Redox Question help

[john216]

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I know how to rules of assigning oxidation numbers but I just don't get them when they are in reaction

ex . C5H12 + 8 O2 -> 5 CO2 + 6 H2O


Here, if you were to find oxidation # of oxygen on both left and right sides

So on left, O2 is elemental form, it would be 0 e-.

But on right, as you see, there are oxygens present in both CO2 and H2O having oxidation # of 2e- on both.

do you just add those up to 4 e-?

so the total # of electrons are going from 0e- to 4 e-?

Is this right?

 

[sylviej]

Umm. I think you mixed up some concepts here. Oxidation number refer to the indicator of the degree of oxidation of an atom in one compound. the oxidation numbers are not associated with electrons(if you're only trying to figure out the oxidation number). On the left side, since oxygen is in element form, yes the oxidation number is 0 (not 0 e-). on the right side, the oxidation number for O in CO2 is -2 and the oxidation number for O in H2O is -2. you can't add them up and say the total oxidation number is -4.

If you are talking about the electron transferred from reactants to products, that's another case though.

Hope this helps...

 

[john216]

thanks,, then
If you were to look at how many electrons transferred,

What is oxidized by how many electrons ?
, and what is reduced by how many electrons ?

Thank you

 

[sylviej]

thanks,, then
If you were to look at how many electrons transferred,

What is oxidized by how many electrons ?
, and what is reduced by how many electrons ?

Thank you

Um… I think the electron transfer problem is more discussed in elements involving ionic bonds. I don't think there is any electron transferred here although it is indeed a redox reaction. Since this is covalent bonding, the oxidation sate of carbon can be very difficult to deal with in the first place. If you would look at C5H12, what would you say is the oxidation state of H? and what about C? See, my point is, if H is considered to be "acting normal", then it should have an oxidation state of +1, but now, if H is +1, C should be negative. Therefore this is very problematic. Organic redox reaction are very different compared to redox reaction of the inorganic compounds.

Maybe this can help you out a little more http://en.wikipedia.org/wiki/Organic_reduction

🙂