Edexcel A-Level Chemistry AS Paper 2, June 2023: Question 7

13 marks · Hard difficulty · Synoptic Questions

Assess the properties, reactions, oxidation, and preparation of the primary alcohol butan-1-ol including intermolecular forces, enthalpy level diagram, functional group tests, and synthesis techniques.

Practise this question

Question

Question text

7 This question is about the primary alcohol butan‑1‑ol.

(a) Which are the intermolecular force(s) between butan‑1‑ol molecules in the

liquid phase?

(1)

A hydrogen bonding only

B hydrogen bonding and permanent dipole‑dipole forces only

C hydrogen bonding, permanent dipole‑dipole forces and London forces

D London forces only

(b) The equation for the complete combustion of butan‑1‑ol is shown.

CH CH CH CH OH(l) + 6O (g) → 4CO (g) + 5H O(l) Δ H d = –2675.6 kJ mol–1

32 2 2 2 2 2 c

Draw a labelled enthalpy level diagram for this reaction, using the axes provided.

You may use the labels ‘reactants’ and ‘products’ in place of the formulae shown in

the equation.

(2)

Enthalpy

Progress of reaction

(i) Which is a suitable test and result for butan‑1‑ol?

(1)

Test reagent Observation

A phosphorus(V) chloride PCl5(s) white smoke

B phosphorus(V) chloride PCl5(s) steamy fumes

C sodium carbonate Na2CO3(aq) carbon dioxide given off

D sodium carbonate Na2CO3(aq) effervescence

22 (ii) State how to produce butanal in high yield when butan‑1‑ol reacts

with acidified potassium dichromate(VI).*P71927A02228*

(1)

(iii) Describe a chemical test, including the expected results, that would confirm

the presence of an aldehyde such as butanal.

(2)

*(iv) Describe, including practical details, how a sample of

butanoic acid (boiling temperature 166°C) could be prepared from

butan‑1‑ol (boiling temperature 117°C) using

acidified potassium dichromate(VI).

Include labelled diagrams of the apparatus you would use for the reaction,

and for collecting the product.

You may assume that all necessary safety precautions are observed.

(6)

*P71927A02328*

… 24

… *P71927A02428*

(Total for Question 7 = 13 marks)

Mark scheme

Show the mark scheme

Question

Answer Mark

Number

7(a) The only correct answer is C (hydrogen bonding, permanent dipole-dipole forces and London forces) (1)

A is not correct because although hydrogen bonding is the strongest intermolecular force, permanent dipole-dipole

interactions and London forces are also present

B is not correct because London forces are always present between molecules in the liquid state

D is not correct because London forces are the weakest of the intermolecular forces, and other intermolecular forces are

also present between butan-1-ol molecules

Question

Acceptable Answer Additional Guidance Mark

Number

7(b) Example of enthalpy level diagram (2)

• reactants above products (1)

H⊖

Allow ‘reactants’ & ‘products’ OR chemical formulae correctly

balanced (with/without states) on levels

• downwards pointing arrow from reactants to Arrow label = H / H / −2675.6 kJ mol−1

r c

products Allow label of just ‘enthalpy change’ / H / Hc

and

label on down arrow (1) Arrow must go from level to level without any gap(s)

Ignore activation energy ‘hump’ if reaction profile diagram drawn

Do not award double headed arrow for downwards pointing arrow

Question

Answer Mark

Number

7(c)(i) The only correct answer is B (phosphorus(V) chloride PCl5(s) steamy fumes) (1)

A is not correct because hydrogen chloride is not white smoke

C is not correct because carbonates only react with acids and CO2 cannot be observed

D is not correct because carbonates only react with acids

Question

Acceptable Answer Additional Guidance Mark

Number

7(c)(ii) An answer that makes reference to the following point: (1)

• set equipment for distillation (rather than reflux) / distil out the Allow just ‘distillation’/’distil’

aldehyde as soon as it is formed Allow (use) stoichiometric quantities (for partial

oxidation)

Allow a form of words to mean the same as

stoichiometric

Question

Acceptable Answer Additional Guidance Mark

Number

7(c)(iii) An answer that makes reference to the following points: (2)

