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Determining What is Oxidized or Reduced - Concept

Teacher/Instructor Jonathan Fong
Jonathan Fong

M.Ed.,San Francisco State Univ.

Jonathan has been teaching since 2000 and currently teaches chemistry at a top-ranked high school in San Francisco.

ÿþHere are some tips, and tricks for figuring out if something is oxidized, or reduced in a Redox reaction, or in electrochemistry.

So a mnemonic device that I teach my students that I did not make up is LEO the lion says GER. So that means that Oxidation lose electrons; LEO. Loss electrons oxidation. Then GER; gain electrons, R, reduction.

Oxidation is the loss of electrons. That also means that the oxidation number would increase. Reduction just like it says, the oxidation number would decrease. If you need help with oxidation numbers, we also have another video that will help you in figuring out oxidation numbers.

Then also in oxidation, the thing that's oxidized is also known as the reducing agent. So it's a reactant that is causing the other thing to be reduced. Just like an agent helps a ball player negotiate a contract, basically the reducing agent, is the thing that's being oxidized. It's causing the other thing to be reduced. Then also, the thing that's being reduced, is also known as the oxidizing agent.

So let's take a look, and figure out how something is oxidized or reduced. So I'll show you two methods. We have Na+Cl2 yields NaCl. This would be easy to balance, because you would put the 2 there, and a 2 there. But here is two methods that you use to figure this out.

So if we have this, we have the oxidation number of Sodium, since it's an element by itself is 0. The oxidation number of the Chlorine, since it's by itself is also 0. Then the oxidation number of Sodium on the product in the NaCl is +1. The oxidation number of Chloride is -1, because those are charges. So this is the oxidation number.

So we take a look at the Sodium, before and after, what happened to it? Well, the oxidation number went up by 1. Then we take a look at the Chlorine, what happened? Well, the oxidation number went down by 1. So what happens is, what gets oxidized? Well, the one and where the base number goes up. So that would be the Sodium in this case, Na.

Then what gets reduced? Well, that's the Chlorine would happen. So which one gained electrons? Well, the one that got reduced gained the electrons, so that would be the Chlorine. Chlorine gained electrons. Then that means that the Sodium had to lose electrons. So if you gain electrons, you lose electrons, then you can also figure that out too.

So if you have Na, then Na becomes Na+ in this reaction. Then the Cl2 becomes the Cl- in that ion. So if you take a look at what happens, well, gain of electrons, loss of electrons as well. Since I have 0charge on the left side for the Sodium, I have +1 on the right side, that means I need to add one electron here, to make the charges equal for the sodium.

So then, if you notice the electrons in your product side, so that means you're losing electrons. So that's oxidation. Then for Cl2, you balance it. So you have 2 Chlorines. So you add 2 electrons here to the reactant side. So basically you're gaining electrons, which means that you're having reduction.

So if you take a look here you can use the oxidation numbers. Or you can take a look at what's happening to the electrons like we did below, to figure out if something is being oxidized or reduced. You can do these with any Redox equation, because where there's oxidation, there always has to be reduction. You can't have oxidation and oxidation, or reduction and reduction. You have to have oxidations with reduction, because you have to have a lose of electrons, along with a gain of electrons. The electrons have to go somewhere.

So hopefully these help you figure out if something is being oxidized or reduced. Have a good one.