Calculate the mass of aluminum reacted with oxygen if 20.4 alumina was formed as a result of the reaction.

1. Let’s compose the reaction equation:

4Al + 3O2 = 2Al2O3;

2. Calculate the chemical amount of aluminum oxide:

n (Al2O3) = m (Al2O3): M (Al2O3);

M (Al2O3) = 2 * 27 + 3 * 16 = 102 g / mol;

n (Al2O3) = 20.4: 102 = 0.2 mol;

3. Determine the amount of reacting aluminum:

n (Al) = n (Al2O3) * 2 = 0.2 * 2 = 0.4 mol;

4.Calculate the mass of aluminum:

m (Al) = n (Al) * M (Al) = 0.4 * 27 = 10.8 g.

Answer: 10.8 g.