Question

There's reaction involving gas:

Fe + H2SO4 -> Fe2(SO4)3 + H2O + SO2

How Fe2(SO4)3 is occur? I know the "2" comes from the ion of SO4, but I don't know where the "3" comes up.

Is the Fe2(SO4)3 comes up from half-reaction method?

Is the reaction occurs in one step or multiple steps?

Please, I really need the answers :-(

Answer 1

The 3 comes from the valence of Fe, which in this case is +3, given

However, in nature, Iron reacts with dilute sulfuric acid to produce IronII sulfate and hydrogen.
In Nature, iron reacts with concentrated sulfuric acid to produced IRON II Sulfate and sulfur dioxide (and water or steam).

So my conclusion is whomever wrote the equation for you do decipher did not consider nature. The reaction should have been written this way:
Fe(s) + H2SO4(conc) -> Fe(SO4)(s) + H2O(l) + SO2)g)

Answer 2

Fe2 has oxidation number +III and (SO4)3 has ox. n -II. Its a cross rule. Now is whole molecule in electroneutral state. O has ox. number -II and and (SO4) is -II,so S has ox number VI, because4*-II (O)= -VIII + VI (S) is -II