Topic 7 Organic chemistry

• Hydrocarbons

  Contain Carbon and Hydrogen atoms ONLY.
• Alkanes


  All contain C-C single bonds
• Alkanes


  General formula of Cn H2n+2
• Alkanes are saturated molecules

  • Carbon atoms are fully bonded to hydrogen
  • Do not contain any double bonds
  • Carbon contains 4 outer shell electrons therefor can for 4 covalent bonds with other atoms or molecules
• Homologous series

  Alkanes are a homologous series, a group of organic compounds which react in a similar way.
• First 4 Alkanes

  • Methane CH4
  • Ethane C2H6
  • Propane C3H8
  • Butane C4H10
• Properties of hydrocarbons

  • As the chain length increases viscosity increases, very long chain hydrocarbons flow very slowly
  • As chain length increases the molecules become less flammable (combustion), methane is used in bunsen burners
  • Short chain hydrocarbons have low boiling points, all alkanes are gases at room temp
  • As chain length increases the boiling point also increases.
• Combustion of hydrocarbons

  • Ships, planes and cars are all run on hydrocarbon fuels
  • Hydrocarbon fuels release energy when combusted
  • During combustion the carbon and hydrogen atoms in the fuel react with oxygen (They are oxidised)
• Combustion of hydrocarbons

  • If oxygen is unlimited, this produces carbon dioxide and water, called complete combustion
• Crude oil and hydrocarbons

  Plastics, pharmaceuticals, cosmetics, all produced from crude oil.
• Crude oil

  • Produced over millions of years from the remains of plankton buried in mud
  • Found in rocks
  • A mixture of molecules called hydrocarbons
  • finite resource
• Complete combustion


  Methane + oxygen = Carbon dioxide + water

  Propane + oxygen = Carbon dioxide + water
• Fractional distillation of crude oil

  • Each hydrocarbon has a different boiling points
  • Longer chain hydrocarbons have a higher boiling point
  • In order for hydrocarbons in crude oil to be useful we must separate them by fractional distillation into fractions, with similar boiling points and similar number of carbon atoms.
• Fractional distillation

  1. Crude oil is heated to a very high temperature causing the crude oil to boil, all hydrocarbons evaporate and become gaseous
  2. Crude oil vapour is now fed into the fractional distillation column, hotter at the bottom cooler at the top.
  3. Hydrocarbon vapours rise up the column, hydrocarbons will condense when they reach their boiling point, the liquid fractions are then removed
  4. Remaining hydrocarbons continue up the column and condense when they reach their boiling points
• Fractional distillation

  • Very long chain hydrocarbons have very high boiling points, they are removed at the bottom of the column
  • Very short chain hydrocarbons have very low boiling points, they do not condense and are removed from the top of the column
• Uses of fractions

  • Some fractions are used as fuels, eg petrol and diesel for cars, kerosene for jet fuel
  • Kerosene for jet fuel
  • Heavy fuel oil for ships
  • Liquified petroleum gas for camping stoves
• Uses of hydrocarbons

  Feedstock for the petrochemical industry - Chemical used to make other chemicals

  -Solvents

  -Lubricants

  -Detergents

  -Polymers
• Cracking

  • High demand for short chain hydrocarbons to be used as fuels
  • Converting long chain hydrocarbons to short chain hydrocarbons through 'Cracking'
  • In cracking a long chain alkane is broken down (Cracked) to produce smaller more useful molecules
  • Thermal decomposition reaction. (Breaking molecules down by heating)
• Catalytic cracking conditions

  -High temperature (Vapourising)

  -Passed over Catalyst (Speeds up reaction) (Aluminium oxide)
• Steam cracking conditions

  -Vapourise them

  -High temperature

  -Mix them with Steam
• Alkenes and Cracking

  • Cracking makes hydrocarbons called alkenes
  • Alkenes contain a double covalent bond between two carbon atoms
  • Alkenes are used to make chemicals called polymers
  • Alkenes are used as the starting material for other useful chemicals
  • Alkenes are more reactive than alkanes
• Testing for alkenes

  • Using Bromine water, which is orange
  • If we shake the alkene with bromine water, it turns colourless
• Cracking equations


  Long chain hydrocarbon molecule (Decane 10 C atoms) = Shorter alkane molecule (Octane 8 C atoms) + Alkene (Ethene 2 C atoms) for making plastics.

