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?