Alkenes ppt slides


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Alkenes ppt slides

  1. 1. Alkenes (II)<br />
  2. 2. Overview<br />
  3. 3.
  4. 4. Why do alkenes undergo addition reactions?<br />Addition Reactions<br />Carbon-carbon double bonds in alkenes are reactive. <br />readily undergoes addition reactions<br />
  5. 5. Addition Reactions <br />+<br />Unsaturated hydrocarbon<br />Saturated organic compound<br />In an addition reaction, carbon-carbon double bonds become single bonds. This means that an unsaturated hydrocarbon becomes a saturated organic compound. <br />
  6. 6. Types of Addition Reactions<br />H<br />H<br />H<br />H<br />H<br />H<br />+<br />+<br />+<br />Br2<br />H2<br />H<br />C<br />C<br />C<br />C<br />C<br />C<br />General Equation:<br />H<br />H<br />H<br />H<br />H<br />H<br />H<br />H<br />H<br />H<br />H<br />H<br />OH<br />H<br />C<br />C<br />H<br />H<br />C<br />C<br />H<br />H<br />C<br />C<br />H<br />Br<br />Br<br />H<br />H<br />H<br />OH<br />
  7. 7. Used to test for the presence of an alkene or unsaturation.<br />More on Bromination…<br /><ul><li>If an alkene or unsaturation is present, bromine solution will be rapidly decolourised
  8. 8. The “bromine number” is used to test for degree of unsaturation in gasoline samples!</li></li></ul><li>More on Hydrogenation…<br />
  9. 9. More on hydrogenation…<br />Used in the production of margarine<br />200 °C, nickel catalyst<br />Hydrogen + vegetable oil Margarine<br /><ul><li>The greater the amount of hydrogen used, the more ___________ the fat and the more _________ the margarine becomes. </li></ul>saturated<br />solid<br />
  10. 10. Alkenes can also undergo combustion reactions<br />Combustion Reactions<br /><ul><li>From your knowledge on combustion of alkanes, write the equation for the combustion of ethene:</li></ul>C2H4 + 3O2 2CO2 + 2H2O<br /><ul><li>Any difference between the combustion of alkanes and alkenes?</li></ul>smokier<br />Ans: Alkenes burn with a ___________ flame than alkanes with a<br />similar number of carbon atoms. (Due to the relatively higher<br />percentages of carbon in alkenes)<br />
  11. 11. Fats and Oils<br /><ul><li>Saturated fats</li></ul>No double bond in the fat molecules<br /><ul><li>Monounsaturated fats</li></ul>One double bond per fat molecule<br /><ul><li>Polyunsaturated fats</li></ul>More than one double bond per fat molecule<br />A label from sunflower oil<br />
  12. 12. Nutritional Facts<br />Avoid foods high in saturated fat!<br />
  13. 13. Nutritional data<br />Avoid oils high in saturated fat. <br />Opt for healthier options like sunflower oil!<br />
  14. 14. Manufacture of Alkenes<br />Short-chain alkenes are useful as starting materials for making ethanol and plastics. How can we manufacture alkenes?<br />cracking<br />By __________________ of petroleum<br />Cracking is the _______________ of long-chain hydrocarbons into ___________________.<br />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.<br />breaking down<br />smaller molecules<br />catalyst<br />temperature<br />Cracking<br />
  15. 15. Products of Cracking<br />3 possible types of products<br />Try this:<br />Write an equation for the cracking of heptane (C7H16). (Note: There are a few possible answers)<br />One possible answer: C7H16 C3H6 + C4H8 + H2<br />
  16. 16. Video time: Cracking in the school laboratory<br />3. Describe some characteristics of the gases collected.<br />They have a smell, are flammable and<br />unsaturated (contain C=C bonds).<br />4. Which other test can be used to test for unsaturation?<br />Click here<br />Add acidified potassium permanganate<br />to the unknown. If it turns brown or<br />colourless, the unknown is unsaturated.<br />1. What is the compound that is cracked?<br />Paraffin<br />2. What is the catalyst used?<br />5. Why is the displacement of water<br />method used to collect the products?<br />Pumice stones / broken flower<br />pots<br />The organic products are insoluble in<br />water.<br />
  17. 17. Why the need for cracking?<br /><<br />Shortfall of petrol<br />><br />Excess of fuel oil<br />Cracking of heavier fractions like fuel oil can be used to make up for the shortfall of lighter fractions like petrol.<br />
  18. 18. In short, cracking is used to produce:<br />Hydrogen (fuel and raw material<br />for Haber process)<br />Petrol (fuel)<br />Short-chain alkenes<br />(starting materials for<br />making ethanol and<br />plastics)<br />
  19. 19. Steam cracking adopted<br />Produce large amounts of ethene, propene and butene for making plastics<br />Cracking plants in Jurong island and PulauBukom<br />In the Singapore context<br />Steam cracking plant in Singapore<br />Jurong island<br />PulauBukom<br />
  20. 20. 10 minutes to construct concept maps!<br />Summary<br />1<br />2<br />3<br />Cracking<br />