AQA A-Level Chemistry Paper 3, 2021: Question 6
13 marks · Medium difficulty · Practical Techniques & Data Analysis
Oxidation of Propan-1-ol and Yield of Propanoic Acid This question tests understanding of safe practical setup, correct reagents, and techniques involved in oxidising a primary alcohol (propan-1-ol) to a carboxylic acid (propanoic acid). It covers evaluating and correcting experimental apparatus, calculating percentage yield from mass data, and applying a test to distinguish alcohols from acids using observable results.
Practise this questionQuestion
Question text
06 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 plans to use for the experiment.
The student’s teacher says that the apparatus is not safe.
Figure 4
06.1 Give two reasons why the apparatus shown in Figure 4 is not safe.
[2 marks]
06.2 Give one additional reagent that is needed to form any propanoic acid.
[1 mark]
06.3 State two more mistakes in the way the apparatus is set up in Figure 4.
[2 marks]
06.4 State the purpose of the small glass beads in the flask in Figure 4.
[1 mark]
06.5 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.
The propanoic acid separated from the reaction mixture has a mass of 3.25 g
State the name of the technique used to separate the propanoic acid from the reaction
mixture.
Calculate the percentage yield of propanoic acid.
[4 marks]
Technique
Percentage yield
06.6 State a simple chemical test that distinguishes the propanoic acid from the
propan-1-ol.
Give one observation for the test with each substance.
[3 marks]
Test
Propanoic acid
Propan-1-ol
Section B
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Mark scheme
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Question Answers Additional comments/Guidelines Mark
6.1 M1 flask not clamped allow only the condenser is clamped 1
M2 sealed system / bung in condenser allow explanation of effect of bung being there 1
e.g. pressure build up
not reference to incorrect water direction
6.2 sulfuric acid needs adding allow hydrochloric / nitric / phosphoric 1
ignore conc/dil
not just acid/H+
6.3 M1 direction of water flow through condenser allow reference to water direction from answer to 1
6.1
allow references to safety issue(s) if not given in
6.1
M2 thermometer not needed ignore reference to position of thermometer 1
6.4 to prevent ‘bumping’ allow prevent large bubbles / ensure small 1
bubbles
not increases rate
– A-LEVEL CHEMISTRY – –
6.5 M1 (fractional) distillation 1
6.5 6.5 6.5 6.5 1
M2 mol propan-1-ol (= max mol propanoic acid) (0.108) M2 mol propan-1-ol (= max mol propanoic
60 60 60 60
acid)
6.5 x 74
M3 = 8.02 g (i.e. M2 x 74) 1
60 3.25
M3 mol propanoic acid formed
3.25 x 100 1
M4 = 40.5 %
8.02 3.25/74
M4 x100 = 40.5 %
6.5/60
6.6 M1 add sodium carbonate/hydrogencarbonate 1
M2 effervescence / bubbles not gives off (CO2) gas 1
M3 no (visible) change/reaction not nothing / no observation 1
allow acidified sodium/potassium dichromate
no visible change / stays orange
orange to green
allow named alcohol + sulfuric acid plus sweet
smell and no change/reaction
allow named carboxylic acid + sulfuric acid plus
no change/reaction and sweet smell
not pH measurement
incorrect reagent = 0/3
incomplete reagent – mark on
How to answer it
Study Guide: Investigating the Yield of Propanoic Acid
a) Apparatus Safety
Why it's unsafe:
- Flask not clamped – only the condenser is clamped, risking spillage or tipping.
- Bung in the condenser – creates a sealed system which can lead to pressure build-up when heated.
b) Reagent Required
Answer: Add a strong acid such as sulfuric acid , nitric acid or phosphoric acid .
c) Apparatus Mistakes
Two issues:
- Water should flow in at the bottom of the condenser to ensure it stays full and cools efficiently.
- Thermometer is not needed — this isn’t distillation, just heating under reflux.
d) Purpose of the Glass Beads
Answer: To prevent bumping — ensures smooth boiling and avoids sudden boiling bursts.
e) Technique and Percentage Yield
Separation technique: Fractional distillation
Calculation:
- Mol of propan-1-ol = 6.50 / 60 = 0.108 mol
- Theoretical max = 0.108 mol × 74 (Mr of propanoic acid) = 8.02 g
- Actual = 3.25 g
- Percentage yield = (3.25 / 8.02) × 100 = 40.5%
f) Chemical Test to Distinguish Acid and Alcohol
Test: Add sodium carbonate or sodium hydrogencarbonate .
Observations:
- Propanoic acid: Effervescence (CO₂ released)
- Propan-1-ol: No visible reaction
Topics
Required Practicals · Organic Chemistry · Required Practical 5: Distillation of a product from a reaction · 3.3.5 Alcohols
Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.