AQA GCSE Chemistry Chemistry Paper 2 (Higher), 2023: Question 2
11 marks · Standard Demand difficulty · Short Answer
Answer questions about the energy released by burning alcohols, plot a graph of the data, and identify reactions and properties of alcohols, carboxylic acids, and carbon dioxide.
Practise this questionQuestion
Question text
02 This question is about alcohols and carboxylic acids.
Alcohols are used as fuels.
A student burned 1.00 g of six alcohols and determined the energy released
from each.
Table 2 shows the results.
Table 2
Formula of one molecule of
Alcohol Energy released in kJ/g
the alcohol
Ethanol C2H5OH 29.6
Propanol C3H7OH 33.6
Butanol C4H9OH 36.1
Pentanol C5H11OH 37.7
Hexanol C6H13OH 38.9
Heptanol C7H15OH 39.8
02.1 Calculate the mass of ethanol that must be burned to release the same amount of
energy as burning 1.00 g of heptanol.
[2 marks]
Mass = g
02.2 The energy released in kJ/g varies with the number of carbon atoms in one molecule
of each alcohol.
Plot the data from Table 2 on Figure 27.
[2 marks]
Figure 2
02.3 Estimate the energy released in kJ when 1.00 g of octanol (C8H17OH) is burned.
Use Figure 2.
[1 mark]
Energy released = kJ
Carbon dioxide is produced when alcohols are burned.
Carbon dioxide is identified by bubbling the gas through limewater.
*0072.*4 Complete the sentence.
Choose the answer from the box.
[1 mark]
calcium chloride calcium hydroxide calcium nitrate calcium sulfate
Limewater is an aqueous solution of .
02.5 Give the result of the test when carbon dioxide is bubbled through limewater.
[1 mark]
Ethanoic acid can be produced from ethanol.
02.6 What is reacted with ethanol to produce ethanoic acid?
[1 mark]
Tick ( ) one box.
A halogen
An alkali metal
An oxidising agent
Water
02.7 Ethanoic acid contains the functional group –COOH
Complete the displayed structural formula of this functional group.
[1 mark]
02.8 Ethanoic acid reacts with different compounds.
Draw one line from each compound to a product of the reaction of the compound with
ethanoic acid.
[2 marks]
Product of the reaction
Compound
with ethanoic acid
Carbon dioxide
Ethene
*09* Ethanol
Ethyl ethanoate
Sodium carbonate
Hydrogen
Poly(ethene)
Mark scheme
Show the mark scheme
Question 2
AO /
Question Answers Extra information Mark
Spec. Ref.
02.1 (mass =) AO2
39.8 1
(×1) 4.7.2.3
29.6
= 1.34 (g) allow 1.34459459 (g) correctly 1
rounded to at least 2 significant
figures
AO /
Spec. Ref.
02.2 all six points plotted correctly allow a tolerance of ± ½ a small 2 AO2
square
4.7.2.3
allow 1 mark for four or five
points plotted correctly
AO /
Spec. Ref.
02.3 40.6 (kJ) allow a value in the range 1 AO2
40.4 – 40.8 kJ 4.7.2.3
allow a value consistent with the
plotted points
AO /
Spec. Ref.
02.4 calcium hydroxide 1 AO1
4.8.2.3
AO /
Spec. Ref.
02.5 (limewater turns) milky / cloudy allow white precipitate (formed) 1 AO1
4.8.2.3
allow calcium carbonate is
produced
AO /
Spec. Ref.
02.6 an oxidising agent 1 AO1
4.7.2.3
AO /
Spec. Ref.
02.7 1 AO1
4.7.2.4
AO /
Question Answers Mark
Spec. Ref.
02.8 AO1
4.7.2.4
do not accept more than one line from a box on the left
Total Question 2 11
How to answer it
Alcohols & Carboxylic Acids: Properties and Reactions
What this question tests
This exam question assesses your understanding of organic chemistry, specifically the homologous series of alcohols and carboxylic acids. You will need to demonstrate skills in:
- Performing energy calculations from experimental data.
- Plotting and interpreting graphs accurately.
- Recalling chemical tests for carbon dioxide (limewater test).
- Identifying reactions of alcohols (oxidation to form carboxylic acids).
- Drawing displayed structural formulas of functional groups ( -COOH ).
- Predicting the products of reactions involving carboxylic acids.
Part (a) — Question 02.1
Calculating Mass from Energy Data
2 Marks📐 Step-by-Step Calculation
- Find the target energy: 1.00 g of heptanol releases 39.8 kJ of energy (from Table 2).