  Same number of Hydrogen and carbon atoms on both sides of the equation.
• Alkenes


  General formula Cn H2n
• Alkenes are unsaturated molecules

  • Alkenes have 2 fewer hydrogen atoms than the alkane with the same number of carbon atoms, the carbon atoms are not fully bonded
  • They contain a covalent C=C double bond
• First 4 alkenes

  • Ethene C2H4
  • Propene C3H6
  • Butene C4H8
  • Pentene C5H10
• Reactions of Alkenes

  • Alkenes all react similarly due to the C=C double bond which is the Alkene "Functional group"
• Functional groups

  • Members of a homologous series all have the same functional group
  • The part of a molecule that determines its reaction/how it reacts
• Combustion of alkenes

  • Produces carbon dioxide and water, with alkenes we also produce unburnt carbon particles along with carbon monoxide (a poisonous gas) due to incomplete combustion
  • Alkenes burn in air with a smoky yellow flame (incomplete combustion)
  • Combust completely in a large amount of oxygen
  • Often undergo incomplete combustion
• Reactions of Alkenes

  • Alkenes react via Addition reactions
  • All react similarly due to the functional group C=C.
  • In addition reactions the carbon=carbon bond will often open up and a new atom is added to each carbon.

  
• Addition of Hydrogen (Hydrogenation)

  Hydrogen can react with the double bonded carbons to open up the double bond and form the equivalent, saturated, alkane. The alkane is reacted with hydrogen in the presence of a nickel catalyst and at 150 degrees. Ethene is converted to ethane

  
• Hydration

  • Steam can react with alkenes to form alcohols
  • When alkenes react with steam water is added across the double bond and an alcohol is formed
  • For example, ethanol can be made by mixing ethene with steam and then passing it over a phosphoric acid catalyst.
  • Temp of 300 degrees and 70 atmospheres of pressure
  • Reversible reaction, to increase yield of ethanol any unreacted ethene and steam are passed back through the catalyst and recycled back.
• Alkenes reacting with halogens.

  • Alkenes will also react in addition reactions with halogens such as bromine, chlorine and iodine, the molecules formed and saturated with the C=C carbons each becoming bonded to a halogen atom.
  • For example bromine and ethene react to form dibromoethane. (Bromine has 2 atoms)
• Alcohols

  • General formula of an alcohol is Cn H2n+1 OH
  • Alcohols contain an -OH functional group
  • Homologous series
• First 4 Alcohols

  • Methanol CH3OH
  • Ethanol C2H5OH
  • Propanol C3H7OH
  • Butanol C4H9OH
• Alcohols uses

  • Fuels
  • Solvents
  • Alcoholic drinks
  • Functional group OH
• First 4 alcohols have similar properties

  • Alcohols are flammable. They undergo complete combustion in air to produce carbon dioxide and water.
  • Eg 2CH3OH+302=2C02+4H20
• Alcohols

  • First 4 alcohols are all soluble in water, their solutions have a neutral pH
  • They can react with sodium one product being hydrogen
  • Alcohols can be oxidised by reacting with oxygen to produce a carboxylic acid
  • Different alcohols form different carboxylic acids eg methanol is oxidised to methanoic acid
• Alcohols

  • Alcohols such as methanol and ethanol are used as solvents in industry, because they can dissolve most things water can dissolve but can also dissolve substances such as hydrocarbons, oils and fats.
  • The first 4 alcohols are used as fuels. Eg ethanol is used as a fuel in spirit burners.
• Alcohols can be made by fermentation

  • Ethanol is the alcohol found in alcoholic drinks such as wine or beer. It's usually made using fermentation
  • Fermentation uses an enzyme in yeast to convert into ethanol. Carbon dioxide is also produced, The reaction occurs in solution so the ethanol produced is aqueous