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Methyl cinnamate is an ester used to add strawberry flavour to foods - Scottish Highers Chemistry - Question 3 - 2015

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Methyl cinnamate is an ester used to add strawberry flavour to foods. It is a naturally occurring ester found in the essential oil extracted from the leaves of straw... show full transcript

Worked Solution & Example Answer:Methyl cinnamate is an ester used to add strawberry flavour to foods - Scottish Highers Chemistry - Question 3 - 2015

Step 1

Complete the diagram to show an apparatus suitable for carrying out this extraction.

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Answer

To illustrate a suitable apparatus for extracting the essential oil through steam distillation, you should depict a round-bottom flask connected to a heat source, with the shredded strawberry gum leaves inside. Include a steam inlet at the top of the flask, where steam enters the mixture. The vapors of essential oil and steam should lead to a condenser, where they cool down and are collected as a liquid in a receiving flask.

Step 2

Suggest a technique that could be used to separate the mixture into pure compounds.

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Answer

The essential oil can be separated into pure compounds using fractional distillation or chromatography. Fractional distillation utilizes different boiling points of the components in the mixture, allowing them to be collected at different temperatures. Chromatography would involve passing the mixture over a medium, which separates the compounds based on their interaction with the stationary phase.

Step 3

Show, by calculation, that cinnamic acid is the limiting reactant.

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Answer

To determine if cinnamic acid is the limiting reactant, calculate the moles of each reactant:

  1. Moles of cinnamic acid = mass / molar mass = 6.5 g / 148 g/mol = 0.0439 mol.
  2. Moles of methanol = mass / molar mass = 2.0 g / 32 g/mol = 0.0625 mol.

Since the reaction requires a 1:1 ratio of cinnamic acid to methanol, and we have fewer moles of cinnamic acid compared to methanol, cinnamic acid is indeed the limiting reactant.

Step 4

Calculate the percentage yield.

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Answer

To find the percentage yield, first calculate the theoretical yield:

  1. Theoretical yield of methyl cinnamate from 0.0439 mol of cinnamic acid is:

    0.0439extmol×162extg/mol=7.1extg0.0439 ext{ mol} \times 162 ext{ g/mol} = 7.1 ext{ g}

  2. The actual yield obtained was 3.7 g. The percentage yield is calculated as follows:

    Percentage yield=(actual yieldtheoretical yield)×100=(3.77.1)×100≈52%\text{Percentage yield} = \left( \frac{\text{actual yield}}{\text{theoretical yield}} \right) \times 100 = \left( \frac{3.7}{7.1} \right) \times 100 \approx 52\%

Step 5

Calculate the cost of cinnamic acid needed to produce 100 g of methyl cinnamate.

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Answer

To produce 100 g of methyl cinnamate, we first need to find out how much cinnamic acid is required. Since the stoichiometry of the reaction is 1:1, 100 g of methyl cinnamate will require 100 g of cinnamic acid:

  1. Moles of methyl cinnamate = 100 g / 162 g/mol = 0.6173 mol.

  2. Therefore, moles of cinnamic acid needed = 0.6173 mol (same as the amount of the product).

  3. Mass of cinnamic acid required = 0.6173 mol × 148 g/mol = 91.46 g.

  4. Cost for 250 g of cinnamic acid = £35.00; hence, cost per gram = £35.00 / 250 g = £0.14.

  5. Therefore, the cost for 91.46 g:

    Cost=91.46 g×£0.14/g≈£12.80\text{Cost} = 91.46 \text{ g} \times £0.14/g \approx £12.80

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