- Find the energy density of ethanol: 1.00 g of ethanol releases 29.6 kJ.
- Calculate the required mass: Divide the target energy by the energy released per gram of ethanol:
Mass = 39.8 / 29.6 = 1.34459... g - Round appropriately: Round to at least 2 significant figures.
Answer = 1.34 g (or 1.3 g).
❌ Common Calculation Traps
Inverting the division: Many students mistakenly calculate 29.6 / 39.8 = 0.74 g .
Sanity Check: Ethanol releases less energy per gram than heptanol (29.6 vs 39.8). Therefore, you must need more than 1.00 g of ethanol to get the same amount of energy! Your answer must be greater than 1.
• 1 Mark: Correct working shown ( 39.8 / 29.6 )
• 1 Mark: Correct final answer ( 1.34 g ). Allow rounding to at least 2 sig figs (e.g., 1.3).
Parts (b) & (c) — Questions 02.2 & 02.3
Graph Plotting and Estimation
3 Marks Total🧠 Exam Technique: Plotting Graphs
- Check the scale: On the y-axis, 10 small squares = 2 kJ/g. This means each small square represents 0.2 kJ/g.
- Plotting coordinates:
• Ethanol (2 carbons): 29.6 (2 small squares below 30)
• Propanol (3 carbons): 33.6 (2 small squares below 34)
• Butanol (4 carbons): 36.1 (half a square above 36)
• Pentanol (5 carbons): 37.7 (1.5 squares below 38)
• Hexanol (6 carbons): 38.9 (4.5 squares above 38)
• Heptanol (7 carbons): 39.8 (1 small square below 40) - Use a sharp pencil and plot with small, precise crosses ( x ).
✅ Correct Answers
02.2: All 6 points plotted correctly within ±0.5 of a small square (2 marks). 1 mark if 4 or 5 are correct.
02.3 Octanol Estimate: 40.6 kJ (1 mark).
Accept any value in the range 40.4 to 40.8 kJ, or a value consistent with your plotted curve at x = 8.
Parts (d) & (e) — Questions 02.4 & 02.5
The Limewater Test for Carbon Dioxide
2 Marks Total💡 Key Knowledge
Limewater is a common name for an aqueous solution of calcium hydroxide, Ca(OH)₂ .
When carbon dioxide gas ( CO₂ ) is bubbled through it, a chemical reaction occurs to form insoluble calcium carbonate ( CaCO₃ ), which is a white precipitate:
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
✅ Correct Answers
02.4: calcium hydroxide (1 mark)
02.5: milky or cloudy (1 mark)
Also accept: "white precipitate forms" or "calcium carbonate is produced".
Parts (f) & (g) — Questions 02.6 & 02.7
Oxidation of Alcohols & Functional Groups
2 Marks Total💡 Key Knowledge: Making Carboxylic Acids
Alcohols can be oxidized to form carboxylic acids. For example, ethanol is oxidized to ethanoic acid (the acid in vinegar).
To do this, ethanol must react with an oxidising agent (such as acidified potassium dichromate).
✏️ Drawing the Functional Group (-COOH)
Carboxylic acids contain the functional group -COOH . When drawing this, remember the valency of each atom:
- Carbon (C) must have 4 bonds.
- Oxygen (O) must have 2 bonds.
- Hydrogen (H) must have 1 bond.
How to draw it:
||
— C — O — H
Ensure you draw a double bond (=) to the top oxygen, and a single bond (-) to the oxygen of the -OH group.
• 02.6: Tick "An oxidising agent" (1 mark)
• 02.7: Correct double bond to top O and single bond to bottom O (1 mark)
Part (h) — Question 02.8
Reactions of Carboxylic Acids
2 Marks💡 Key Reactions to Memorise
1. Carboxylic Acid + Alcohol → Ester + Water
Ethanoic acid reacts with ethanol to produce the ester ethyl ethanoate.
2. Carboxylic Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
Ethanoic acid reacts with sodium carbonate to produce sodium ethanoate, water, and carbon dioxide gas (which causes fizzing!).
✅ Correct Matching Lines
- 🔹 Ethanol ───► Ethyl ethanoate
- 🔹 Sodium carbonate ───► Carbon dioxide
❌ Common Errors
Drawing too many lines: The question states "Draw one line from each compound". If you draw more than one line from a box on the left, you will lose the mark for that compound, even if one of the lines is correct!
Confusing metals with carbonates: Acids react with metals to produce hydrogen gas, but they react with carbonates to produce carbon dioxide.
Topics
Chemistry · C7: Organic Chemistry · C8: Chemical Analysis
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Higher), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.