Quick answer: Intermolecular forces are the attractions between molecules: London forces act between all particles and grow with the number of electrons, permanent dipole–dipole forces act between polar molecules, and hydrogen bonds act when H bonded to N, O or F meets a lone pair. This Chemistry 11-12 test on intermolecular forces has 8 questions worth 20 marks, to do in 45 minutes: boiling bromine, krypton and argon and alkanes and alcohols. The mark scheme is on a separate page; free printable PDF.
This test covers the three types of intermolecular force, boiling points and the energy of changes of state. Answer every question, name the forces precisely and show your working. The total is 20 marks.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB S2.2
Question 1 Boiling bromine (2 marks)
Bromine, Br₂, is a non-polar liquid. State the type of force broken when it boils and explain why the Br–Br bonds are not broken. (2 marks)Question 2 Krypton and argon (3 marks)
Krypton boils at 120 K and argon at 87 K. Explain the difference. (3 marks)Question 3 Alkanes and alcohols (4 marks)
The graph shows boiling points of alkanes and alcohols with the same number of carbons.- Describe the difference between the two series. (1 mark)
- Explain why the alcohols boil higher. (2 marks)
- Explain why the gap narrows as the chain gets longer. (1 mark)
Question 4 Propanol and methoxyethane (2 marks)
Propan-1-ol (CH₃CH₂CH₂OH) boils at 97 °C and methoxyethane (CH₃OCH₂CH₃) at 7 °C. Explain the difference. (2 marks)Question 5 Hydrogen bond in water (2 marks)
Describe how a hydrogen bond forms between two water molecules. (2 marks)Question 6 Energy to vaporise water (2 marks)
The enthalpy of vaporisation of water is 40.7 kJ mol⁻¹. Calculate the energy to vaporise 36.0 g of water (M = 18.0 g mol⁻¹). (2 marks)Question 7 Why ice floats (3 marks)
Explain why ice is less dense than liquid water. (3 marks)Question 8 Pentane and butan-1-ol (2 marks)
Pentane boils at 36 °C and butan-1-ol at 117 °C. They have similar numbers of electrons. Explain why butan-1-ol boils higher. (2 marks)
