Organic chemistry — Question 6

6a)

Hexane has a higher boiling point than pentane because a longer carbon chain has a larger molar mass, which increases dispersion forces.

• predicts that hexane has a higher boiling point [1 mark]

• explains that increasing chain length increases dispersion forces [1 mark]

6b)

Butanal is polar, and pentane is non-polar. Butanal forms dipole–dipole interactions that are stronger than the dispersion forces in pentane; therefore, butanal has a higher boiling point.

• identifies that butanal is polar and/or has dipole-dipole forces [1 mark]

• identifies that pentane is non-polar and/or only has dispersion forces [1 mark]

• explains that butanal has a higher melting point due to stronger intermolecular forces [1 mark]

6c)

Propanoic acid and butanol are highly soluble in water because the polar COOH and OH groups can form hydrogen bonds with water.

• identifies that propanoic acid and butanol are highly soluble in water [1 mark]

• explains that solubility is due to hydrogen bonding with water [1 mark]

6d)

Primary alcohol. The OH group is attached to a carbon that is attached to one carbon atom.

• identifies primary alcohol [1 mark]

• explains that the OH group is attached to a carbon that is attached to one carbon atom [1 mark]

6e)

ethyl methanoate

• names ester as ethyl methanoate [1 mark]