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Year 11
AQA
Foundation

Percentage yield and atom economy

I can perform calculations related to various aspects of industrial processes, and explain decision-making about the chosen reaction pathways in those processes.

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New
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Year 11
AQA
Foundation

Percentage yield and atom economy

I can perform calculations related to various aspects of industrial processes, and explain decision-making about the chosen reaction pathways in those processes.

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Lesson details

Key learning points

  1. In an ideal chemical reaction, all atoms in the reactants would end up in useful products, with no waste.
  2. The theoretical yield of a chemical reaction can be calculated from the reaction equation alone.
  3. The percentage yield shows how actual yield compares with theoretical yield.
  4. Atom economy is a measure of the efficiency with which a reaction uses its reactants.
  5. Many factors will be considered when choosing a reaction pathway.

Keywords

  • Theoretical yield - is the maximum calculated mass of product expected to form from a given mass of reactants

  • Actual yield - is the actual amount of product obtained from a chemical reaction

  • Percentage yield - is the actual yield (mass of product obtained) divided by the theoretical yield (maximum mass of product possible), as a percentage

  • Atom economy - is the percentage, by relative mass, of reactants that are converted into useful products

  • Useful product - is a chemical product that is desired or valuable

Common misconception

Pupils often confuse percentage yield with atom economy, thinking both measure the same efficiency aspect.

Clarify that percentage yield measures actual vs. theoretical product amount, while atom economy measures reactants' mass converted to desired product.

Use real-world examples to differentiate concepts, such as pharmaceutical synthesis, to show practical importance of both percentage yield and atom economy in industry.
Teacher tip

Equipment

None required.

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Three beads are red and seven beads are green. What percentage of the beads are green?
Correct Answer: 70%, 70
Q2.
Balance the following chemical equation: CH₄ + O₂ → H₂O + CO₂
Correct answer: CH₄ + 2O₂ → 2H₂O + CO₂
2CH₄ + O₂ → 2H₂O + CO₂
2CH₄ + O₂ → H₂O + 2CO₂
CH₄ + 2O₂ → H₂O + CO₂
Q3.
Calculate the relative formula mass (Mr) of calcium carbonate, CaCO₃. Relative atomic masses (Ar): Ca = 40; C = 12; O = 16.
Correct Answer: 100
Q4.
Which of the following statements about the equation below are correct? 2Mg + O₂ → 2MgO
Correct answer: The ratio of magnesium to magnesium oxide is 1 : 1
The ratio of magnesium oxide to oxygen is 1 : 2
Correct answer: The ratio of oxygen to magnesium is 1 : 2
The ratio of oxygen to magnesium oxide is 2 : 1
Q5.
When magnesium reacts with oxygen in the air to form magnesium oxide, magnesium is the limiting factor. There is more oxygen present than is needed, so we say that the oxygen is in .
Correct Answer: excess
Q6.
Calculate the mass of 0.5 mol of magnesium. Give your answer to 2 s.f. Relative atomic mass (Ar) of Mg = 24.
Correct Answer: 12 g, 12

Exit quiz

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6 Questions

Q1.
Match the following terms to the correct definitions.
Correct Answer:theoretical yield,Maximum calculated mass of product expected to form in a reaction.

Maximum calculated mass of product expected to form in a reaction.

Correct Answer:actual yield,Amount of product obtained from a chemical reaction.

Amount of product obtained from a chemical reaction.

Correct Answer:atom economy,Percentage of reactants converted into useful products.

Percentage of reactants converted into useful products.

Q2.
During an experiment, a pupil produces 3.25 g of magnesium oxide. The theoretical yield of magnesium oxide is 4.00 g. Calculate the percentage yield. Give your answer to 3 s.f.
Correct Answer: 81.3%, 81.3
Q3.
Why might the percentage yield of a reaction not be 100%?
Correct answer: The reaction is reversible.
The reaction goes to completion.
Correct answer: Product may be lost during transfer.
All the reactants are used in the reaction.
Q4.
Calculate the theoretical yield of magnesium oxide when 2.40 g of magnesium reacts with excess oxygen. Give your answer to 3 s.f. 2Mg + O₂ → 2MgO Relative atomic masses (Ar): Mg = 24; O = 16.
Correct Answer: 4.00 g, 4.00g, 4.00
Q5.
Which of the following statements about atom economy are correct?
Correct answer: It is a measure of the efficiency of how a reaction uses its reactants.
It shows how actual yield compares to theoretical yield.
It assumes the reaction is not complete.
Correct answer: It assumes no side reactions occur.
Q6.
Calculate the percentage atom economy of the reaction below, when hydrogen is the useful product. Give your answer to 3 s.f. 2H₂O → O₂ + 2H₂ Relative atomic masses (Ar): H = 1; O = 16.
Correct Answer: 11.1%, 11.1