Unit 2 - The World of Carbon

Fuels
1. Petrol
  1. made from reforming the naptha fraction (fractional distillation of crude oil)
  2. hydrocarbon - 5 to 10 carbons in a chain
  3. summer - less volatile hydrocarbons to stop it evaporating too quickly
  4. winter - more volatile hydrocarbons to make it evaporate more quickly
    1. small molecules are more volatile
  5. Petrol Engine
    1. combustion of petrol produces hot gases that expand against parts of the engine - causing them to move
      1. waste gases - carbon dioxide, carbon monoxide, nitrogen oxides & water vapour
    2. Knocking
      1. combustion of petrol-air mixture is triggered by a spark
        fuel can auto-ignite out of sequence (pre-ignition)
        reduces engine performance
        octane number - measure of a fuel's ability to resist knocking
        high octane number less likely to cause knocking
        using branched alkanes, aromatic hydrocarbon or cycloalkanes prevents knocking (in the past lead was used but it was damaging to the environment)
  6. Reforming
    1. alters the arrangement of atoms in a molecule without necessarily changing the no. of carbon atoms per mollecule
      1. can change straight chain alkanes into branched-chain alkanes, cycloalkanes, cycloalkanes & aromatic hydrocarbons
        e.g. heptane to methylbenzene
2. Alternative Fuels
  1. Biofuels
    1. fuels made from plant or animal matter
    2. Ethanol
      1. made from the fermentation of sugars
      2. pros: high octane number, very clean burning, liquid
      3. cons: expensive, lots of land needed to grow sugar cane which some climates are unsuitable for
    3. Methane
      1. produced by the anaerobic respiration of plant & animal waste
      2. pros: more harmful than carbon dioxide for greenhouse effect but when burnt converts to less harmful substances, renewable
      3. cons: must be stored in high pressure cylinders - dangerous in a crash
    4. Methanol
      1. produced from the reaction of methane and steam
      2. pros: clean burning, liquid, high octane number
      3. cons: very corrosive, very toxic
  2. Hydrogen
    1. made from the electrolysis of water
    2. pros: renewable, when environmentally friendly ways of providing energy for electrolysis it is completely green, product of combustion is water which can be reused to make more hydrogen
    3. cons: stored under high pressure which is expensive and dangerous, is highly flammable
Carbon Compounds
1. Alkanes
  1. Cn H2n+2
  2. straight chain but can be branched or bent
2. Alkenes
  1. Cn H2n
  2. C=C bond
  3. when naming count from the side with the C=C
3. Alkynes
  1. Cn H2n-2
  2. C to C triple bond
4. Alkanols
  1. alcohol, functional group OH (hydroxyl group)
  2. Primary Alcohols
    1. OH at end of the molecule
      1. oxidises (acidified potassium dichromate) into an aldehyde
        then oxidised to a carboxylic acid
        e.g. propan-1-ol to propanal to propanoic acid
  3. Secondary Alcohol
    1. OH in the middle of the molecule
      1. oxidised into a ketone
        NO FURTHER REACTION
        e.g. propan-2-ol to propanone
  4. Tertiary Alcohol
    1. DOES NOT OXIDISE
      1. oxidising agent take the hydrogen from the OH group and the hydrogen from the carbon attached to the OH group - tertiary alcohols do not have a hydrogen attached to that carbon
5. Aldehydes & Ketones
  1. functional group: the carbonyl group C=O
  2. Aldehydes
    1. known as alkanals & have the C=O group at the end of the molecule
  3. Ketones
    1. known as alkanones & have a C=O bond in the middle of a molecule
6. Carboxylic Acids
  1. carboxyl group: COOH
  2. carboxyl group always at the end of the molecule
7. Esters
  1. condensation reaction or esterification: ALCOHOL = ALKANOIC ACID =/= ESTER = WATER
  2. alcohol is first part of name, acid is second e.g methanol = ethanoic acid = methyl ethanoate
  3. ester link
  4. used as flavourings, chemicals & solvents
8. Aromatic Hydrocarbons
  1. benzene, C6H6
    1. delocalised electrons make it very stable - resistant to addition reactions
    2. does not decolourise bromine solution as it has no C=C
  2. a benzene ring in which one of the hydrogen atoms has been substituted by another group is known as the phenyl group
Reactions of Carbon Compounds
1. Addition
  1. alkenes undergo addition reactions to form saturated compounds
    1. addition of hydrogen is known as hydrogenation
      1. addition of halogens forms halogenoalkanes
        addition of water is called hydration
2. Dehydration
  1. removal of water
    1. alcohols can be converted into alkenes by dehydration
3. Oxidation
  1. loss of oxygen
    1. oxidising agents
      1. acidified potassium dichromate solution: orange to green
        Tollens Reagent: colourless to silver mirror
        Fehlings solution: blue to orange
        Copper (II) oxide (solid)
  2. complete oxidation is combustion
    1. burning a hydrogen compound in a poor supply of oxygen will make a poisonous gas CO
4. Reduction
  1. gain of oxygen
    1. aldehydes & ketones can be reduced back to their corresponding alcohol
Polymers
1. Plastics & Fibres
  1. addition polymers - when small unsaturated molecules like ethene form polymers like poly(ethane) by addition polymerisation
