quick chemistry question?

Question

H2 gas is produced from the single displacement reaction of magnesium with 6M HCl, with the HCl in excess. If we with to produce 42 ml of H2, how much magnesium is needed?

Answer 1

Atomic weights: Mg=24 H=1 H2=2

Mg(s) + HCl(aq) ===> H2(g) + MgCl2(aq)

42mLH2 x 1molH2/22,400mLH2 x 1molMg/1molH2 x 24gMg/1molMg = 0.0045g Mg

Assuming the 42 mL H2 isat STP, the molar volume is 22,400 mL per mole.