Question

Zinc reacts with 387 mL of 4.00 M cold, aque-
ous sulfuric acid through single replacement.
a. How much zinc sulfate is produced?
Answer in units of g
b. How many liters of hydrogen gas would be
released at STP?
Answer in units of L

-- I have solved part a, but I am confused on part B. I would think that since there is only 1 mol of hydrogen gas produced, that at STP, there would be 22.4 L of H2 produced, but I know that is the incorrect answer. I would know how to solve B if I knew that the original information was also at STP. Can you assume that it is?

Answer 1

I would assume that since an amount for Zn is not given that H2SO4 is the limiting reagent (LR).

Zn + H2SO4 ==> ZnSO4 + H2
You have 4.00 x 0.387 = about 1.55 mols H2SO4 which will produce 1.55 mols H2 at STP. (Note that you don't have 1 mol H2 which is the error in your thinking.)
Since 1 mol of a gas at STP occupies 22.4L, 1.55 mols will occupy 22.4 x 1.55 = ? Remember 1.55 is an estimate; you calculate should confirm that.