[Mr. Raru]

Is it true that sulfide is oxidized to sulfate while H₂S is oxidized to S₈? Why is this so when both have an oxidation number of 2 to begin with?

[Mitch]

In what reaction?

[Mr. Raru]

A solution of copper(II) sulfide is oxidized by dilute nitric acid.

[Alberto_Kravina]

Hmmm...solution of copper sulfide? copper sulfide has apretty low solubility product (Ksp(CuS) = 1.3×10^{-3 6})
Sulfide is partially oxidized to sulfate with dil. nitric acid.

H₂S is oxidized to S₈ with oxygen:

8 H₂S + 4 O₂ ----> S₈ + 8 H₂O

Why is this so when both have an oxidation number of 2 to begin with?

I don't know if I understood the question, but I think that it depends on the strength of the oxidation agent.