Question

What are the oxidation states of carbon in acetic acid?

Answer 1

Oxidation states don't really mean much in covalent compounds like acetic acid. In here, there are two different carbons, each with their own oxidation state.

If you want to just do it, then assume `"C"_2"H"_3"O"_2^(-)` has two equivalent carbons (which is not true):

`[stackrel(0)("C"_2)stackrel(+1)("H"_3)stackrel(-2)("O"_2)]^(-)`

Then you should find that the two carbons' oxidation states must somehow add to be `0`. So, treat each carbon fragment separately, as the carbons are NOT equivalent:

`stackrel(+1)("H"_3)stackrel(color(blue)(-3))("C")-`

`-stackrel(color(blue)(+3))("C")stackrel(-2)("O")stackrel(-2)("O")stackrel(+1)("H")`

And so we still have `-3 + 3 = 0` for the combined oxidation state as in our initial assumption.

Answer 2

Here the two possible structural formula have been derived from given molecular formula `C_2H_4 O_2`.
Oxidation states (os) of different elements have been shown in the figure.
The oxidation states of different atoms in the covalent compound are calculated on the basis of the assumption that the molecule is an aggregate of ions and gain and loss of electron/s between bonded atoms occur depending on their electronegativity difference.

In acetic acid
C-atom of >C=O group gives two e to one O atom linked with it through double bond and also gives one e to the O atom of -OH group linked with it with through single bond and no electron is gained from C atom linked with it. So net loss of e is 3 and OS of it becomes +3.

But in `CH_3` group of acetic acid C-atoms takes 3 e from 3 H-atoms and no e from C-atom linked with it.Hence it acquires -3 OS here.

Similarly we can calculate the oxidation states of different atoms in the Glycolaldehyde molecule (having molecular formula `C_2H_4 O_2`).considering the differences in electronegativities of atoms linked.