Topic 7- Organic Chemistry

• What atoms do hydrocarbons contain?

  Hydrogen and Carbon atoms
• What bonds do alkanes have?

  Single bonds
• What is the formula for alkanes?

  CnH2n+2
• What does homologous series mean?

  A group of organic compounds that react in a similar way.
• What are saturated compounds?

  Each carbon atom will for 4 single covalent bonds
• What properties do alkanes have?

  Saturated hydrocarbons, Homologous series
• What are the first 4 alkanes?

  Methane, ethane, propane, butane.
• What physical properties does a short alkane chain have?

  Low boiling point, less viscous (more runny), more flammable
• What is the word equation for complete combustion of a hydrocarbon in oxygen?

  Hydrocarbon + oxygen -> carbon dioxide + water (+energy)
• During combustion, the carbon & hydrogen from the hydrocarbon are what?

  Oxidised
• What is the balanced symbol equation of hydrocarbon fuel combustion?

  CH4 + 2O2 -> CO2 + 2H2O
• What is crude oil?

  A fossil fuel- remains of plants, animals and plankton from millions of years ago
• What is fractional distillation used for?

  Separating mixtures - crude oil
• How does fractional distillation work for crude oil?

  Oil is heated until it is a gas which enters a fractionating column.

  In the fractioning column, the bottom is hot and the top is cool.

  Long hydrocarbons condense into liquids at the bottom, short hydrocarbons at the top.

  The crude oil mixture is now seperated.
• What is one use for crude oil?

  Fuel for transport.
• What does cracking of crud oil mean?

  Splitting up long-chains of hydrocarbons
• What is used to test for alkenes?

  Bromine water
• What colour does the bromine water turn after testing for alkenes?

  Orange to colourless.
• What type of reaction is cracking?

  Thermal decomposition
• What is thermal decomposition?

  The breaking down of molecules by heating them.
• What is the process of thermal decomposition with hydrocarbons?

  Heat the long chain of hydrocarbons to vaporise them (turn them into gas)

  Vapour is passed over a hot powdered aluminium oxide catalyst.

  The long chain molecules split apart on the catalyst's surface (catalytic cracking).
• What is steam cracking?

  Process of breaking down hydrocarbon molecules in the presence of steam to produce smaller molecules, such as ethylene and propylene.
• What is an alkene?


  A hydrocarbon that has a double bond between 2 carbon atoms
• What bond does an alkene have?

  A double bond which means that they have 2 fewer hydrogen atoms than alkanes, which make them unsaturated
• Is an alkene or alkane more reactive?

  Alkenes - the double bond can open up to make a single bond, which allows carbon to bond with other atoms
• What are the first 4 alkenes?


  Ethene (2 carbon)

  Propene (3 carbon)

  Butene (4 carbon)

  Pentene (5 carbon)
• What is the general formula for alkenes?

  CnH2n
• What happens when you burn alkenes in large amounts of oxygen?

  Complete combustion which produces carbon dioxide and water
• What happens when you burn alkenes in normal amounts of oxygen?

  Incomplete combustion (there normally isn't enough oxygen in the air to combust completely)
• What is the word equation for incomplete combustion for alkenes?


  Alkene + oxygen → carbon + carbon monoxide + water
• What is the result of incomplete combustion with alkenes?


  Produces a smoky, yellow flame and less energy is released
• What is a functional group?


  A group of specific atoms in a molecule that determine how that molecule typically reacts
• What is the functional group in alkenes?

  C = C
• What is an addition reaction?


  An alkene reaction- the carbon double bond will open up to leave a single bond where a new atom is added to each carbon
• What is the addition of hydrogen called?

  Hydrogenation
• What happens when hydrogenation happens with an alkene?


  In the presence of an alkene, the hydrogen can react with the double-bonded carbons to open up the double bond and form the saturated alkane
• What bonds to alkanes have?

  Single carbon bonds- saturated
• What happens when steam reacts with alkenes?

  An alcohol is formed- e.g. ethanol is made by mixing ethene with steam and passing it over a catalyst
• How do you make ethanol?


  -reaction happens between steam and ethene over a catalyst

  -reaction mixture is passed into a condenser

  -ethanol and water have a higher boiling point than ethene so both condense

  -any unreacted ethene gas is recycled back into reactor

  -alcohol can be purified by fractional distillation
• How do halogens react with alkenes?


  The molecules formed are saturated with each bond becoming bonded to a halogen atom