Determining the Mass of a Product of a Gas Phase Reaction

Question

How many grams of iron are needed to produce 11.7 L of hydrogen gas according to the following reaction at 25 °C and 1 atm? 

iron (s) + hydrochloric acid(aq)  iron(II) chloride  (aq) + hydrogen (g)

? g iron

Answer 1

Fe(s) + 2HCl(aq) ===> FeCl₂(aq) + H₂(g) ... balanced equation

iron + hydrochloric acid = iron(II)chloride + hydrogen gas

25ºC + 273 = 298K = temperature

1 atm = pressure

From PV = nRT we can convert 11.7 L of H₂ gas to moles of H₂ gas and then from that, we can find moles of Fe needed to produce that, and finally convert moles Fe to grams Fe.

n = PV/RT = (1atm)(11.7 L)/(0.0821)(298) = 0.4782 moles H₂ gas

0.4782 mol H₂ x 1 mole Fe/1 mol H₂ = 0.4782 moles Fe

0.4782 mol Fe x 55.85 g Fe/mol Fe = 26.7 g Fe needed (to 3 significant figures)