Redox Reactions - Online Tutor, Practice Problems & Exam Prep

Redox reactions, short for oxidation-reduction reactions, involve the transfer of electrons between molecules. Oxidation is the loss of electrons, while reduction is the gain of electrons. These processes occur simultaneously, as one molecule loses electrons while another gains them. Electron carriers like NADH and FADH₂ transport electrons during cellular respiration, acting as "electron taxi cabs." NAD⁺ and FAD are the oxidized forms of these carriers, having lost electrons. Understanding these concepts is crucial for grasping metabolic processes and energy transfer in biological systems.

Redox Reactions

In this video, we're going to introduce redox reactions. Redox is really just short for oxidation reduction. You can see that the red in redox is for the red in reduction, and the ox in redox is for the ox in oxidation. Oxidation reduction and redox reactions refer to the same exact thing, and they involve the transfer of electrons between molecules. The symbol for electrons is an e^-.

Recall from our previous lesson videos that electrons are negatively charged. Within oxidation reduction, you can see the two words, oxidation and reduction, of course. Oxidation is the process of losing one or more negatively charged electrons, whereas the process of reduction is the process of gaining one or more negatively charged electrons. If something is gaining negatively charged electrons, then that means that its overall charge is going to be reduced because it's gaining negatives.

Oxidation and reduction reactions always occur simultaneously, which means that they always occur at the same exact time. If something is losing electrons, then something else must be gaining those electrons. This is why oxidation reduction reactions always go hand in hand with each other. Let's take a look at our example down below at these redox reactions or oxidation reduction reactions.

All you really need to remember is "Leo the lion goes," and that's because if you can remember that "Leo the lion goes ger," then you'll be able to remember that anything that loses electrons is going to be oxidized, and oxidation refers to anything that loses electrons, whereas ger refers to gaining electrons is reduction. Anything that gains electrons is going to be reduced, meaning its charge is going to be reduced because it's gaining negatively charged electrons. Just by remembering "Leo the lion goes," you'll be able to remember that oxidation is losing electrons and reduction is gaining electrons. You can see that Leo the lion is going down below in the image.

By remembering this, you should be set on your problems for redox reactions. Over on the right-hand side, what we have is an image to show you that oxidation and reduction reactions always go hand in hand. You can see here that we have a person that has some electrons in their hands right here, and this little blue circle with the negative charge in it is representing our electron. If this person is giving up the electron and giving it to this person over here, then this person will be gaining electrons, meaning that it will be reduced, whereas the person who is giving up electrons, giving them away, they are losing electrons and because they are losing electrons, they are being oxidized. The oxidation reduction reactions will always go hand in hand, almost like a person giving a gift away.

If someone's giving away a gift or losing a gift, that means that someone else is gaining the gift. Oxidation and reduction reactions will always go hand in hand, just like what you can see here in this image. This here concludes our introduction to redox reactions, and we'll be able to learn more about them as we move forward in our course. I'll see you all in our next video.

Redox Reactions Example 1

So here we have an example problem that's asking which of the following molecules is oxidized and which is reduced? Notice that we have molecule A over here and molecule B, and they are undergoing a chemical reaction. Notice that we have these four potential answer options over here. Of course, we need to recall from our last lesson video that when it comes to oxidation-reduction reactions or redox reactions, all we need to remember is "Leo the lion goes ger." If we remember "Leo the lion goes ger," then we'll be able to remember that oxidation is when a substance loses electrons and reduction is when a substance gains electrons.

Looking at this reaction here between molecule A and molecule B, notice that molecule A is starting with an electron here in blue, and molecule B seems to not have that electron. After this reaction, molecule A is actually donating its electron to molecule B. Therefore, molecule A is losing an electron by the end of the reaction, whereas molecule B is gaining the electron. Because molecule B is gaining the electron, that makes it reduced, and because molecule A is losing the electron by the end of the reaction, that makes molecule A oxidized. We need to choose the option that corresponds with that, and notice option A says molecule A is oxidized whereas molecule B is reduced, and that is going to be the correct answer to this example problem. We can go ahead and mark A here as correct, and that concludes this example problem. I'll see you all in our next video.

Oxidation is the _________________________, and reduction is the _________________________.

• A. Gain of electrons; Loss of electrons.
• B. Gain of protons; Loss of protons.
• C. Loss of electrons; Gain of electrons.
• D. Gain of oxygen; Loss of oxygen.

When glucose donates electrons to NAD⁺ creating NADH, the glucose molecule becomes:

• A. Hydrolyzed.
• B. Oxidized.
• C. Neutral.
• D. Reduced.

Electron Carriers: NADH & FADH2

In this video, we're going to introduce electron carriers, specifically NADH and FADH₂. It's important to note that many biological processes that we're going to talk about moving forward in our course, including cellular respiration, conduct redox reactions using electron carriers. These electron carriers are helpful to perform redox reactions. Electron carriers such as NADH and FADH₂ are each going to carry or transport a maximum of 2 electrons. These NADH and FADH₂ electron carriers can shuttle electrons to different locations within a cell, kind of like an electron taxi cab.

