Question: how many moles of hydrogen can be produced from 8.40 g?
Answer: 8.40 g / 26.98 g per mole= 0.3113 moles of aluminum. Second, use the stoichiometric coefficients from the equation to convert moles of aluminum into moles of hydrogen. 0.467 moles of hydrogen * (1.008 g * 2) = 0.941 g of hydrogen. Hope this helps!