Ethene is an alkene.
(a) Describe a test to distinguish between ethane and ethene. Give the result for each. [2]
(b) Name the product formed when ethene reacts with bromine. [1]
(c) Give the structural formula of an isomer of but-1-ene, CH₂=CHCH₂CH₃, that is also an alkene. [1]
- (a) add bromine water (allow bromine solution)(1)
- (a) ethene: orange to colourless (allow brown / yellow for orange; reject 'clear'); ethane: stays orange / no change(1)
- (b) 1,2-dibromoethane (allow dibromoethane; allow CH₂BrCH₂Br)(1)
- (c) CH₃CH=CHCH₃ (but-2-ene) or CH₂=C(CH₃)₂ (methylpropene) (allow displayed formulae; reject CH₃CH₂CH=CH₂, which is but-1-ene again)(1)
- Answer: (a) bromine water: decolourised by ethene, stays orange with ethane (b) 1,2-dibromoethane (c) CH₃CH=CHCH₃
- Examiner tip: 'Clear' is not the same as 'colourless' — orange bromine water turns COLOURLESS.