You can think of NADH and FADH₂ as electron taxi cabs, and we'll be able to see that down below in our image. It's also important to note that NAD⁺ and FAD are the oxidized forms of NADH and FADH₂ respectively. Recall that in oxidation, symbolized by "Leo," the lion goes "ger," and "Leo" represents oxidation. This means that NAD⁺ and FAD are both going to have fewer electrons. They're going to have lost electrons in comparison to NADH and FADH₂.

Let's take a look at our image down below to clear some of this up. These electron carriers that we're going to be talking about, NADH and FADH₂, really act like electron taxicabs. Notice here in this image, we're showing you an electron taxicab. On the left-hand side, notice that we have the empty form of the electron taxicab. But of course, when this electron taxicab picks up its 2 passengers, these 2 electrons, it's going to become a full taxicab.

Over here we have the 2 electrons inside of this electron taxicab. NADH will form when the oxidized form, the NAD⁺, the empty taxi cab version, picks up its 2 passengers, these 2 electrons along with a hydrogen ion, and it forms NADH. You can see that NADH is carrying these 2 electrons, but it also picks up a hydrogen atom as well. When we look at FAD, this is the empty taxicab version of FAD, this electron carrier, but when it picks up its 2 passengers, these 2 electrons, it also picks up 2 hydrogen ions as well and it becomes FADH₂, the full taxicab version of this electron carrier.

One way to help you guys remember, a helpful memory tool to remember that NADH and FADH₂ are the full taxicab versions, is to just think that NADH and FADH₂ are just a little bit heavier because they're gaining electrons and hydrogens. The ones that have "h" in them are going to be a little bit heavier, and these are the full taxicab versions. What you'll learn as we move forward in our course talking about cellular respiration is that during cellular respiration, these electrons carried by NADH and FADH₂ are going to go to what's known as the electron transport chain, which is the final stage of cellular respiration. We'll talk more about this as we move forward in our course.

But for now, you can see that this full electron taxicab here, notice one of the electrons is asking, "Where are we going?" and the other electron is responding, "To the electron transport chain, duh." Remember moving forward in our course we're going to learn that these NADH's and FADH₂'s are going to take their electrons to the electron transport chain during cellular respiration. This concludes our brief introduction to electron carriers NADH and FADH₂, and we'll be able to get some practice applying the concepts that we've learned here as we move forward in our course. So I'll see you all in our next video.

An electron carrier before it harvests energy from glucose molecules in a series of gradual steps is:

• A. Pyruvate.
• B. AMP.
• C. ATP.
• D. NAD⁺.
• E. NADH.

Here’s what students ask on this topic:

What are redox reactions and why are they important in biological systems?

Redox reactions, short for oxidation-reduction reactions, involve the transfer of electrons between molecules. Oxidation is the loss of electrons, while reduction is the gain of electrons. These processes occur simultaneously, as one molecule loses electrons while another gains them. Redox reactions are crucial in biological systems because they play a key role in metabolic processes and energy transfer. For example, during cellular respiration, electron carriers like NADH and FADH₂ transport electrons to the electron transport chain, facilitating the production of ATP, the energy currency of the cell.

How do NADH and FADH₂ function as electron carriers in cellular respiration?

NADH and FADH₂ function as electron carriers by transporting electrons during cellular respiration. They act like 'electron taxi cabs,' picking up electrons and hydrogen ions. NAD⁺ and FAD are the oxidized forms, which gain electrons and hydrogen ions to become NADH and FADH₂, respectively. These carriers then shuttle the electrons to the electron transport chain, the final stage of cellular respiration, where the electrons are used to produce ATP. This process is essential for energy production in cells.

What is the mnemonic 'LEO the lion says GER' and how does it help in understanding redox reactions?

The mnemonic 'LEO the lion says GER' helps in understanding redox reactions by simplifying the concepts of oxidation and reduction. 'LEO' stands for 'Loss of Electrons is Oxidation,' and 'GER' stands for 'Gain of Electrons is Reduction.' This mnemonic aids in remembering that oxidation involves losing electrons, while reduction involves gaining electrons. Since these processes occur simultaneously, the mnemonic helps students quickly recall the fundamental principles of redox reactions.

What is the difference between NAD⁺ and NADH in terms of their roles in redox reactions?

NAD⁺ and NADH play different roles in redox reactions. NAD⁺ is the oxidized form, meaning it has lost electrons. It acts as an electron acceptor, picking up electrons and a hydrogen ion to become NADH. NADH, the reduced form, carries these electrons to other parts of the cell, such as the electron transport chain during cellular respiration. This transfer of electrons is crucial for producing ATP, the cell's energy currency. Thus, NAD⁺ and NADH are essential for energy transfer and metabolic processes.

Why do oxidation and reduction reactions always occur simultaneously?

Oxidation and reduction reactions always occur simultaneously because the transfer of electrons must be balanced. When one molecule loses electrons (oxidation), another molecule must gain those electrons (reduction). This simultaneous occurrence ensures that the total number of electrons remains constant. For example, in cellular respiration, when glucose is oxidized, electron carriers like NAD⁺ and FAD are reduced to NADH and FADH₂, respectively. This interdependence is fundamental to maintaining the balance of electron transfer in biological systems.