Oxidation Number

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Mrudula Akkinepally
Posts: 105
Joined: Wed Sep 30, 2020 9:31 pm

Oxidation Number

Postby Mrudula Akkinepally » Sat Nov 14, 2020 9:28 pm

Can someone explain to me how to calculate the oxidation number and what it means?

Claire_Latendresse_1E
Posts: 130
Joined: Wed Sep 30, 2020 9:37 pm
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Re: Oxidation Number

Postby Claire_Latendresse_1E » Sat Nov 14, 2020 9:41 pm

Hi! There are a few rules that are good to know. I attached a photo with the rules that I use.
Here's an example of how I work through an oxidation number problem (I hope it works for you):
For CO2, I know that oxygen's oxidation number is -2 (the fifth rule in the picture). Because there are two oxygens, the oxygens contribute a total charge of -4 to the molecule.
Because the molecule is not an ion, I know that the net charge must be 0. So, carbon must have an oxidation number of +4 in order to cancel out the oxygen's charge of -4 (0 = x - 4, so x=4).
Here's how I would go through an oxidation number problem with an ion:
For NH4(+), I know that hydrogen's oxidation number is always +1 (the first rule in the picture). Because there are four hydrogens, they contribute a total charge of +4 to the ion.
The ion has a charge of +1, so carbon must have a charge of -3 to bring down the hydrogen's charge of +4 (1=x+4, so x= -3).
I hope this helps!
Attachments
unnamed.jpg

Tanya Nguyen 1B
Posts: 91
Joined: Wed Sep 30, 2020 9:33 pm

Re: Oxidation Number

Postby Tanya Nguyen 1B » Sat Nov 14, 2020 9:49 pm

Oxidation numbers tell you of electrons are lost or gained. The chart posted above is a good reference. For neutral compounds (no charge) all the oxidation numbers should add up to 0. For ions, all the oxidation numbers should add up to the charge of the ion. Then for free elements its oxidation number is 0.

Mrudula Akkinepally
Posts: 105
Joined: Wed Sep 30, 2020 9:31 pm

Re: Oxidation Number

Postby Mrudula Akkinepally » Sat Nov 14, 2020 10:48 pm

That helps a lot, thank you !

David He
Posts: 49
Joined: Wed Oct 07, 2020 12:16 am
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Re: Oxidation Number

Postby David He » Sun Nov 15, 2020 11:18 am

In the sampling question you can click "hint" on the top then you will get a link to explanation!


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