[Medicinal]

The sulfur content of coal can be determined by using a combustion reaction to convert sulfur to sulfur dioxide.

S(s) + O2(g) = > SO2(g)

Passing the SO2 through an aqueous solution of hydrogen peroxide, H2O2,

SO2(g) + H2O2(aq) = > H2SO4(aq)

produces sulfuric acid, which we can titrate with NaOH,

H2SO4(aq) + 2OH–(aq) < = > SO4 2–(aq) + 2H2O(l)

providing an indirect determination of sulfur.

What type of titration is this?

Strictly speacking, it's not a direct titration, or a back titration, or a displacement titration.

My best guess is it is a direct titration because S is part of the sulfuric acid. So the titrant is reacting directly with the analyte (except it isn't really at all, as SO4 is not the same as S).

I'm really confused...

Anybody know of a good analytical text that has a major emphasis on titrimetry? This is the type of analysis I like.

[Borek]

I would say direct. But don't sweat over it, such classifications are not very important.