Percentage Yield

Question

Powdered zinc metal reacts violently with sulphur (S8) when heated to produce zinc sulphide.

a)     What mass of product can be produced with 25 g of zinc?

b)     What is the actual yield if the percentage yield was 80%?

Answer 1

8Zn + S₈ ==> 8ZnS ... balanced equation

a). Assuming S8 is in excess, then the mass of product will be ...

25 g Zn x 1 mol Zn / 65 g x 8 mols ZnS / 8 mols Zn x 97 g ZnS / mol = 37 g ZnS (2 sig. figs.)

b). Percent yield = actual yield / theoretical yield (x100%)

0.80 = actual / 37 g

actual = 29.6 g = 30 g (2 sig. figs.)