A student plans an experiment to investigate the yield of propanoic acid when a sample of propan-1-ol is oxidised - AQA - A-Level Chemistry - Question 6 - 2021 - Paper 3
Question 6
A student plans an experiment to investigate the yield of propanoic acid when a sample of propan-1-ol is oxidised.
Figure 4 shows the apparatus that the student pla... show full transcript
Worked Solution & Example Answer:A student plans an experiment to investigate the yield of propanoic acid when a sample of propan-1-ol is oxidised - AQA - A-Level Chemistry - Question 6 - 2021 - Paper 3
Step 1
1. Give two reasons why the apparatus shown in Figure 4 is not safe.
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Answer
The flask is not clamped, which could lead to it falling and causing breakage.
The system is not sealed properly, which can result in pressure build-up and potential leaks.
Step 2
2. Give one additional reagent that is needed to form any propanoic acid.
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Sulfuric acid needs to be added to facilitate the oxidation process.
Step 3
3. State two more mistakes in the way the apparatus is set up in Figure 4.
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The direction of water flow through the condenser is incorrect and should be reversed to ensure effective cooling.
A thermometer is not needed in the setup as it doesn't contribute to the reaction.
Step 4
4. State the purpose of the small glass beads in the flask in Figure 4.
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The small glass beads are used to prevent 'bumping' by providing surface area for condensation.
Step 5
5. After correcting the mistakes, the student heats a reaction mixture containing 6.50 g of propan-1-ol with an excess of the oxidising agent. State the name of the technique used to separate the propanoic acid from the reaction mixture. Calculate the percentage yield of propanoic acid.
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Technique: Fractional distillation.
To calculate the percentage yield:
Mass of propan-1-ol = 6.50 g
Molar mass of propan-1-ol = 60.1 g/mol (1 mol propan-1-ol produces 1 mol propanoic acid)
Moles of propan-1-ol used = 6.50 g / 60.1 g/mol ≈ 0.108 mol
Theoretical yield of propanoic acid = 0.108 mol × 74.1 g/mol ≈ 8.0 g