• (react with) Benedict’s / Fehling’s solution (1) Allow Tollens’ reagent (M1)

and and

heat / warm heat / warm

Aldehyde gives a silver mirror (M2)

• butanal gives a red/brown ppt (butan-1-ol does not (1) Allow solid for ppt

react)

Ignore ‘starting’ colour even if incorrect

Allow Schiff’s reagent test (M1)

aldehydes give a magenta/red/pink colouration (M2)

Ignore use of 2,4-DNPH (aldehydes give

yellow/red/orange ppt)

Check for missing ‘heat/warm’ and ‘ppt’

Question

Acceptable Answer Additional Guidance Mar

Number

*7(c)(iv) This question assesses a student’s ability to show a coherent and Guidance on how the mark scheme should be applied: (6)

logically structured answer with linkages and fully-sustained reasoning.

Marks are awarded for indicative content and for how the answer is The mark for indicative content should be added to the mark for lines of reasoning. For

structured and shows lines of reasoning. example, an answer with five indicative marking points that is partially structured with

The following table shows how the marks should be awarded for some linkages and lines of reasoning, scores 4 marks (3 marks for indicative content and

indicative content. 1 mark for partial structure and some linkages and lines of reasoning).

Number of indicative marking Number of marks awarded for

points seen in answer indicative marking points If there are no linkages between points, the same five indicative marking points would

64 yield an overall score of 3 marks (3 marks for indicative content and no marks for

5-4 3 linkages).

3-2 2

11 In general it would be expected that 5 or 6 indicative points would get 2 reasoning

00 marks, and 3 or 4 indicative points would get 1 mark for reasoning, and 0, 1 or 2

The following table shows how the marks should be awarded for indicative points would score zero marks for reasoning.

structure and lines of reasoning.

Number of marks awarded If there is any incorrect chemistry, deduct mark(s) from the reasoning. If no reasoning

for structure and sustained mark(s) awarded do not deduct mark(s).

lines of reasoning

Answer shows a coherent and logical

structure with linkages and fully 2

sustained lines of reasoning

demonstrated throughout.

Answer is partially structured with

some linkages and lines of reasoning. 1

Answer has no linkages between

points and is unstructured. 0

Indicative content: Do not award reference to reflux of butanoic acid

IP1 mention of refluxing (and excess oxidising agent) Accept diagram of workable reflux arrangement even if not fully labelled.

Allow direct/indirect heating

IP2 diagram of reflux equipment with vertical condenser

and correct water flow

Ignore method of adding the alcohol, e.g. butan-1-ol may be added down

reflux condenser

Allow direct heating with Bunsen burner or electrical heater/

Isomantle/thermomantle etc.

IP3 anti-bumping granules and suitable method of heating Allow just an arrow labelled heat as shown in the diagram above

IP4 mention of distillation at suitable temperature Any range or value between 120 oC and the maximum temperature of 170

oC for distillation of butanoic acid

Do not award distillation of the butan-1-ol

IP5 diagram of distillation apparatus with sloping

condenser and collecting vessel

Penalise incorrect water flow/unlabelled water flow in condenser once

only in IP2 or IP5

Penalise gaps in joints between the equipment once only in IP2 or IP5

IP6 inclusion of thermometer (pocket) on left-hand side (in

this diagram) and opening for gaseous escape on right-

hand side (in this diagram)

If initial oxidation under reflux is not mentioned then only IP4 and IP6 are

obtainable

(Total for Question 7 = 13 marks)

Question

Acceptable Answer Additional Guidance Mark

Number

How to answer it

Reactions, Energetics and Functional Group Chemistry of Butan-1-ol

📚 What this question tests

This question assesses core AS Level organic chemistry and energetics: identifying intermolecular forces in alcohols, constructing enthalpy level diagrams for combustion, functional group testing using chemical reagents, controlling oxidation pathways (distillation vs. reflux), and writing detailed experimental procedures for organic preparations.

