Question

What are the oxidation number of the underlined elements in $\underset{–}{C}{H}_3\underset{–}{C}OOH$.

Answer 1

(a) By conventional method:
We will determine average oxidation number of C atom.
Let x be the oxidation number of C in $C{H}_{3}COOH$.
The oxidation numbers of H and O are +1 and -2 respectively.
$2X+4(+1)+2(-2)=0$
$x=0$
Thus, the oxidation number of both the carbon atoms is zero.

(b) According to the structure:
We will determine the oxidation number of each C atom.
(i) For C atom of -COOH group, let X be the oxidation number of this C atom.
This C is attached to one O atom by double bond, one -OH group and on methyl group. The oxidation number of O atom attached by double bond is -2. The oxidation number of -OH group is -1. The C atom of methyl group will not affect the oxidation number of -COOH group.
$x+1+1(-2)+1(-1)=0$
$x=+2$
(ii) For methyl carbon atom, let X be the oxidation number of this C atom.
This C atom is attached to 3 H atoms and one -COOH group.
The oxidation number of H atom is +1 and the -COOH group does not affect the oxidation number of C atom of methyl group.
$3(+1)+x+1(-1)=0$
$x=-2$