Calculate the mass of aluminum oxide that is formed during complete combustion

Calculate the mass of aluminum oxide that is formed during complete combustion in a stream of oxygen of pure aluminum weighing 4.05 grams.

Reaction equation: 4Al + 3O2 = 2Al2O3
Let us find the amount of aluminum substance: n = m / M = 4.05 g / 27 g / mol = 0.15 mol.
According to the reaction, 2 mol of oxide is formed from 4 mol of aluminum, we will make the proportion 0.15 / 4 = n (Al2O3) / 2. Hence the amount of oxide substance n (Al2O3) = 0.15 * 2/4 = 0.075 mol.
Then the mass of the oxide: m = n * M = 0.075 mol * (27 * 2 + 16 * 3) g / mol = 7.65 g.
Answer: the mass of aluminum oxide is 7.65 g.