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StarterHow many fractions can you name from the        fractionating column ?                In order          Without loo...
alkenesalkenes a group of hydrocarbons with the general formula, CnH2n  where n is the number of carbon atoms in one mole...
alkenesalkene homologous series each member of the series differs from the next by an  extra –CH2- group of atoms   No. o...
alkenesreactions of alkenes: combustion alkenes burn in air to form CO2 and H2O incomplete combustion results in the for...
alkenesreactions of alkenes: addition reactionsAlkenes undergo addition reactionThis means that a molecule is added to t...
H   HH   C   C   H    X   X
alkenesreactions of alkenes: addition reactions addition of bromine (bromination)  o   bromine molecule adds to the C=C b...
H    HH   C    C    H    Br   Br
alkenesreactions of alkenes: addition reactions addition of hydrogen (hydrogenation)  o alkenes react with hydrogen to pr...
H   HH   C   C   H    H   H
alkenesreactions of alkenes: addition reactions addition of water (hydration)  o alkenes react with steam over a catalyst...
H   HH   C   C    H    H   OH
alkenessaturated and unsaturated hydrocarbons alkanes are saturated because it is not possible to add extra  atoms to the...
alkenes  saturated and unsaturated hydrocarbons differences between saturated and unsaturated hydrocarbons:        Satura...
alkenestesting for unsaturated compoundslike alkenes for liquids: add a solution of bromine in water to an alkene  and sh...
alkenestesting for unsaturated compoundslike alkenes for gas: bubble the gas through a solution of bromine in  water; col...
Demo - to distinguish between an alkane and an alkene               (decolourisation of bromine!).                   hexen...
Qn: What will happen if I bubble the gas from a bottle filled with bananas to                            the bromine water?
Demo – while ripening, bananas give off ethene gas!              bananas                           bananasbromine         ...
manufacture of alkenescrackingAlkene molecules can be made by cracking alkanes a process to break up big alkane molecule...
cracking of alkanescracking           C20H42     C12H26 + C8H16              big     an alkane   an alkene            alka...
cracking of alkanescracking Uses:   Hydrogen can be one of the products in the cracking of   alkanes          C16H34     ...
cracking of alkanescracking Uses: o   cracking of big petroleum molecules into smaller      hydrocarbon molecules to prod...
polymerspolymerisationMacromolecules are very large numbers of small moleculesjoined together.Polymerisation is the chemic...
polymerspolyethene (polythene) one of the simplest addition polymer used to make ‘cling film’ for wrapping fresh vegetab...
polymerspolyethene (polythene) deriving the polymerisation equation:  o write out the structural formulae of several ethe...
polymerspolyethene (polythene) deriving the polymerisation equation:  o join the molecules together       H   H   H   H  ...
polymersexamples of addition polymer  Chemical Name of                      Monomer   Polymer                    Uses     ...
unsaturated foods polyunsaturatedmeans that organic molecules contain C=C  bonds example: vegetable oils are polyunsatur...
Demo - Testing for unsaturation          bromine
After five droplets of each to bromine solution, shaken and stirred…            butter       margarine         ghee       ...
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G10alkenes

