Edexcel A-Level Chemistry Paper 2, November 2020: Question 1
7 marks · Medium difficulty · Short Open Response
Answer questions about the bonding, bond length, and hydrogen bonding intermolecular interactions of methanol, CH3OH.
Practise this questionQuestion
Question text
1 This question is about methanol, CH3OH.
(a) Draw a dot-and-cross diagram to show the bonding in a molecule of methanol.
Show outer shell electrons only.
(2)
(b) Predict which bond has the shortest bond length in a molecule of methanol.
(1)
(c) Methanol is soluble in water.
(i) State the strongest type of intermolecular force that occurs between
molecules of methanol and water.
(1)
(ii) Draw a labelled diagram to show the interaction named in (c)(i) between one
molecule of methanol and one molecule of water.
Include any relevant lone pairs and dipoles in your diagram.
(3)
*P62669A0232*
(Total for Question 1 = 7 marks)
Mark scheme
Show the mark scheme
How to answer it
Structure, Bonding & Intermolecular Forces: Methanol
What this question tests
This question assesses core foundational chemistry concepts including covalent bonding representations (dot-and-cross diagrams), bond length relationships, identifying intermolecular forces, and applying precise spatial and electrostatic awareness to hydrogen bonding diagrams between polar molecules.
Drawing the Outer Shell Electrons of Methanol (CH₃OH)
✅ Correct Answer
All bonding pairs shown correctly (C-H, C-O, O-H) using dots and crosses, alongside two lone pairs clearly positioned on the oxygen atom.
💡 Key Knowledge
Carbon contributes 4 outer electrons, hydrogen 1, and oxygen 6 (total 14 valence electrons / 7 pairs). Oxygen needs 2 bonding pairs (to C and H) and retains 2 non-bonding lone pairs to satisfy an octet.
🧠 Exam Technique
You can use any combination of symbols (dots/crosses or all dots). Non-bonding electrons on oxygen can be grouped as two separate pairs, four together, or 3 and 1. Inner shell electrons are completely ignored.
❌ Common Errors
Forgetting to draw the lone pairs on the oxygen atom, or drawing incorrect numbers of electrons around carbon (failing to give carbon an octet of 8 shared electrons).
Identifying the Shortest Bond in Methanol
✅ Correct Answer
O-H (Accept OH ; do not award -O-H with loose dashes).
💡 Key Knowledge
Hydrogen has a much smaller atomic radius (1s shell only) compared to carbon and oxygen. Consequently, bonds involving hydrogen atoms (like O-H and C-H) are generally shorter and stronger than bonds between heavier period 2 elements (like C-O). Furthermore, the O-H single bond is shorter than C-H bonds due to oxygen's higher nuclear charge pulling its bonding pair closer.
🧠 Exam Technique
Keep your answer concise. Simply naming the bond directly answers the command word "Predict".
Naming the Strongest Intermolecular Force
✅ Correct Answer
Hydrogen bonding
💡 Key Knowledge
Hydrogen bonding occurs when hydrogen is covalently bonded to a highly electronegative atom with lone pairs (Fluorine, Oxygen, or Nitrogen - F, O, N). Both methanol and water contain O-H bonds, allowing intermolecular hydrogen bonding between them.
❌ Common Errors
Vague answers like "dipole-dipole forces" or "permanent dipole-permanent dipole". While hydrogen bonding is a subset of dipole-dipole interactions, examiners strictly require the specific term hydrogen bonding for the mark.
Visualising Methanol-Water Interactions
✅ Correct Answer
A clearly sketched diagram showing one methanol molecule interacting with one water molecule via a dashed line representing a hydrogen bond, complete with lone pairs, partial charges ( δ+ / δ- ), and a linear 180° bond angle across the hydrogen bond.
💡 Key Knowledge
A hydrogen bond requires a linear alignment involving the hydrogen donor, the hydrogen atom itself, and the lone pair on the electronegative acceptor atom ( O-H···O ). This mandates a 180° angle centered around the bridging hydrogen atom.
🧠 Exam Technique
To secure all 3 marks, check off your diagram against these three criteria:
1. At least one lone pair shown on an oxygen atom involved in the hydrogen bond.
2. A dashed line representing the hydrogen bond connecting H to O, with the O-H···O angle drawn straight at approximately 180° .
3. Correct partial charges ( δ+ on the H involved in the hydrogen bond, and δ- on the oxygen atoms).
❌ Common Errors
Drawing the hydrogen bond with a bent, sharp angle rather than a linear 180° layout, or omitting partial charges ( δ+ / δ- ) entirely.
Topics
Physical Chemistry · Organic Chemistry · Topic 2: Bonding and Structure · Topic 6: Organic Chemistry I
Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 2, November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.