Understanding Redox Reactions: A Beginner's Guide

[mastiffcacher]

I know this is going to be a very simple question to ask so I hope to not bore anyone. I am having trouble with redox reactions. Not so much in completing them but in understanding them. The problem that I have is telling when something is reduced or oxidized. I know if it gains electrons, it is reduced and if it loses electrons it is oxidized. I just sometimes don't see it that way. I am working on studying metabolism and it is all redox. Can someone explain how CO is the reduced form of CO2? I see overall why it must be but cannot figure out the electrons for that reaction. It seems that almost all reaction are reduced if something is given off as products. Also, does anyone have any advice on how to tell or remember what is what?

 

[JHamm]

The best way to do these types of problems is with oxidation numbers, by definition $O$ has an oxidation number of -2 and the sums of all the oxidation numbers is equal to the net charge of the molecule; a higher oxidation number means the species has been oxidised and a lower number means it has been reduced.
In your example the oxidation number of $C$ in $CO$ is +2 whereas in $CO_2$ the oxidation number for $C$ is +4 so it has been oxidised.

 

[Borek]

In the case of CO vs CO₂ you can also think this way - to become CO₂ CO needs to react with oxygen, reaction with oxygen is - you guessed it - oxidation. Removing oxygen is reduction.

 

[mastiffcacher]

Thanks so far and I get those two points and was kind of how I can tell what their states are. I guess what I am having a hard time seeing is what the electrons are doing. All I can see is that CO is 6 electrons short when compared with CO2 which is the correct number of valence electrons. CO loses electrons and by definition should be oxidized although it has really been reduced. Why?

 

[LudusRex]

I completely understand your struggle with understanding redox reactions. Redox reactions can be complex and it takes time and practice to fully grasp them. However, I can provide some clarification and tips that may help you in your studies.

First, it is important to remember that redox reactions involve the transfer of electrons between reactants. The reactant that loses electrons is oxidized, while the reactant that gains electrons is reduced. In the case of CO2 and CO, CO2 is the oxidized form because it has more oxygen atoms than CO. CO, on the other hand, is the reduced form because it has gained electrons from CO2.

One way to remember which reactant is oxidized and which is reduced is to use the mnemonic "LEO says GER." LEO stands for "lose electrons oxidize" and GER stands for "gain electrons reduce." This can help you remember that the reactant that loses electrons is oxidized and the one that gains electrons is reduced.

Another tip is to keep track of the oxidation states of each atom in the reaction. The oxidation state is a number that represents the number of electrons that an atom has gained or lost in a reaction. In the case of CO2 and CO, carbon has an oxidation state of +4 in CO2 and +2 in CO, indicating that it has gained electrons and been reduced.

In terms of remembering which reactant is which, it may help to practice with more examples and to break down the reaction into smaller steps. For example, in the reaction between CO2 and CO, you can first identify the atoms that are being oxidized and reduced (oxygen and carbon) and then determine their oxidation states before and after the reaction. This can help you see how the transfer of electrons occurs.

I hope these tips help in your understanding of redox reactions. Remember to practice and ask for help when needed. With time and effort, you will become more comfortable with these reactions.