OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2024: Question 2

1 mark · Easy difficulty · Multiple Choice

Identify the type of bonding or intermolecular forces responsible for water's anomalous properties such as high melting/boiling points and ice being less dense than water.

Practise this question

Question

Multiple choice question asking which statement explains water's anomalous properties of relatively high melting and boiling points and ice being less dense than water. Options are A: covalent bonding within water molecules, B: hydrogen bonding between water molecules, C: induced dipole-dipole interactions (London forces) between water molecules, and D: ionic bonding between water molecules.
Question text

2 Water has the anomalous properties below.

• Water has relatively high melting and boiling points.

• Ice is less dense than water.

Which statement explains these anomalous properties?

A The covalent bonding within water molecules.

B The hydrogen bonding between water molecules.

C The induced dipole–dipole interactions (London forces) between water molecules.

D The ionic bonding between water molecules.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 2 is B, worth 1 mark.

2 B 1

How to answer it

Anomalous Properties of Water

What this question tests

This question assesses your understanding of intermolecular forces, specifically hydrogen bonding, and how these forces account for the unique physical properties of water (such as its unexpectedly high melting/boiling points and the lower density of ice compared to liquid water).

Question 2

Anomalous Properties of Water

✅ Correct Answer

B — The hydrogen bonding between water molecules.

Mark Awarded: 1 / 1

💡 Key Knowledge

  • Hydrogen bonds are the strongest type of intermolecular force, occurring when hydrogen is covalently bonded to highly electronegative atoms (F, O, N).
  • In ice, water molecules are held in a rigid, open lattice structure by hydrogen bonds, keeping molecules further apart and making ice less dense than water.
  • Additional thermal energy is required to break these extensive hydrogen bonds, resulting in unusually high melting and boiling points.

🧠 Exam Technique

Read the question carefully to distinguish between intramolecular bonding (covalent bonds holding the atoms within the H₂O molecule) and intermolecular forces (forces acting between separate molecules). Covalent bonds dictate molecular identity, but intermolecular forces dictate physical properties like melting/boiling points and density.

❌ Common Errors

  • Choosing A (covalent bonding): Students often confuse intramolecular covalent bond strength with the intermolecular forces that must be overcome during melting or boiling.
  • Choosing C or D: Assuming London forces are dominant in polar molecules, or incorrectly assigning ionic properties to simple covalent molecules like water.

Topics

Module 2: Foundations in chemistry · 2.2 Electrons, bonding and structure

Question and mark scheme from the OCR A-Level Chemistry examination, Periodic table, elements and physical chemistry (01), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.