Question

What mass of H2 forms when

35.25 g of Al reacts with excess
hydrochloric acid?
2AI+ 6HCI→ 2AlCl3 + 3H₂
Al: 26.98 g/mol
H₂: 2.02 g/mol
[?] g H₂

Answer 1

1) Find number of moles of Al reacted:
35.25/26.98 (mass reacted/molar mass of Al)

2) Find number of moles of H2 produced:
Number of mol. of Al x 3/2 (based on stoichiometry)

3) Find mass of H2 formed:
Number of mol. of H2 x molar mass of H2 = 3.9588mol = 4 mol (estimated value)