Aluminum metal is reacted with oxygen gas at STP to form aluminum oxide. If 168.6 grams of aluminum are reacted, what is the number of grams of aluminum oxide produced?

Answer 1

First, write the correctly balanced equation:

4Al(s) + 3O₂(g) ===> 2Al₂O₃(s)

Next, find moles of Al used in the reaction:

168.6 g Al x 1 mol Al/26.98 g = 6.249 moles Al

Next, find moles of Al₂O₃ produced from this many moles of Al. You do this using the mole ratio in the equation:

6.249 moles Al x 2 moles Al₂O₃/4 moles Al = 3.1245 moles Al₂O₃ formed >> (this assumes O₂ is not limiting)

Finally, convert this to grams of Al2O3, and correct for significant figures:

3.1245 moles Al₂O₃ x 101.96 g/mole = 318.6 g (to 4 sig. figs.)