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Grade 11 Chemistry Percentage Yield Problems/Solutions
Grade 11 Chemistry Percentage Yield Problems/Solutions
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Percentage Yields Problems1. 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?
Unknown: mass of zinc sulphide
Given: mass of zinc metal = 25 g
Molar mass of zinc = 65.38 g/mol
Grams to moles:
25 g ZnS / 65.38 g/mol = 0.382 mol
0.382 mol Zn ÷ 1 mol Zn x 1 mol ZnS = 0.382 mol ZnS
Moles to grams:
0.382 mol ZnS x 97.446 g/mol = 37.22 g
∴ 37.22 g ZnS can be produced by 25 g of Zn.
b. What is the actual yield if the percentage yield was 80%?
Actual yield = (Percentage yield x Theoretical yield) / 100
= ( 80 x 37.22 ) / 100
, = 29.78 g
∴ 29.78 g ZnS was obtained (actual yield).
2. When 9 g of hydrogen reacts with oxygen, 73 g of water is produced.
a. What is the theoretical yield of water?
2 H₂ + O₂ → 2 H₂O
Theoretical yield = 9 g H₂ / MM[H₂]
= 9 g / 2.016
= 4.46 mol H₂
4.46 mol H₂ x 1 mol H₂ / 1 mol H₂O
= 4.46 mol H₂O
4.46 mol H₂O x 18.015 g/mol H₂O
= 80.35 g H₂O
∴ 80.35 g H₂O is the theoretical yield.
b. What is the actual yield?
Actual yield = 73 g
∴ 73 g H₂O is the actual yield.
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