Final answer:
The mass of hydrogen gas produced from the reaction of 25 grams of aluminum with excess hydrochloric acid can be calculated by first finding the number of moles of Al, using the mole ratio from the balanced equation to find the moles of hydrogen gas produced, and finally multiplying by the molar mass of hydrogen.
Step-by-step explanation:
To calculate the mass of hydrogen gas formed when 25 grams of aluminum reacts with excess hydrochloric acid, we have to use stoichiometry to relate the mass of aluminum to the moles of hydrogen produced. Utilizing the balanced chemical equation, 2Al + 6HCl → Al₂Cl₆ + 3H₂, we can see that 2 moles of aluminum produce 3 moles of hydrogen gas. First, we need to determine the number of moles of aluminum (Al) that are in 25 grams:
Number of moles of Al = (Mass of Al) / (Molar mass of Al) = 25g / 26.98g/mol
Next, we use the mole ratio from the balanced equation to find the moles of hydrogen gas (H₂) produced from the reaction:
Moles of H₂ = (Moles of Al) × (3 moles of H₂ / 2 moles of Al)
Lastly, to find the mass of hydrogen gas, we multiply the moles by the molar mass of hydrogen (approximately 2g/mol):
Mass of H₂ = Moles of H₂ × Molar mass of H₂
Through this process, the reaction's stoichiometry helps to accurately calculate the expected mass of hydrogen gas.