Physical properties
3 marks · NormalHexene (C6H12) and butene (C4H8) are both alkenes. Explain why hexene has a higher boiling point than butene, referring to their structure and trends among alkenes (C2–C4).
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Must show: Hexene molecules are larger than butene molecules, Boiling point increases as the number of carbon atoms increases in alkenes, Explanation: more atoms leads to stronger intermolecular forces
Common mistakes: Confusing boiling points with reactivity; Incorrect statement about number of hydrogen atoms
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Marking points
B1 · 1 mark · Correctly identifies hexene has more carbon atoms (longer chain)
B2 · 1 mark · Correctly states that boiling points rise with increasing number of carbons (or chain length) among alkenes (C2–C4 upward)
B3 · 1 mark · Explains the trend: larger molecules/greater surface area/stronger intermolecular forces
Worked solution
Hexene has more carbon atoms than butene, so its molecules are larger.
As the number of carbons in the alkene increases from C2 upward, the boiling point increases.
Larger molecules have stronger intermolecular forces, so more energy is needed to boil hexene than butene.