    1. ethene is an important feedstock in the petrochemical industry - especially the manufacture of plastics
      1. ethene is made from cracking of the naptha fraction
  2. condensation polymers - made from monomers with 2 functional groups per molecule
    1. polyesters - contain the ester link
      1. polyester fibre is a thermoplastic linear polymer, the polymer chains have weak van der Waals forces between them which can be easily broken
        polyester resin has strong covalent cross links between polymer chains, this forms a rigid 3D structure which is not easily broken on heating - thermosetting plastic
  3. Polyamides
    1. formed be the condensation of a di-amide & a di-acid
      1. amines contain the amino function group NH2
        repeating units of polyamides are held together by amide links
    2. nylon is a polyamide
      1. it is so strong because of hydrogen bonding between the chains
2. Thermosetting & Thermoplastic Plastics
  1. Thermoplastic
    1. can be melted/shaped many times
      1. when a thermoplastic polymer is heated the chains are free to move away from each other
  2. Thermosetting
    1. thermosetting polymers don't melt due to cross-links between chains so they can't move away from each other
      1. Methanal
        feedstock in the manufacture of thermosetting plastics
        steam reforms methane or coal to make synthesis gas (CO & H) which is converted to methanol which is oxidised to methanal
        Bakelite & melamine are made from methanal & have a 3D cross-link network structure
        Urea-methanal has many cross-links which are almost impossible to separate & does not melt on heating
3. Recent Developments
  1. Kevlar: aromatic polyamide, v. strong due to rigid linear polymer chains joined with hydrogen bonds, light, waterproof, fireproof
    1. Poly(ethanol): soluble in water, used for laundry bags in hospitals to prevent contact with infected material, ester exchange allows for H's to be replaced with OH's which makes it soluble
      1. Poly(ethyne): addition polymerisation of ethyne molecules, conducts electricity when a dopant'
        Poly(vinyl carbazole): addition polymer made from vinyl carbozole, conducts electricity when light shines on it (photoconductivity), used for photocopiers
        Biopol: natural polyester, biodegradable
        Photodegradable low-density poly(ethene): low-density poly(ethene) is modified to produce a photodegradable polymer - will degrade on exposure to ultra-violet light
Natural Products
1. Fats & Oils
  1. animal(lard), vegetable(olive oil), marine(fish oil)
  2. esters made through the condensation between propane- 1, 2, 3-triol (glycerol) & fatty acids
    1. fatty acids are saturated or unsaturated straight chain carboxylic acid e.g. stearic acid & oleic acid
    2. glycerol is a trihydric alcohol which means it has 3 hydroxyl groups & will form 3 ester links with 3 fatty acid molecules
      1. the ester formed from glycerol is known as glyceride - fats & oils are called triglycerides
  3. fats have a higher melting point than oils because they are made up of saturated fatty acid chains which allow for closer packing and van der Waals forces
    1. oils are made up of unsaturated fatty acid chains which are bent due to the double bonds which prevents the chains from packing cloely together
  4. oils can be converted into fats by the addition of hydrogen across the C=C, this is called hardening, the reaction uses a nickel catalyst & is an example of hydrogenation
  5. when fats & oils are hydrolysed 1 mole of glycerol & 3 moles of fatty acids will be produced
2. Proteins
  1. condensation polymers of many amino acid molecules joined together
    1. amino acids have functional groups: carboxyl & amino
      1. 2 amino acids make a dipeptide, 3 make a tripeptide & many make a polypeptide or a protein
  2. tripeptide formation: the peptide (amide) link is formed in a reaction between carboxylic acids & the amino group
    1. the body can produce most of the amino acids needed to make the proteins required by the body but some can't be made by the body & must be acquired through diet - essential amino acids
  3. Digestion
    1. during digestion proteins are hydrolysed into their original amino acids
      1. the proteins by the body are built up from the amino acids in the bloodstream
  4. Types of protein
    1. fibrous proteins are long & thin & are the major structural materials of animal tissue e.g. keratin in hair & collagen in tendons
      1. globular proteins have spiral chains folded in a compact shape & are involved in maintenance & regulation of life processes e.g. hormones (insulin) & haemoglobin
  5. enzymes
    1. biological catalysts
      1. specific to substrates - shape of active sites
        they work best within narrow temperature & pH ranges & outwith these ranges become denatured
3. Soaps
  1. soaps made from fat/oil by alkaline hydrolysis
    1. reacted with NaOH
  2. hydrocarbon tail dissolves other liquids with hydrocarbon chains e.g. oil
    1. ionic head dissolves in the water
      1. negative charged surfaces of grease globules repel each other

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Unit 2 - The World of Carbon

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