If 6.5g of magnesium ribbon reacts completely with Hydrochloric acid, how many grams of hydrogen gas would be…

Analyze the question: We need the mass of H₂ produced when 6.5 g of Mg reacts completely with HCl. This is a reacting-mass (stoichiometry) problem.

Concept: From the balanced equation, the mole ratio decides how much product forms:

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

1 mole of Mg gives 1 mole of H₂.

Solution:

1. Molar mass of Mg = 24.0 g/mol
2. Moles of Mg = 6.5 / 24.0 = 0.2708 mol
3. Mole ratio Mg : H₂ = 1 : 1, so moles of H₂ = 0.2708 mol
4. Molar mass of H₂ = 2 × 1.0 = 2.0 g/mol
5. Mass of H₂ = 0.2708 × 2.0 = 0.5417 g ≈ 0.54 g

Shortcut: 24 g Mg gives 2 g H₂, so 6.5 g gives (6.5 × 2) / 24 = 13/24 ≈ 0.54 g.

54 g).

Tip: In reacting-mass questions, follow this sequence: balance the equation, convert mass to moles, apply the mole ratio, then convert back to mass. Watch out for H₂ having a molar mass of 2, not 1. Using 1 would give 0.27 g, a common trap.