Sulfuric acid is commonly used for the pickling of iron to remove surface rust before galvanisation.

$$\ce{Fe2O3 (s) + 3H2SO4 (aq) -> Fe2(SO4)3 (aq) + 3 H2O (l)}$$

However, I am not sure if given:

$$\ce{Fe2O3(s) + 3H2SO4(aq) -> ~~?}$$

how I would work this out?


You have to have an idea of the chemistry of $\ce{Fe2O3}$ and $\ce{H2SO4}$ - there is no real way around it.

The former is Fe(III) oxide - basically, a typical metal oxide. Fe(III) is a little bit oxidising, but it's not going to oxidise $\ce{H2SO4}$ (it's incredibly hard to do so).

The latter is a strong acid. It might be a little oxidising if it is concentrated, but Fe(III) isn't going to get oxidised. It can act as a dehydrating agent if it is concentrated, but there's no water to be lost.

Chances are, there's not going to be any redox reaction. It's just going to be a simple acid-base reaction to form water and a salt ($\ce{Fe2(SO4)3}$). Notice how the oxidation state of iron does not change - that lets you work out the ratio of $\ce{Fe^3+}$ to $\ce{SO4^2-}$ in the salt.


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