Question

Assign oxidation numbers to each atom in the following compounds or ions.

a) UF6
b) H2SO4
c) ClO3-

A. a) U=+6, F=-1; b) H=+1, S=+6, O=-2; c) Cl=+5, O=-2.
B. a) U=-6, F=+1; b) H=+1, S=+4, O=-2; c) Cl=+3, O=-3.
C. a) U=+6, F=-1; b) H=+1, S=+2, O=-4; c) Cl=+7, O=-1.
D. a) U=-6, F=+1; b) H=-1, S=+4, O=-2; c) Cl=+5, O=-1.

Answer 1

The correct oxidation numbers for UF6 are U=+6, F=-1. For H2SO4, they are H=+1, S=+6, O=-2. For the ion ClO3-, they are Cl=+5, O=-2, which match with option A in the question.

Step-by-step explanation:

Let's look at UF6: Fluorine (F) always has an oxidation number of -1 in compounds (rule 3). Here, there are six fluorine atoms, giving a total negative charge of -6. Since the molecule is neutral, uranium (U) must have an oxidation state of +6 to balance the -6 from the fluorine atoms: U=+6, F=-1.

In H2SO4 (sulfuric acid), hydrogen (H) typically has an oxidation number of +1, and oxygen (O) usually has -2 except in peroxides or when bonded to fluorine. Sulfur (S) must therefore have an oxidation number that balances the overall charge to zero. This gives: H=+1, S=+6, O=-2.

For the ion ClO3−, chlorine (Cl) is less electronegative than oxygen (O), so oxygen will have an oxidation number of -2, following rule 4. The sum of the oxidation numbers in the ion should equal the charge of the ion, which is -1. Therefore, Cl must have an oxidation number of +5: Cl=+5, O=-2.

The correct answers are thus: a) U=+6, F=-1; b) H=+1, S=+6, O=-2; c) Cl=+5, O=-2, corresponding to option A.