxygen or loss of hydrogen. However, some reactions involve oxidization and reduction but don’t contain oxygen or hydrogen. It’s also possible to define oxidization and reduction in terms of the gain or loss of electrons.

Let’s look at the combination of sodium and chlorine as an example. Sodium and chlorine are in their elemental form and are not charged. So, first of all, let’s calculate the electronic configurations for an atom of sodium and an atom of chlorine. If we look in the periodic table, we see that sodium has an atomic number of 11. This means that a neutral atom of sodium has 11 electrons. The first shell contains a maximum of two electrons. The second contains a maximum of eight electrons. And as there are 11 electrons in total, the remaining electron goes in the third shell. So sodium’s initial electronic configuration is 2,8,1.

If we find chlorine in the periodic table, we see that it has an atomic number of 17. So a neutral atom of chlorine has 17 electrons. Therefore, its electronic configuration is 2,8,7. When the two species react, sodium donates an electron to chlorine. The sodium atom becomes a sodium ion. It has a one-plus charge and an electron configuration of 2,8. As the chlorine atom gains an electron, it becomes a chloride ion. It has a one-minus charge and an electron configuration of 2,8,8.

As the sodium atom has lost an electron, we say that it is oxidized or has undergone oxidization. Oxidization is defined as a reaction that involves the loss of electrons from a substance. The chlorine atoms have gained electrons. So we say that chlorine is reduced or has undergone reduction. Reduction is defined as a reaction that involves the gain of electrons in a substance. As sodium is the agent that causes the reduction of chlorine, it is called the reducing agent. And as chlorine causes the oxidization of sodium, it is called the oxidizing agent.

It’s important to note that oxidization and reduction are concurrent processes. This means that they both occur at the same time. The oxidization of a substance cannot occur without the reduction of another.

Let’s look at another example of oxidization and reduction in terms of electrons. If magnesium reacts with copper sulfate, it can displace the copper, producing magnesium sulfate and copper metal. This is due to magnesium being higher than copper in the reactivity series. Copper sulfate and magnesium sulfate are both ionic species. A sulfate ion has a two-minus charge. So, to ensure an overall neutral charge, both copper and magnesium have a two-plus charge.

If we just look at magnesium, we see that it starts off neutrally charged and ends up with a two-plus charge. So magnesium has lost two electrons. We represent that magnesium has lost two electrons by placing those electrons on the right-hand side of the equation. This means that the charges on both sides of the equation are now balanced. This type of equation is called a half equation. And as it shows us that magnesium has lost electrons, we can clearly see that magnesium has been oxidized.

Half equations explicitly show how many electrons are lost or gained. So they make it considerably clearer as to which species are oxidized and which are reduced. Let’s now write a half equation for copper. Copper initially has a two-plus charge. It then forms neutral copper metal. To do this, it must gain two electrons. This half equation clearly shows us that copper two plus has been reduced.

We can actually combine these two half equations to give an overall ionic equation for this chemical reaction. We first need to consider the number of electrons. Fortunately, the number of electrons is the same in both half equations. So we can add the equations without making any adjustments. First, we need to add together the species on the left side of the equation, and then we need to add the terms on the right. As the number of electrons on each side of the equation is the same, they can be excluded.

As we can now consider oxidization and reduction in terms of electrons, we can also define oxidizing and reducing agents in terms of electrons. An oxidizing agent is a substance that can gain electrons from another substance during a chemical reaction. In the example we’ve just looked at, copper two plus has gained electrons so is itself reduced but is also described as an oxidizing agent.

A reducing agent is a substance that can lose electrons to another substance during a chemical reaction. So, for this example, magnesium loses electrons, so it is itself oxidized but is also described as a reducing agent.

We’ve now looked at quite a lot of different definitions. So before we move on to some questions, let’s do a quick summary. The definition of oxidization in terms of oxygen and hydrogen is a chemical process that increases the oxygen percentage or decreases the hydrogen percentage in a substance. A reduction, on the other hand, decreases the oxygen percentage or increases the hydrogen percentage. An oxidizing agent provides oxygen or removes hydrogen from a substance during a chemical reaction, whereas a reducing agent provides hydrogen or removes oxygen.

We can also define these words in terms of electrons, where oxidization is a reaction that involves the loss of electrons from a substance. Reduction, on the other hand, involves gain of electrons. An oxidizing agent can be defined as a substance that can gain electrons from another substance during a chemical reaction, whereas a reducing agent loses electrons to another substance.

