Percentage yield and atom economy: 4.3.3 Yield and atom economy of chemical reactions: Chemistry AQA: Q&A: GCSE (9:1)

C₆H₁₂O₆ → 2CO₂ + 2C₂H₅OH
C₂H₅Br + H₂O → C₂H₅OH + HBr
C₂H₄ + H₂O → C₂H₅OH

There are 3 ways to make ethanol, C₂H₅OH. Write each one. Write the reaction that has 100% atom economy last.

it may be a slow reaction

It is not always possible to obtain 100% yield for a chemical reaction. Which of these statements is NOT a reason for not obtaining 100% yield?

75%

A reaction produces 15 grams of aspirin. If the maximum theoretical yield of aspirin was 20 grams, what is the percentage yield?

62.5 %

A reaction produces 125 grams of ammonia. If the maximum theoretical yield of ammonia is 200 grams, what is the percentage yield?

17.6 %

Hydrogen can be manufactured using the reaction between methane and steam:

CH₄(g) + H₂O(g) → 3H₂(g) + CO(g)

What is the atom economy of this reaction to 3 significant figures? (Mr: H₂ = 2, Mr: CO = 28)

51.1 %

Ethanol can be manufactured by the fermentation of glucose:

C₆H₁₂O₆ → 2CO₂ + 2C₂H₅OH

What is the atom economy of this process? (Mr CO₂ = 44, C₂H₅OH = 46, C₆H₁₂O₆ = 180)

Give your answer to 3 significant figures

1.96 g

In the preparation of copper sulfate crystals from sulfuric acid and copper oxide, the theoretical maximum mass of crystals is 2.8 grams. If the yield is 70%, what is the actual mass of crystals produced?

1.2 g

In the preparation of sodium chloride by neutralisation, the yield was 81 % and the mass of crystals obtained was 0.972 g. What was the maximum mass of crystals that could have been obtained?

it requires high temperatures and pressures

Production of glucose by reaction of ethene with steam has 100% atom economy and a 95% yield. What would be a disadvantage of producing ethanol in this way?

Find a use for the carbon dioxide as well

Production of glucose by fermentation of glucose has a relatively low atom economy:

C₆H₁₂O₆ → 2CO₂ + 2C₂H₅OH

How could the atom economy of this reaction be improved?

80 %

In the reaction to produce pure iron from iron (III) oxide by reduction with carbon monoxide:

Fe₂O₃ + 3CO → 2Fe + 3CO₂

8.96 kilograms of iron was made from 16 kilograms of iron (III) oxide. What is the percentage yield of the reaction?

65 %

In the reaction between magnesium and sulfuric acid:

Mg + H₂SO₄ → MgSO₄ + H₂

5.46 grams of magnesium sulfate (Mr = 84) was made from 2.4 grams of magnesium (Ar = 24). Calculate the percentage yield of the reaction.