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oxidation numbers

 
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drgshahbaz1193



Joined: 26 Mar 2010
Posts: 18
PostPosted: Sun May 02, 2010 4:32 pm    Post subject: oxidation numbers Reply with quote
I am having a problem with the concept of oxidation numbers. What do they really represent? I mean sometimes an actual oxidation and reduction reactions where electrons are physically lost do not occur. There is just an unequal sharing of electrons.

Also how is the oxidation number of a molecule related to its charge?

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mcat_premed3832



Joined: 19 Oct 2006
Posts: 412
PostPosted: Mon May 03, 2010 12:38 am    Post subject: Reply with quote
Quote:
I am having a problem with the concept of oxidation numbers. What do they really represent? I mean sometimes an actual oxidation and reduction reactions where electrons are physically lost do not occur. There is just an unequal sharing of electrons.


Just to be clear: I would guess that 95% of students who always score perfect on MCAT oxidation number questions don't have a clear idea as to what oxidation numbers represent. They can usually give the classic definition: oxidation numbers are a form of electron bookkeeping.

In fact, oxidation numbers and oxidation state are not technically the same. BUT, for MCAT purposes, they are identical! Another strange fact is that oxidation numbers are particularly helpful in coordination chemistry and for balancing reactions: neither of which are necessary for the MCAT (to be clear, you might need to balance a rather easy chemical equation but you won't need to use oxidation numbers to do it on the MCAT).

So basically, if you follow the rules, you will get all the questions correct for the MCAT. Even though, you will not be asked to put that knowledge into a practical application (ie. coordination chemistry or balancing a redox reaction).

Quote:
Also how is the oxidation number of a molecule related to its charge?


The oxidation numbers of individual atoms sum to the oxidation state of the molecule.
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