Part (a): Intermolecular Forces

Identifying bonding in liquid butan-1-ol

✅ Correct Answer

C (hydrogen bonding, permanent dipole-dipole forces and London forces)

💡 Key Knowledge

London forces exist between all molecules due to fluctuating temporary dipoles.
Permanent dipole-dipole forces arise from the polar C-O bonds.
Hydrogen bonding occurs because of the highly electronegative oxygen bonded directly to hydrogen (-OH group).

❌ Common Errors

Students often select option A, forgetting that London forces are universal and present in all molecular substances alongside stronger specific interactions.

Mark: 1 mark

Part (b): Enthalpy Level Diagrams

Representing complete combustion thermochemistry

✅ Correct Answer & Layout

Reactants level: CH₃CH₂CH₂CH₂OH(l) + 6O₂(g) positioned higher up on the vertical enthalpy axis.
Products level: 4CO₂(g) + 5H₂O(l) positioned lower down, reflecting an exothermic reaction (negative enthalpy change).
Arrow: A straight, vertical line pointing downwards from the reactant level to the product level, clearly labelled ΔH = -2675.6 kJ mol⁻¹ (or ΔcH ).

🧠 Exam Technique

Never draw a double-headed arrow for an enthalpy change. Ensure your arrow goes strictly from level to level without gaps or double heads. Ignore activation energy "humps" unless specifically asked for a reaction profile with an intermediate peak.

Mark: 2 marks

Part (c)(i): Functional Group Testing

Identifying alcohol functional groups

✅ Correct Answer

B (phosphorus(V) chloride PCl₅(s) gives steamy fumes)

❌ Common Errors

Choosing option A (white smoke - which is incorrect; HCl forms steamy/misty fumes, not solid white smoke). Option C and D incorrectly treat alcohols as if they react with weak carbonates like carboxylic acids do.

Mark: 1 mark

Part (c)(ii) & (iii): Aldehyde Production and Testing

Selective oxidation and chemical confirmation

🧠 Exam Technique: Part (ii) - Butanal Production

To stop oxidation at the aldehyde stage and prevent carboxylic acid formation, you must set equipment for distillation so that the volatile aldehyde boils off and is removed immediately as it forms.

✅ Correct Answer: Part (iii) - Aldehyde Test

Reagent: Add Tollens' reagent, Fehling's solution, or Benedict's solution and warm.
Result: Tollens' gives a silver mirror; Fehling's/Benedict's gives a red/brown precipitate.

Marks: (ii) = 1 mark, (iii) = 2 marks

Part (c)(iv): Multi-Step Organic Preparation

Preparing butanoic acid from butan-1-ol (Extended 6-mark response)

💡 Key Chemistry Steps (Indicative Content)

IP1 & IP3: Use reflux with an excess of acidified potassium dichromate( VI ) and add anti-bumping granules to ensure smooth boiling.
IP2: Set up a reflux condenser vertically with continuous cold water flowing in at the bottom and out at the top (open system at the top, no sealing).
IP4 & IP5: Following complete oxidation/reflux, rearrange the glassware for distillation. Collect the fraction boiling within the appropriate temperature range (e.g., between 120 °C and 170 °C, noting butanoic acid boils at 166 °C).
IP6: Include a thermometer with its bulb positioned at the T-junction of the distillation head to accurately measure the boiling point of the vapour being collected.

🧠 Structuring Your 6-Mark Answer

This extended response is marked using levels of reasoning combined with indicative points (IPs). Make sure you explicitly mention: (1) reflux with excess oxidising agent, (2) vertical condenser setup, (3) anti-bumping granules, (4) changing apparatus to distillation, (5) correct temperature collection range around 166 °C, and (6) correct thermometer placement.

Marks: Up to 6 marks (4 for indicative content + 2 for quality of structured reasoning)

Topics

Physical Chemistry · Organic Chemistry · Core Practicals · Topic 2: Bonding and Structure · Topic 8: Energetics I · Topic 6: Organic Chemistry I · Core Practical 5: Investigate the oxidation of ethanol · Core Practical 7: Identify unknown organic liquids and inorganic solids · Topic 18: Organic Chemistry III

Question and mark scheme from the Edexcel A-Level Chemistry examination, AS Paper 2, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.