Edexcel A-Level Chemistry Paper 2, November 2021: Question 5
6 marks · Medium difficulty · Short Open Response
Identify functional groups, explain the effect of water on synthetic oil, name the crude oil separation process, and compare boiling points of compound X and hydrocarbons.
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Question text
5 Compound X is a component of synthetic oils used as lubricants, for instance in the
gearboxes of ships.
OH OH O
O
compound X
(a) Name the three functional groups present in compound X.
(2)
(b) The effectiveness of this synthetic oil is much reduced if it is
contaminated with water.
Give, in terms of a chemical reaction, a possible reason for this.
(1)
(c) An alternative to synthetic oil is known as mineral oil and consists solely of
hydrocarbons separated from crude oil.
(i) What is the name of the process used to separate different hydrocarbons from
crude oil?
(1)
A cracking
B reforming
C fractional distillation
D heating under reflux
(ii) Explain why compound X is likely to have a higher boiling temperature than
hydrocarbons of a similar molecular mass and shape.
A detailed description of how the intermolecular forces arise is not required.
(2)
… *P65464A0628*
(Total for Question 5 = 6 marks)
Mark scheme
Show the mark scheme
Question
Answer Additional Guidance Mark
Number
5(a) (2)
• Name of the three functional groups (2) Alcohol / diol, ester and alkene
Allow hydroxy / hydroxyl (group) for alcohol
Ignore primary
Do not award incorrect structures of functional groups in
conjunction with correct name
Do not award secondary or tertiary alcohol
Three correct functional groups scores (2)
Two correct functional groups scores (1)
One or zero correct functional groups (0)
Four groups named with three correct scores (1)
Question
Answer Additional Guidance Mark
Number
5(b) An answer that makes reference to the following point Ignore reference to H-bonds between water and OH (1)
groups
• the ester (functional group) will react (with the
water) in a hydrolysis reaction Allow ‘hydrolysis reaction’ if equation showing break up
of ester group also shown
Question
Answer Mark
Number
5(c)(i) The only correct answer is C (fractional distillation) (1)
A is incorrect because the process is used to produce smaller hydrocarbons
B is incorrect because the process is used to produce branched and cyclic hydrocarbons
D is incorrect because the process is used to heat reaction mixtures
Question
Answer Additional Guidance Mark
Number
5(c)(ii) An explanation that makes reference to one of the following pairs of (2)
points
Either Ignore references to dipole-dipole
• the OH groups (in compound X) can form hydrogen bonds interactions
(1) Allow ‘the oxygen (in compound X) can
form hydrogen bonds’)
• so more energy is needed to vaporise compound X / break Allow ‘more energy is needed to break
intermolecular forces in compound X (1) bonds in compound X’ if H bonds
discussed
Any reference to the breaking of
Or covalent bonds loses M2 only
• hydrocarbons have only London forces, but compound X has
hydrogen bonds (as well) (1)
• hydrogen bonds are stronger (than London forces) (1)
(Total Question 5 = 6 marks)
How to answer it
Compound X and Synthetic Oils Study Guide
What this question tests
- Identifying organic functional groups from skeletal and structural formulae.
- Understanding chemical stability and reactions of functional groups in the presence of water (hydrolysis of esters).
- Knowledge of industrial separation techniques for crude oil.
- Relating intermolecular forces (specifically hydrogen bonding vs London forces) to physical properties such as boiling temperature.
Name the three functional groups present in compound X
✅ Correct Answer
You must name all three:
- Alcohol (accept hydroxy or hydroxyl )
- Ester
- Alkene
💡 Key Knowledge
- Alcohol: Look for the -OH groups attached to saturated carbon chains.
- Ester: Look for the ester linkage -COO- (or -C(=O)-O- ).
- Alkene: Look for the carbon-carbon double bond C=C embedded in the long chain.
❌ Common Errors
- Adding extra descriptors like "primary alcohol"—the mark scheme ignores "primary", but adding incorrect classifications like "secondary" or "tertiary" loses credit.
- Listing incorrect chemical structures alongside the correct name.
- Failing to name all three groups (2 correct = 1 mark; 3 correct = 2 marks).
Why is the effectiveness of the synthetic oil reduced if contaminated with water?
✅ Correct Answer
The ester functional group will react with water in a hydrolysis reaction (breaking down the lubricating oil molecule).
🧠 Exam Technique
- Keep your chemical reasoning direct and precise. You must link water to the destruction or reaction of the oil component.
- Mentioning "hydrolysis" or stating that the ester link breaks down secures the mark instantly.
❌ Common Errors
- Just saying "they mix poorly" or discussing simple physical phase separation. The question explicitly asks for a reason in terms of a chemical reaction.
- Writing about hydrogen bonding between water and the -OH groups (this is irrelevant to the reduction in lubricating effectiveness through chemical degradation).
Name the process used to separate different hydrocarbons from crude oil
✅ Correct Answer
C — fractional distillation
💡 Why the other options are wrong:
- A (cracking): Used to break long-chain alkanes into smaller, more useful alkenes and alkanes.
- B (reforming): Converts straight-chain alkanes into branched-chain and cyclic hydrocarbons.
- D (heating under reflux): A laboratory technique used to heat reaction mixtures without losing volatile vapors.
Explain why compound X is likely to have a higher boiling temperature than hydrocarbons of a similar molecular mass and shape
✅ Correct Answer
Any valid combination of two core points:
- Compound X has -OH groups that can form hydrogen bonds.
- Therefore, more energy is needed to vaporise compound X / break its intermolecular forces compared to hydrocarbons.
- Alternatively: Hydrocarbons only have London forces, whereas compound X also has hydrogen bonds, which are stronger than London forces.
🧠 Exam Technique & Examiner Guidance
- State both what type of intermolecular force is present in compound X (hydrogen bonding) and how it affects energy requirements.
- Make sure you compare it explicitly to the hydrocarbon's intermolecular forces (London forces).
❌ Common Errors
- CRITICAL TRAP: Mentioning the breaking of covalent bonds instead of intermolecular forces will instantly lose the second marking point (M2). Boiling points involve overcoming intermolecular forces, not covalent bonds!
- Referring to dipole-dipole interactions instead of hydrogen bonds where applicable.
Topics
Organic Chemistry · Physical Chemistry · Topic 6: Organic Chemistry I · Topic 17: Organic Chemistry II · Topic 2: Bonding and Structure
Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.