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. Key electron carriers, NADH and FADH₂, transport electrons during cellular respiration, acting like "electron taxi cabs." NAD⁺ and FAD are their oxidized forms, having lost electrons. Understanding these concepts is crucial for grasping metabolic pathways 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. Thus, oxidation-reduction and redox reactions are referring to the same exact thing. They refer to reactions that involve the transfer of electrons between molecules. This symbol here is the symbol for electrons, which is an "e" with a negative sign, because 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. We're going to define what each of these words is referring to. Oxidation is the process of losing one or more negatively charged electrons. Whereas the process of reduction is gaining one or more negatively charged electrons. If something is gaining negatively charged electrons, then its overall charge is going to be reduced because it's gaining negatives. That is why reduction is the process of gaining negatively charged electrons.

It's also really important to note that oxidation and reduction reactions always occur simultaneously, which means they always occur at the same exact time because 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. So let's take a look at our example below at these redox reactions or oxidation-reduction reactions. When it comes to redox reactions, all you need to remember is "Leo the lion goes ger", 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 just refers to anything that loses electrons. Whereas the "ger" here 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.

By remembering "Leo, the lion goes ger", you'll be able to remember that oxidation is losing electrons and reduction is gaining electrons. Below we have a little image of Leo here, and you can see that Leo the lion is going "ger". By remembering this, you should be set on your problems for redox reactions. Over here on the right-hand side, we have an image to show you that oxidation and reduction reactions always go hand in hand. You can see 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. You can see that 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 they will be reduced, whereas the person that is giving up electrons, they are losing electrons and because they are losing electrons, they are being oxidized. The oxidation-reduction reactions will always go hand in hand because it's 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 you can see here in this image.

This concludes our introduction to redox reactions, and we'll be able to learn more and more about them as we move forward in our course. So, 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 we have molecule A over here and molecule B, and they are undergoing a chemical reaction. We have these four potential answer options over here. Of course, what we need to recall from our last lesson video is that when it comes to oxidation-reduction reactions or redox reactions, all we need to remember is "Leo the lion goes ger." Remembering "Leo the lion goes ger" will help us 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 not to 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, while molecule B is gaining the electron. Hence, molecule B is reduced because it is gaining the electron, and molecule A is oxidized since it is losing the electron by the end of the reaction. We need to choose the option that corresponds with this 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. So, we can go ahead and mark A here as correct.

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.

• 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.

• 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'll discuss moving forward in our course, including cellular respiration, conduct redox reactions using electron carriers. These electron carriers are helpful to perform redox reactions. For example, NADH and FADH₂ each transport a maximum of two electrons. These carriers can shuttle electrons to different locations within a cell, kind of like an electron taxi cab.

Indeed, you can think of NADH and FADH₂ as electron taxi cabs. NAD⁺ and FAD are the oxidized forms of NADH and FADH₂ respectively. Recall that 'oxidized' corresponds to "Leo the lion goes ger," where 'Leo' represents the loss of electrons, signifying oxidation. This means that NAD⁺ and FAD will have fewer electrons; they have lost electrons compared to NADH and FADH₂. Let's take a look at our image down below to clarify this.

Notice in this image, we show an electron taxi cab. On the left-hand side, you see the empty form of the electron taxi cab. However, when this cab picks up its two passengers, these two electrons, it becomes a full taxi cab. Over here, we have the two electrons inside of this electron taxi cab. NADH forms when the oxidized form, NAD⁺, the empty taxi cab version, picks up two electrons along with a hydrogen ion, forming NADH. It is carrying these two electrons—these two passengers of the taxi cab, if you will—but it also picks up a hydrogen atom.

Looking at FAD, the empty taxi cab version of this electron carrier picks up its two passengers, these two electrons, and also two hydrogen ions, becoming FADH₂, the full cab version of this electron carrier. A helpful memory tool to remember that NADH and FADH₂ are the full taxi cab versions is to think that they are a bit heavier because they gain electrons and hydrogens. The ones with an 'H' in them are a bit heavier, indicating they are the full taxi cab versions.

Moving forward in our course on cellular respiration, you'll learn that the electrons carried by NADH and FADH₂ go to the electron transport chain, the final stage of cellular respiration. As we move forward, we will discuss more about this. For now, this concludes our brief introduction to electron carriers, NADH, and FADH₂. We'll get some practice applying the concepts we've learned as we continue our course. 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.

• 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 are fundamental to metabolic pathways and energy transfer. For example, during cellular respiration, redox reactions help convert energy stored in nutrients into ATP, the energy currency of the cell. Electron carriers like NADH and FADH₂ play a key role in these processes by transporting electrons to the electron transport chain, where ATP is produced.

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

NADH and FADH₂ function as electron carriers in cellular respiration by transporting electrons to the electron transport chain. NAD⁺ and FAD are the oxidized forms of these carriers, and they become reduced to NADH and FADH₂ by gaining electrons and hydrogen ions. These 'full' carriers then shuttle the electrons to the electron transport chain, where the electrons are used to generate ATP. Think of NADH and FADH₂ as 'electron taxi cabs' that pick up electrons and deliver them to their destination, facilitating the production of energy in the form of ATP.

What is the difference between oxidation and reduction in redox reactions?

In redox reactions, oxidation and reduction are two complementary processes. Oxidation is the loss of electrons, while reduction is the gain of electrons. These processes always occur simultaneously because when one molecule loses electrons (is oxidized), another molecule gains those electrons (is reduced). A helpful mnemonic to remember this is 'LEO the lion says GER': Losing Electrons is Oxidation (LEO), and Gaining Electrons is Reduction (GER). Understanding these concepts is essential for grasping how energy transfer and metabolic pathways function in biological systems.

Why do oxidation and reduction reactions always occur simultaneously?

Oxidation and reduction reactions always occur simultaneously because electrons cannot exist freely in a solution; they must be transferred from one molecule to another. When one molecule loses electrons (oxidation), another molecule must gain those electrons (reduction). This simultaneous occurrence ensures the conservation of charge and mass in the reaction. For example, in cellular respiration, when glucose is oxidized, oxygen is reduced, facilitating the transfer of energy and the production of ATP. This interdependence is why redox reactions are fundamental to many biological processes.

How can the mnemonic 'LEO the lion says GER' help in understanding redox reactions?

The mnemonic 'LEO the lion says GER' is a helpful tool for remembering the key concepts of redox reactions. 'LEO' stands for Losing Electrons is Oxidation, and 'GER' stands for Gaining Electrons is Reduction. This mnemonic simplifies the understanding of redox reactions by clearly distinguishing between the processes of oxidation (loss of electrons) and reduction (gain of electrons). By using this mnemonic, students can easily recall that oxidation involves the loss of electrons and reduction involves the gain of electrons, which is crucial for solving problems related to redox reactions in biological systems.