Question

In this chemical reaction, how many grams of Al2O3 will be produced if 375 grams of Al react completely? Express your answer to three significant figures.

Answer 1

Answer: ≈ 708 ( to 3 s.f.)

Working Out:

First we have to establish a balanced chemical equation that defines the reaction

4 Al + 3 O₂ → 2 Al₂O₃

Now, mole = mass ÷ molar mass

∴ If the mass of Al in the reaction = 375 g

then the # of moles of Al = 375 g ÷ 27 g/mol

= 13.889 mol

Also, the mole ratio between Al and Al₂O₃ is 2 : 1 (4 : 2).

As such if moles of Al = 13.889 mol

then # of moles of Al₂O₃ = 13.889 mol ÷ 2

= 6.944 mol

Since mass = mole × molar mass

Then mass of Al₂O₃ = 6.944 mol × ((27 × 2) + (16 × 3)) g/mol

= 6.944 mol × 102 g/mol

= 708.288 g