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G10alkenes

  1. 1. StarterHow many fractions can you name from the fractionating column ? In order Without looking 
  2. 2. alkenesalkenes a group of hydrocarbons with the general formula, CnH2n where n is the number of carbon atoms in one molecule contain the C=C functional group (unsaturated hydrocarbons) names of alkenes end with -ene are molecular compounds have low boiling points; gases under room conditions a ball-and-stick model of ethene, C2H4
  3. 3. alkenesalkene homologous series each member of the series differs from the next by an extra –CH2- group of atoms No. of Carbon Relative Boiling Alkene Structure of One Atoms in One Molecular Point Member Molecule Molecule Mass (°C) H H ethene 2 28 C C -104 (C3H4) H H H H propene 3 42 H C C C -48 (C3H6) H H H H H H butene 4 56 H C C C C -6 (C4H8) H H H H
  4. 4. alkenesreactions of alkenes: combustion alkenes burn in air to form CO2 and H2O incomplete combustion results in the formation of carbon monoxide, CO and soot, C alkenes tend to produce more soot than alkanes when they burn in air  example: combustion of ethene C2H4 + 3O2 2CO2 + 2H2O
  5. 5. alkenesreactions of alkenes: addition reactionsAlkenes undergo addition reactionThis means that a molecule is added to the alkene to makeone productThis is possible because of the carbon-carbon double bond(C=C ) in an alkene.
  6. 6. H HH C C H X X
  7. 7. alkenesreactions of alkenes: addition reactions addition of bromine (bromination) o bromine molecule adds to the C=C bond of ethene molecule o example: addition reaction of bromine to ethene C2H4 + Br2 C2H4Br2 H H H C Br H C Br + C Br H C Br H H H reaction with aqueous bromine is used as a test for alkenes and other unsaturated compounds alkene is shaken with or bubbled through a solution of bromine in water; alkene quickly decolourises the reddish- brown bromine solution
  8. 8. H HH C C H Br Br
  9. 9. alkenesreactions of alkenes: addition reactions addition of hydrogen (hydrogenation) o alkenes react with hydrogen to produce alkanes in the presence of nickel metal (catalyst) o example: addition reaction of hydrogen to ethene o hydrogen molecule adds to the C=C bond of ethene molecule used in producing margarine from vegetable oil C2H4 + H2 C2H6 H H H C H H C H + C H H C H H H H
  10. 10. H HH C C H H H
  11. 11. alkenesreactions of alkenes: addition reactions addition of water (hydration) o alkenes react with steam over a catalyst to produce alcohols o example: addition reaction of water to ethene C2H4 + H2O CH3CH2OH H H H C OH H C OH + C H H C H H H H o water molecule adds to the C=C bond of ethene molecule alcohols are commonly used as solvents and to make other chemicals
  12. 12. H HH C C H H OH
  13. 13. alkenessaturated and unsaturated hydrocarbons alkanes are saturated because it is not possible to add extra atoms to their molecules alkenes are unsaturated because extra atoms can be added to their molecules in addition reactions H H H H H C C H H C C H H H
  14. 14. alkenes saturated and unsaturated hydrocarbons differences between saturated and unsaturated hydrocarbons: Saturated Hydrocarbons Unsaturated Hydrocarbons Contains carbon-carbon single Contains carbon-carbon bonds (C-C) double bonds (C = C) Extra atoms not added to their Extra atoms added to their molecules in addition molecules in addition reactions reactions have alkane-type formula of have alkene-type formula of CnH2n+2 CnH2n Reaction with aqueous bromine Reaction with aqueous bromine : : do not decolourise aqueous decolourises aqueous bromine bromine
  15. 15. alkenestesting for unsaturated compoundslike alkenes for liquids: add a solution of bromine in water to an alkene and shake them; reddish-brown colour of bromine disappears in the presence of alkene liquid alkene bromine bromine solution becomes colourless shake testing for liquid alkene
  16. 16. alkenestesting for unsaturated compoundslike alkenes for gas: bubble the gas through a solution of bromine in water; colour of bromine disappears in the presence of alkene gas gaseous alkene bromine poly(ethene) bromine solution becomes colourless testing for gaseous alkene
  17. 17. Demo - to distinguish between an alkane and an alkene (decolourisation of bromine!). hexene hexanehexane hexene bromine bromine
  18. 18. Qn: What will happen if I bubble the gas from a bottle filled with bananas to the bromine water?
  19. 19. Demo – while ripening, bananas give off ethene gas! bananas bananasbromine bromine
  20. 20. manufacture of alkenescrackingAlkene molecules can be made by cracking alkanes a process to break up big alkane molecules into smaller molecules; done by passing big alkane molecules over a solid catalyst at a high temperature example: cracking of big petroleum (hydrocarbon) molecules CATALYST hydrocarbon molecules big hydrocarbon break up on the small hydrocarbon molecules surface of the catalyst molecules
  21. 21. cracking of alkanescracking C20H42 C12H26 + C8H16 big an alkane an alkene alkane molecule molecule C18H38 X + C10H20 big an an alkane ________ ________ molecule molecule
  22. 22. cracking of alkanescracking Uses: Hydrogen can be one of the products in the cracking of alkanes C16H34 H2 + C6H12 + C10H20 Hydrogen is used as fuel for big rockets and to make ammonia for fertilisers
  23. 23. cracking of alkanescracking Uses: o cracking of big petroleum molecules into smaller hydrocarbon molecules to produce fuel for motor vehicles; • This is important as the amount of petrol produced from fractional distillation of petroleum is insufficient. So the extra petrol needed is produced by cracking
  24. 24. polymerspolymerisationMacromolecules are very large numbers of small moleculesjoined together.Polymerisation is the chemical reaction when large numbersof similar small molecules (monomers) are joined togetherto form a big molecule (polymer). H HH HH H H HH H H H H H H H C C C CC CC C CC CC C C C H H H H H H H HH HH H H HH H
  25. 25. polymerspolyethene (polythene) one of the simplest addition polymer used to make ‘cling film’ for wrapping fresh vegetables and meat, plastic bottles, plastic bags, buckets and pipes can be made up of 500 to 20,000 ethene molecules hydrogen atom carbon atom model of polyethene molecule
  26. 26. polymerspolyethene (polythene) deriving the polymerisation equation: o write out the structural formulae of several ethene molecules in a row H H H H H H H H H H C C C C C C C C C C H H H H H H H H H H o open the C=C double bonds H H H H H H H H H H C C C C C C C C C C H H H H H H H H H H
  27. 27. polymerspolyethene (polythene) deriving the polymerisation equation: o join the molecules together H H H H H H H H H H H H C C C C C C C C C C C C H H H H H H H H H H H H formula of polyethene can be simply written as: H H C C H H n
  28. 28. polymersexamples of addition polymer Chemical Name of Monomer Polymer Uses Polymer H H H H Plastic film for wrapping Poly(ethene) fresh vegetables and meat; C C C C or polythene plastic bottles; plastic H H H H n bags, buckets and pipes H Cl H Cl Poly(chloroethene) For water pipes, waterproof C C C C plastic sheet, insulation for or PVC electric cables and wires H H H H n For packaging and H C6H5 H C6H5 containers for electrical Poly(phenylethene) C C C C goods, disposable cups and or polystyrene food containers used in H H H H n ‘fast food’ restaurants and hawker centres
  29. 29. unsaturated foods polyunsaturatedmeans that organic molecules contain C=C bonds example: vegetable oils are polyunsaturated oils manufacture of margarine by addition reaction; vegetableoil reacts with hydrogen in presence of nickel catalyst; H2 molecules add to the C=C bonds of vegetable oil after addition reaction, vegetable oil has more hydrogen atoms and hence, greater relative molecular mass and higher melting point; becomes solid(solidify) at room conditions margarine (a healthy product) made from vegetable oil by addition reaction
  30. 30. Demo - Testing for unsaturation bromine
  31. 31. After five droplets of each to bromine solution, shaken and stirred… butter margarine ghee olive oilButter - did not decolorized Br soln (very minimal) - mostly saturatedMargarine - decolorized Br soln (largely) - mostly polyunsaturatedGhee - did not decolorized Br soln(least) - highly saturatedOlive oil -decolorized Br soln(completely) - highly monounsaturated

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