Alkenes ppt slides
- 1. Alkenes (II)
- 2. Overview
- 4. Why do alkenes undergo addition reactions?Addition ReactionsCarbon-carbon double bonds in alkenes are reactive. readily undergoes addition reactions
- 5. Addition Reactions +Unsaturated hydrocarbonSaturated organic compoundIn an addition reaction, carbon-carbon double bonds become single bonds. This means that an unsaturated hydrocarbon becomes a saturated organic compound.
- 6. Types of Addition ReactionsHHHHHH+++Br2H2HCCCCCCGeneral Equation:HHHHHHHHHHHHOHHCCHHCCHHCCHBrBrHHHOH
- 7. Used to test for the presence of an alkene or unsaturation.More on Bromination…If an alkene or unsaturation is present, bromine solution will be rapidly decolourised
- 8. The “bromine number” is used to test for degree of unsaturation in gasoline samples!More on Hydrogenation…
- 9. More on hydrogenation…Used in the production of margarine200 °C, nickel catalystHydrogen + vegetable oil MargarineThe greater the amount of hydrogen used, the more ___________ the fat and the more _________ the margarine becomes. saturatedsolid
- 10. Alkenes can also undergo combustion reactionsCombustion ReactionsFrom your knowledge on combustion of alkanes, write the equation for the combustion of ethene:C2H4 + 3O2 2CO2 + 2H2OAny difference between the combustion of alkanes and alkenes?smokierAns: Alkenes burn with a ___________ flame than alkanes with asimilar number of carbon atoms. (Due to the relatively higherpercentages of carbon in alkenes)
- 11. Fats and OilsSaturated fatsNo double bond in the fat moleculesMonounsaturated fatsOne double bond per fat moleculePolyunsaturated fatsMore than one double bond per fat moleculeA label from sunflower oil
- 12. Nutritional FactsAvoid foods high in saturated fat!
- 13. Nutritional dataAvoid oils high in saturated fat. Opt for healthier options like sunflower oil!
- 14. Manufacture of AlkenesShort-chain alkenes are useful as starting materials for making ethanol and plastics. How can we manufacture alkenes?crackingBy __________________ of petroleumCracking is the _______________ of long-chain hydrocarbons into ___________________.On the industrial scale, cracking is done by passing the petroleum fraction over a _____________ (aluminium oxide or silicon(IV) oxide) at a _________________ of 600°C.breaking downsmaller moleculescatalysttemperatureCracking
- 15. Products of Cracking3 possible types of productsTry this:Write an equation for the cracking of heptane (C7H16). (Note: There are a few possible answers)One possible answer: C7H16 C3H6 + C4H8 + H2
- 16. Video time: Cracking in the school laboratory3. Describe some characteristics of the gases collected.They have a smell, are flammable andunsaturated (contain C=C bonds).4. Which other test can be used to test for unsaturation?Click hereAdd acidified potassium permanganateto the unknown. If it turns brown orcolourless, the unknown is unsaturated.1. What is the compound that is cracked?Paraffin2. What is the catalyst used?5. Why is the displacement of watermethod used to collect the products?Pumice stones / broken flowerpotsThe organic products are insoluble inwater.
- 17. Why the need for cracking?<Shortfall of petrol>Excess of fuel oilCracking of heavier fractions like fuel oil can be used to make up for the shortfall of lighter fractions like petrol.
- 18. In short, cracking is used to produce:Hydrogen (fuel and raw materialfor Haber process)Petrol (fuel)Short-chain alkenes(starting materials formaking ethanol andplastics)
- 19. Steam cracking adoptedProduce large amounts of ethene, propene and butene for making plasticsCracking plants in Jurong island and PulauBukomIn the Singapore contextSteam cracking plant in SingaporeJurong islandPulauBukom
- 20. 10 minutes to construct concept maps!Summary123Cracking