Question

Determine the oxidation number (oxidation state) for the indicated element in each of the following compounds.

A: Ti in TiO2

B: Al in NaAlH4

C: C in C2O42?

D: N in N2H4

E: N in HNO2

F: Sn in SnCl3?

Answer 1

A)  TiO2 = 0
x + (-2*2)= 0
x - 4 = 0 NOTE that in most compounds oxidation number of oxygen is negative 2.
so, x = +4
the oxidation number of titanium in TiO2 is +4

B )Na + Al +4(H) = 0 (where Na. Al, and H are the oxidation numbers of Na, Al, and H.) We use the rules to assign oxidation numbers of +1 to Na and -1 to H (be sure you understand this!!). We have 1 + Al +4(-1) = 0, and Al = +3.

C)  always has an oxidation states of -2.

so if there are 4 O atoms, with -2 each, it gives a total of -8

since the charge on the ion is -2, the total carbon is +6, and there are 2, so each carbon is +3

C= +3

D) Consider the structural formula of N2H4 as well as each element's electro-negativity:
EN of N = 3.04
EN of H = 2.20

In the lewis dot-diagram or the structural formula of N2H4, each nitrogen atom is surrounded by two hydrogen atoms,
each of these hydrogen atoms will form a covalent bond with a nitrogen atom.
Covalent bonds are treated as ionic bonds when concerning oxidation:
the more electronegative atom (we say) will take the electron(s).

H being less electronegative will lose its electron to N.
The charge on H will be +1, as will its oxidation number/state.

Now we can calculate the oxidation number/state of N:

Since this molecule is neutral, we assume the O.S. will equal to 0.
Let x be the O.S. of N.
(+1)(4) + (2)(x) = 0
+4 + 2x = 0
2x = -4
x = = -4/2
x= -2

Therefore the O.S. of N in N2H4 is -2.

E) Oxidation state of H = +1
Oxidation state of O = -2

since there are two oxygen in the molecule so total charge due to O is = -4

as the molecule is neutral (total charge =0)

Therefore

+1 due to H and -4 due to oxygen makes N to have in +3 oxidation state.

That is your answer. N has oxidation number = +3 here.

F) I assume the negative sign you are showing is for the whole thing. If so the Sn must be +2.

Chloride ions are -1 when combined with metals, so since there are three of them, the Sn must be +2 to have a minus 1 leftover.

But if you are asking just about neutral SnCl3 then the Sn has to be +3.