What is the mass of 0.5 mol of aluminum oxide? how many particles?

Given:
n (Al2O3) = 0.5 mol

To find:
m (Al2O3) -?
N (Al2O3) -?

Decision:
1) Using the periodic system of D.I.Mendeleev, calculate the molar mass of Al2O3:
M (Al2O3) = Mr (Al2O3) = Ar (Al) * N (Al) + Ar (O) * N (O) = 27 * 2 + 16 * 3 = 102 g / mol;
2) Calculate the mass of Al2O3:
m (Al2O3) = n (Al2O3) * M (Al2O3) = 0.5 * 10 ^ 2 = 51 g;
3) Calculate the number of Al2O3 molecules:
N (Al2O3) = n (Al2O3) * NA = 0.5 * 6.02 * 10 ^ 23 = 3.01 * 10 ^ 23.

Answer: The mass of Al2O3 is 51 g; the number of molecules is 3.01 * 10 ^ 23.