Edexcel IAL Chemistry Topic 7 Intermolecular forces

Identify every force present, compare electron number, shape and hydrogen-bond donors or acceptors and connect total attraction to boiling, solubility or layer position.

Exam points

Classify London forces, permanent dipoles and hydrogen bonding from structures.
Explain boiling trends through electron number, molecular shape and hydrogen bonding.
Interpret solvent, hydration and layer evidence for molecular and ionic substances.

Covered syllabus points

7.1—The nature of the following intermolecular forces: i London forces (instantaneous dipole-induced dipole) ii permanent 7.2—The interactions in molecules, such as H2O, liquid NH3 and liquid HF, which give rise to hydrogen bonding 7.3—The following anomalous properties of water resulting from hydrogen bonding: i its high melting and boiling temperature when 7.4—Predict the presence of hydrogen bonding in molecules analogous to those mentioned in 7.2 7.5—Understand, in terms of intermolecular forces, physical properties shown by substances 7.6—Factors that influence the choice of solvents

[Maximum number: 3]

Some diesel cars contain an extra catalytic converter for the reduction of nitrogen oxides $\left(\mathrm{NO}_{\mathrm{x}}\right)$ in exhaust gases.
A solution of urea is used for this process.

Figure for Question Topic 7: Intermolecular Forces question 1 — Edexcel A-Level Chemistry AS

urea

Urea has a melting temperature of $133^{\circ} \mathrm{C}$ .

Explain why this value is higher than expected for a relatively small molecule.

[Maximum number: 2]

This question is about hydrogen bonding.

(a)

Which property is not due to hydrogen bonding?
- A ice has a lower density than water at $0^{\circ} \mathrm{C}$
- B hydrogen fluoride has a higher boiling temperature than hydrogen chloride
- C H-H bond enthalpy is greater than Si-H bond enthalpy
- D alcohols are less volatile than alkanes with a similar molar mass

[ 1 ]

(b)

Which diagram best represents a hydrogen bond between two water molecules?
□ A

Figure for Question (b) — Edexcel A-Level Chemistry AS

□ B

□ C

□ D

[ 1 ]

Figure for Answer to Question (b) — Edexcel A-Level Chemistry AS

The only correct answer is A

B is not correct because the 2 water molecules do not form a hydrogen bond between two hydrogen atoms

C is not correct because the hydrogen bond angle is not $104.5^{\circ}$

D is not correct because the angle between 2 water molecules should be $180^{\circ}$ and water molecules should not have a bond angle of $180^{\circ}$

(1)

[Maximum number: 1]

Which is not correct about ice?

ice has a lower density than water

$\mathrm{H}_{2} \mathrm{O}$ molecules are further apart in ice than in water

the H-O-H bond angle is the same in ice and in water

$\mathrm{H}_{2} \mathrm{O}$ molecules in ice are held together by hydrogen bonds

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Covered syllabus points

Topic 7: Intermolecular Forces question 1

Topic 7: Intermolecular Forces question 2

Question (a)

Question (b)

Topic 7: Intermolecular Forces question 3