Question

What mass of hydrogen gas is produced when a 7.43 g chunk of zinc dissolves in 500.0 mL of 1.200M HCl?

Answer 1

This is a limiting reagent (LR) problem. You know that when an amount for BOTH reactants is given.
Zn + 2HCl ==> H2 + ZnCl2

mols Zn = grams/molar mass.
mols HCl = M x L = ?

Using the coefficients in the balanced equation, convert mols Zn to mols H2.
Do the same for mols HCl to mols H2.
It is likely that the two values for mols Zn will not agree which means one of them is wrong; the correct value in LR problems is ALWAYS the smaller value and the reagent producing that value is the LR.
Using the smaller value of mols H2, convert to grams. g = mols x molar mass.

Answer 2

For my problem, grams of Zn = 7.77

Zn(s) + 2HCl(aq) --> H2(g) + ZnCl2(aq)

1.2 M HCl = x/0.5 L. x = 0.6 mol HCl
7.77g / 65.38 (molar mass) = 0.1188 mol Zn

mols Zn -> H2
0.1188 * (1/1) = 0.1188

mols HCl -> H2
0.6 * (1/2) = 0.3

0.1188 * 2.02(molar mass of H2) =

0.239976 g