There is another definition we can use for oxidizing agent and reducing agent, but it’s more general. An oxidizing agent can be defined as a substance that oxidizes another chemical species while being reduced itself, whereas a reducing agent reduces another chemical species while being oxidized itself.

Oxidization, reduction, oxidizing agent, and reducing agent were originally described in terms of oxygen and hydrogen. The definitions in terms of electrons came later. It’s important to note that even though not all reactions involving oxidation and reduction can be described in terms of oxygen and hydrogen, they can all be described in terms of electrons.

Now that we know how to identify and analyze oxidization and reduction reactions and how to define oxidization, reduction, oxidizing agent, and reducing agent, let’s look at a few examples.

Consider the reaction between sodium and chlorine: Cl2 gas plus two Na solid react to produce two NaCl solid. Which chemical species is oxidized in the reaction? (A) The sodium atoms, (B) the sodium ions, (C) the chlorine atoms, or (D) the chlorine ions.

If a chemical species has been oxidized, it means it has undergone oxidization, where oxidization is a reaction that involves the loss of electrons from a substance. Since we want to find out which species has been oxidized, we want to find out which species has lost electrons. Our starting materials are chlorine and sodium in their elemental form. Neither of these species are charged. The product is sodium chloride, commonly known as salt. It is an ionic species made of sodium ions and chloride ions. More specifically, the ions are Na+ and Cl−.

Chlorine started out as an uncharged species. But upon reaction with sodium, it became negatively charged. This means that chlorine gained electrons. Therefore, chlorine has not undergone oxidization; it has undergone reduction. Reduction can be defined as a reaction that involves the gain of electrons in a substance. Sodium, on the other hand, existed as a neutral starting material. But in the product, it is positively charged. Sodium atoms have to lose electrons to become positively charged sodium ions. So the sodium atoms undergo oxidization and are therefore oxidized.

So the answer to the question “Which chemical species is oxidized in the reaction?” is (A) the sodium atoms.

Which of the following descriptions can be used for an oxidizing agent? (1) Loses electrons, (2) gains electrons, (3) donates oxygen, (4) removes hydrogen, (5) donates hydrogen or removes oxygen. (A) 1, 2, and 5; (B) 1, 3, and 4; (C) 2 and 5; (D) 2, 3, and 4; or (E) 1 and 5.

An oxidizing agent can be generally defined as a substance that oxidizes another chemical species while being reduced itself. But we can define oxidizing agent, and therefore also reducing agent, oxidization, and reduction, in multiple ways, either in terms of gain or loss of oxygen, hydrogen, or electrons. In terms of oxygen and hydrogen, an oxidizing agent provides oxygen or removes hydrogen from a substance during a chemical reaction. As it provides oxygen, we see that (3), donates oxygen, is correct. And as it removes hydrogen, we see that (4), removes hydrogen, is also correct.

Description (5), which is “donates hydrogen or removes oxygen,” is the exact opposite to descriptions (3) and (4). So this is the description of a reducing agent, not an oxidizing agent. Therefore, we can rule out description (5) as it cannot be used for an oxidizing agent.

Now that we’ve addressed all options concerning oxygen and hydrogen, let’s look at the description of an oxidizing agent in terms of electrons. It is defined as a substance that can gain electrons from another substance during a chemical reaction. As it can gain electrons, we can see that description (2), gains electrons, can be used to describe an oxidizing agent. Option (1), however, loses electrons, is the opposite of this so is used to describe a reducing agent, not an oxidizing agent.

As we’ve determined that options (2), (3), and (4) are the correct descriptions used for an oxidizing agent, we can select option (D) 2, 3, and 4 as the correct answer to this question.

Now let’s look over the key points of this video. Oxidization can be considered the gain of oxygen, loss of hydrogen, or loss of electrons. Reduction can be considered the loss of oxygen, gain of hydrogen, or gain of electrons. Oxidizing agents are substances that can oxidize another substance while being reduced themselves, whilst reducing agents are substances that can reduce another substance while being oxidized themselves.

The electrons lost by the substance being oxidized are gained by the oxidizing agent. And the electrons gained by the substance being reduced are lost by the reducing agent. Lastly, oxidization and reduction are concurrent processes. This means that they happen at the same time.