Question

Mg + 2HCl 🡪 MgCl2 + H2

How many grams of HCl are consumed by the reaction of 2.50 moles of magnesium?
182 g HCI

What is the mass in grams of H2 gas when 4.0 moles of HCl is added to the reaction?

Answer 1

Balanced reaction: Mg + 2 HCl → MgCl2 + H2

From stoichiometry: 2 mol HCl → 1 mol H2.

If 4.0 mol HCl reacts (assume Mg is in excess or HCl is completely consumed):
- moles H2 = 4.0 mol HCl × (1 mol H2 / 2 mol HCl) = 2.0 mol H2
- mass H2 = 2.0 mol × 2.016 g/mol = 4.032 g ≈ 4.03 g

With the given 2 significant figures for 4.0 mol HCl, report mass as 4.0 g H2.