HIGHER GRADE CHEMISTRY CALCULATIONS

1
HIGHER GRADE CHEMISTRY CALCULATIONS

• Calculation of percentage yield.

Percentage yield is calculated using the
formula- percentage yield
x 100 The actual yield is
given in the question. The theoretical yield
is calculated from the balanced equation.
actual yield theoretical yield
Worked example. In a reaction 320 kg of sulphur
dioxide reacted with oxygen to form 360kg of
sulphur trioxide. Calculate the percentage yield.
Find the theoretical yield using the balanced
equation-
2SO2 O2 ? 2SO3
2 mol ? 2 mol
128.2 g ? 160.2 g
128.2 kg ? 160.2 kg
320 kg ? 399.9 kg
2

• Calculation of percentage yield.

• Calculations for you to try.
• 0.5 tonnes of hydrogen reacts with excess
  nitrogen to form
• 0.66 tonnes of ammonia.
• N2 3H2 ? 2NH3
• Calculate the percentage yield of
  ammonia.

N2 3H2 ? 2NH3
3 mol ? 2 mol
6 g ? 34 g
6 tonnes ? 34 tonnes
0.5 tonnes ? 2.83 tonnes
Higher Grade Chemistry
3

• Calculation of percentage yield.

Calculations for you to try. 2. Ethene
reacts with steam to ethanol C2H4
H2O ? C2H5OH Calculate the percentage
yield of ethanol when 140g of ethene
reacts to form 170 g of ethanol.
C2H4 H2O ? C2H5OH
1 mol ? 1 mol
28 g ? 46 g
140 g ? 140/28 x 46 g ?
230 g
Higher Grade Chemistry