A piece of solid magnesium is reacted with hydrochloric acid to form hydrogen gas:

Mg (s) + 2HCl (aq) ---> MgCl2 (aq) + H2 (g)

What volume of hydrogen gas (in mL) is collected over water at 25 degrees Celsius by reaction of 0.450 g of Mg (AW= 24.3 g/mol) with 50.0 mL of 1.0 M HCl? The barometer records an atmospheric pressure of 758 torr and the vapor pressure of water at this temperature is 23.35 torr.

1 answer

Mg + 2HCl ==> MgCl2 + H2
mols Mg = 1.00 mol
mol HCl = 0.5M

mols H2 produced from 1. mol Mg + 1 mol
mols H2 produced from 0.5 mol HCl = 1 mol
So this isn't a LR problem after all but the reactants just match. So 1 mol H2 is produced and at STP 1 mol occupies 22.4 L