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Sucrose is a carbohydrate - Edexcel - GCSE Chemistry - Question 4 - 2022 - Paper 1

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Sucrose is a carbohydrate. When a solution of sucrose is fermented using yeast, ethanol is formed. sucrose + water → ethanol + carbon dioxide In one experiment, 1... show full transcript

Worked Solution & Example Answer:Sucrose is a carbohydrate - Edexcel - GCSE Chemistry - Question 4 - 2022 - Paper 1

Step 1

State the meanings of the terms actual yield and theoretical yield.

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Answer

The actual yield is the mass of product obtained from a reaction, determined from the experiment. In this case, it is the mass of ethanol produced, which is 8.07 g.

The theoretical yield is the maximum amount of product that could be formed from the given amounts of reactants, determined by stoichiometric calculations. For this experiment, the theoretical mass of ethanol formed is 53.80 g.

Step 2

Use the information in Figure 3 to calculate the percentage yield of ethanol in this experiment.

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Answer

The percentage yield can be calculated using the formula:

extpercentageyield=actual yieldtheoretical yield×100 ext{percentage yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100

Substituting the values from Figure 3:

ext{percentage yield} = \frac{8.07}{53.80} \times 100 \approx 15.0 \

Step 3

State two reasons why the actual yield of a reaction is usually less than the theoretical yield.

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Answer

  1. Some reactant may remain unreacted due to incomplete reactions.
  2. Side reactions could occur, leading to the formation of by-products which decrease the amount of product formed.

Step 4

Calculate the atom economy of this reaction to produce ethanol.

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Answer

The atom economy is calculated using the formula:

extatomeconomy=(molar mass of desired product(s)total molar mass of reactants)×100 ext{atom economy} = \left( \frac{\text{molar mass of desired product(s)}}{\text{total molar mass of reactants}} \right) \times 100

For the reaction, the desired product is ethanol (C₂H₅OH, molar mass = 46 g) and the total molar mass of reactants (C₁₂H₂₁O₁₁ + H₂O) is:

Total Molar Mass=342+18=360\text{Total Molar Mass} = 342 + 18 = 360

Thus, the atom economy is:

ext{atom economy} = \left( \frac{4 \times 46}{360} \right) \times 100 \approx 51.1 ext{%}

Step 5

Explain the effect on the atom economy of this reaction if the carbon dioxide produced was to make fizzy drinks.

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Answer

If the carbon dioxide produced was used to make fizzy drinks, it would be considered a useful by-product. This would enhance the atom economy because instead of being wasted, the carbon dioxide contributes to another product, thus improving the overall efficiency of the reaction. As a result, the atom economy would increase because the total molar mass of desired products would include both ethanol and carbon dioxide.

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