Question

Aluminium and oxygen react to produce aluminium oxide,
4 Al + 3 02 - 2 AL,O
How many kilograms of aluminium oxide are formed when 5,4 kg of aluminium react
with excess oxygen?
A 5,4 kg
B 88 kg
C 10.2 kg
D 33,6 kg

Answer 1

The balanced reaction is

4 Al + 3 O₂   →   2 Al₂O₃

so that for every 4 moles of Al and 3 moles of O2, you end up with 2 moles of Al₂O₃.

• Al has molar mass ≈ 26.982 g/mol

• O has molar mass ≈ 15.999 g/mol

• Al₂O₃ thus has molar mass ≈ 101.961 g/mol

You start with 5.4 kg = 5,400 g of Al, or

(5.4 kg Al) • (1/26.982 mol/g) ≈ 200.133 mol Al

Al₂O₃ is produced in a ratio of 2 moles to every 4 moles of Al, so you end up with about 100.067 mol Al₂O₃, which has a mass of

(100.067 mol Al₂O₃) • (101.961 g/mol) ≈ 10,202 g = 10.2 kg

so the answer is C.