What mass of zinc metal is required to evolve a #30*mL# volume of dihydrogen gas from a #30*mL# volume of hydrochloric acid at #1.00*mol*L^-1# concentration?
From the equation you can see that one mole of Zn will react with two moles of HCl.
Calculate the number of moles of HCl in 30mL of 1.00M solution, and divide by 2 for moles of Zn. Then multiply that by the molecular weight of Zn.
1M = 1mole/L 0.030L * 1mole/L = 0.030 moles HCl. 0.015 moles of Zn will react.
Each equiv of zinc metal requires 2 equiv of hydrochloric acid for complete oxidation. This gives this molar quantity: we simply take half of the molar quantity of hydrochloric acid used.
So the mass of zinc is simply: