Mixed Stoichiometry

Question

How many liters of hydrogen gas at STP can be generated from the reaction of excess hydrogen chloride with 14.5 g of aluminum?

Does this answer require scientific notation?

Answer 1

Write the balanced equation so you can see the relationship between moles Al and moles H₂.

2Al + 6HCl ==> 2AlCl₃ + 3H₂(g) ... balanced equation - shows 2 mol Al -> 3 mol H₂

moles Al = 14.5 g x 1 mol Al/26.98 g = 0.5374 moles Al

moles H2 produced: 0.5374 mol Al x 3 mol H₂ / 2 mol Al = 0.8062 moles H₂

Volume H₂ @ STP (recall that at STP 1 mol of ideal gas = 22.4 L)

0.8062 moles H₂ x 22.4 L / mol = 18.1 liters (this does not require scientific notation; however it could be expressed in scientific notation as 1.81x10¹ liters)