How many moles of Aluminum are needed to form 3.7 moles Al2O3?

Question

4 Al + 3 O2 ----> 2 Al2O3

Answer 1

This is a stoichiometry problem that requires the use of mole ratio from the balanced equation.

3.7 moles Al2O3 * (4mol Al/ 2 mol of Al2O3)= 7.4 moles Al.

The mole ratio 4/2 is used because those are the coefficients of the balanced equation indicating that for every 4 mol of Al, 2 mol of Al2O3 is being produced.

Notice that the units of mol Al2O3 cancels out leaving with moles of Al. You can use the mole ratio of any balanced equation to find the moles of any reactant and product in the equation.