RI 2024 Alkenes Tutorial Self-Check Answers

-1- Raffles Institution Year 5 H2 Chemistry 2024 Tutorial 11 – Alkenes (Suggested Answers) Answers to Self-Check Questions Q1 (a) trans-3-methylhex-3-ene (b) trans-7-methyloct-3-ene (c) 2,4-dimethylpent-1-ene (d) trans-2,3,4,5-tetramethylhexa-1,3,5-triene (e) (f) Q2 Reagents & conditions Type of reaction Observations Structural formulae of organic products (a) H2(g), Ni catalyst, heat reduction No observable change (b) Br2 in CCl4 electrophilic addition Orange-red Br2 is decolourised. (c) Br2(aq) electrophilic addition Orange Br2(aq) is decolourised. (major product) (d) HBr(g) electrophilic addition No observable change (major product) (e) KMnO4(aq), NaOH, cold mild oxidation Purple KMnO4 is decolourised AND Brown-black precipitate of MnO2 is formed. (f) KMnO4(aq), H2SO4(aq), heat strong oxidation Purple KMnO4 is decolourised AND colourless gas evolved (CO2) gives white ppt with limewater / Ca(OH)2(aq).

-2- (g) cold conc. H2SO4, followed by heating with H2O electrophilic addition No observable change (major product) Q3 (a) OH OH propan-1-ol propan-2-ol (b) OH + H2O or OH + H2O (c)(i) aluminium oxide or alumina (c)(ii) Carbon is the substance responsible for the black colour. It is produced from the thermal decomposition of the alcohol. Note: the thermal decomposition of the ethanol is a side reaction. (c)(iii) This is done so that the cold water would not be sucked back into the hot test -tube, thereby causing it to crack. (d)(i) KOH in ethanol, heat (d)(ii) Type of reaction: elimination Equation: Cl + OH- + Cl - + H2O 4 5 6 7 8 9 10 11 12 C B D C C A A C C