How many grammes of zinc metal are required to produce 10.0 litres of hydrogen gas, at 25 Celsius and 1.00 atm pressure, by reaction with excess hydrochloric acid? Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g) ?
So, you have your balanced chemical equation
Use the ideal gas law equation,
Automatically, this also be the number of moles of zinc that reacted
Now just use zinc's molar mass to determine the exact mass