Methoxymethane, \({\text{C}}{{\text{H}}_{\text{3}}}{\text{OC}}{{\text{H}}_{\text{3}}}\), and ethanol, \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}\), have the same relative molecular mass. Explain why methoxymethane has a much lower boiling point than ethanol.

methoxymethane is very weakly polar

weak van der Waals’/dipole-dipole forces exist between methoxymethane molecules;

Accept alternatives to van der Waals’ such as London and dispersion forces.

ethanol contains a hydrogen atom bonded directly to an electronegative oxygen atom / hydrogen bonding can occur between two ethanol molecules / intermolecular hydrogen bonding in ethanol;

the forces of attraction between molecules are stronger in ethanol than in methoxymethane / hydrogen bonding stronger than van der Waals’/dipole-dipole attractions;

Award [2 max] if covalent bonds breaking during boiling is mentioned in the answer.

Penalize only once if no reference given to intermolecular nature of hydrogen bonding or van der Waal is missing.

This question was not answered well and many candidates showed they were confused about the different intermolecular forces present between the molecules. Also, many seemed to be trying to explain the difference in boiling point based on the differing strengths of covalent bonds that were present. Those that did correctly identify the stronger hydrogen bonding in ethanol leading to its higher boiling point often forgot to mention that it was intermolecular and between the molecules of ethanol.