Intermolecular forcesEdexcel A-Level Chemistry: Subtopic test

1. 1
   Butane, pentane and hexane boil at about 0 °C, 36 °C and 69 °C respectively. An isomer of pentane, 2,2-dimethylpropane, boils at about 10 °C.

   (a)

   Which type of intermolecular force is the main attraction between alkane molecules?

   [1 mark]

   • AHydrogen bonds
   • BLondon forces
   • CPermanent dipole–dipole forces
   • DIonic bonds

   (b)

   Which statement best explains why 2,2-dimethylpropane has a lower boiling temperature than pentane?

   [1 mark]

   • AIts covalent bonds are weaker
   • BIt has fewer electrons per molecule
   • CIts molecules are more compact, so there is less surface contact and weaker London forces
   • DIt has a permanent dipole that weakens the attraction between molecules

   (c)

   Explain why the boiling temperature increases from butane to hexane.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The boiling temperatures of the hydrogen halides are: HF 20 °C, HCl −85 °C, HBr −67 °C and HI −35 °C.

   (a)

   Which intermolecular force explains why hydrogen fluoride has the highest boiling temperature of the four?

   [1 mark]

   • ALondon forces only
   • BPermanent dipole–dipole forces only
   • CIonic bonding
   • DHydrogen bonding

   (b)

   Which of these molecules can form hydrogen bonds with other molecules of the same compound?

   [1 mark]

   • ACH₃CH₂OH
   • BCH₃OCH₃
   • CCH₃Br
   • DCH₄

   (c)

   Explain why the boiling temperature rises from HCl to HI, even though the bonds become less polar.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Ice floats on liquid water. Water boils at 100 °C, whereas hydrogen sulfide, H₂S, which has a similar shape and more electrons, boils at about −60 °C.

   (a)

   Explain why ice is less dense than liquid water.

   [3 marks]

   (b)

   Explain why water has a much higher boiling temperature than hydrogen sulfide.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Ethanol, C₂H₅OH, boils at 78 °C, whereas propane, C₃H₈, which has the same number of electrons, boils at −42 °C. Ethanol mixes completely with water but bromoethane, C₂H₅Br, does not. Sodium chloride dissolves in water but not in hexane.

   (a)

   Explain why ethanol has a much higher boiling temperature than propane.

   [6 marks]

   (b)

   Explain the solubility behaviour described: sodium chloride dissolving in water but not in hexane, ethanol mixing with water, and bromoethane not mixing with water.

   [6 marks]

   Total for question 4: 12 marks

End of questions