Question

What mass of H2 would be produced by the complete reaction of the iron bar?

Answer 1

Here the mass of iron bar and the acid used in the reaction are not given. Hence, I am assuming you using HCl and 1 g of iron bar.

The balanced equation:
2Fe(s) + 6HCl(aq) -----> 2Fe3+(aq) + 6Cl-(aq) + 3H2 (g)

Number of moles of Fe in 1g = mass/molar mass = 1g / 55.85 g/mol = 0.01791 mol

HCl is in excess and hence Fe will be the limiting reagent.

As per the balanced equation, 2 mole of Fe produces 3 moles of H2.

Thus 0.01791 mol of Fe will produce = (0.01791 mol * 3)/2 = 0.02687 mol of H2

Thus mass of 0.02687 mol of H2 = 0.02687 mol * 2.016 g/mol = 0.05417 g of H2

Now from the above model answer you may plug in any acid or any mass of iron bar and calculate the answer.