Question

3.2 g of iron is added to 50 cm3 of 1.0 mol/dm3 sulfuric acid: Fe+H2SO4= FeSO4+H2
(a): Calculate the number of moles of sulfuric acid present.
(b): Show by calculation that sulfuric acid is the limiting reactant.

Answer 1

(a) First you need to consider that the sulfuric acid you have is actually just a solution. So it contains sulfuric acid and water.

You know the concentration: c = 1.0 mol/dm3. So you have 1.0 mol H2SO4 in 1 dm3 solution. You know that you are going to use V = 50 cm3 = 0.05 dm3 of the solution. You can know calculate the amount of substance:
n (H2SO4) = c x V

(b) You can see from Fe+H2SO4= FeSO4+H2 that 1 molecule Fe is reacting with 1 molecule H2SO4. If we have a limiting reactant, this means we have less of one substance and more of the other. While all of substance 1 is already used up, we have a remainder from substance 2 which cannot react further.

So we have to find out the amounts of substance for Fe and H2SO4. We already have H2SO4 so that leaves Fe.
The molar mass M of Fe is 19 g/mol. You use the following formula to calculate it:
\[n = \frac{ m }{ M }\]