Determine the oxidation number of Sulpher in SO3-2.?

Question

Determine the oxidation number of Sulpher in SO3-2.

Answer 1

Same answer, different setup.  We know that the sum of the oxidation numbers is zero for a compound and the ionic charge for a polyatomic ion, and we know that sulfite ion is -2.

Create an algebraic equation by multiplying the subscripts times the oxidation number of a single element.

+x -6 = -2

+x -2

S O3

Solve for x

x = +4

Answer 2

O is -2, so that leads to a total of 3×-2=-6

total: -2

total from atoms: S -6 = -2

S = -2+6 = +4