# Chemistry help! (Amount of substances A - level OCR)

Hi can anyone please walk through this question?

What is the percentage yield when 20 g of aluminium are produced from 50 g of aluminium oxide?
2Al2O3 4Al + 3O2

Thank you.
so 50g of Al2O3 gives 50/(27X2+16X3) = 0.4902 moles
20g of Al gives 20/27 = 0.7407 moles
mole ratio of Al2O3:Al = 2:4 =1:2
so you would expect 0.4902x2 = 0.9804 moles of Al to be produced from 50g of Al2O3
the % yield = actual mole of Al produced/expected mole of Al x100%
= 0.7407/0.9804 x100%
=75.6%
Original post by Hiruja
Hi can anyone please walk through this question?

What is the percentage yield when 20 g of aluminium are produced from 50 g of aluminium oxide?
2Al2O3 4Al + 3O2

Thank you.

Hey, just to summarize this, in order to find the percentage yield of a chemical reaction, you need to compare the actual yield (the amount of product obtained in the experiment) with the theoretical yield (the maximum amount of product that could be obtained according to stoichiometry).
Thank you!