4.7 CHEMISTRY

• why is oil important

  • It can be used as a fuel
  • it can be made into a plastic
  • ethanol
  • plant oils
  • alkanes and alkenes
• Crude oil


  A finite resource found in Rocks. It is the remains of ancient biomass, consisting of mainly plankton buried in mud. It is a mixture of compounds
• crude oil is mainly made from hydrocarbon, specifically alkanes
• Hydrocarbons 


  Molecules made of hydrogen and carbon atoms only
• Alkanes


  it is a hydrocarbon that is saturated which means all bonds are single bonds
• The alkane formula is 


  $CnH2n+$$2$
• The relationship between boiling and the number of carbon molecules is

  • As the number of carbon atoms increases, the boiling point increases
• This relationship between boiling point and the number of carbon atoms is present because

  when the number of carbon atoms increases a larger chain is formed which have a lot more strong intermolecular forces between them, therefore more energy is required to break those bonds so the boiling point increases
• As the carbon chain length of the hydrocarbon gets bigger, the viscosity and boiling point increases.
• As the carbon chain length of the hydrocarbon gets smaller the flammability increases
• A fractioning column separates part of crude oil
• STEPS FOR FRACTIONAL DISTILLATION

  1. Crude oil is heated in a fractioning tower
  2. The heaviest fraction containing the longest chain hydrocarbon has the highest boiling points. These hydrocarbons don't vaporise and they fall to the bottom of the column
  3. The remaining liquids vaporise
  4. The vapours rise up the fractioning column
  5. The vapours condense at different temperatures. The heavier fractions with long chain hydrocarbons condense first and then the lighter fractions
  6. Very small molecules with the lowest boiling point do not condense and come out at the top of the fractioning column
• Simple distillation summary

  • Heat
  • Evaporate
  • Condense
  • At different temperatures at different boiling points
• Alkenes


  Alkenes are unsaturated hydrocarbons. They are unsaturated because they have double bonds between the carbon atoms. They don't contain the maximum amount of hydrogen atoms
• The first 4 ALKANES

  • Methane
  • Ethane
  • Propane
  • Butane
• The first 4 ALKENES

  • ETHENE
  • PROPENE
  • BUTENE
  • PENTENE
  • Methene does not exist because 2 carbon atoms are required for a double bond
• The Alkene formula is $CnH2N$
• How to test between an alkane and an alkene

  • Using Bromine water an alkene will change the colour of water from orange to colourless
  • An alkane will make the colour of the water remain orange
• The alkene goes back to colourless because since the carbon's have a double bond, they split apart and form a single bond with each bromine molecule, an alkane can't do this as it has single bonds, so it will remain orange
• Cracking is a type of thermal decomposition reaction and 2 products are formed:

  • A saturated alkane with a shorter hydrocarbon chain than the original alkane
  • An unsaturated molecule containing a double bond ( Alkene)
• Cracking requires high temperatures and a catalyst for catalytic cracking or steam for thermal cracking

  High temperatures are required to vaporise the alkane

  
  

  Generally a long-chain hydrocarbon is used because they are not very useful as they are thick liquids and so that shorter hydrocarbons can be produced as they are high in demand good fuels
• ALKENE + HYDROGEN

  • The conditions for this reaction are a nickel catalyst and a temperature of 60 degrees C
  • Propene + Hydrogen = Propane
  • C3H6 + H2 = C3H8
• ALKENE + HALOGEN

  • Conditions, room temperature
  • Pentene + Bromine = Bromopentene
  • C5H10 + BR2 = C5H10BR2
• ALKENE + WATER

  • Conditions: Acid catalyst, high temperatures
  • Ethene + Water = Ethanol
  • C2H4 + H2O = C2H6O
• Alkenes react with water in the presence of acid to give alcohols.
• The general formula for an alcohol is CnH2n+1OH
• Hydrocarbon + oxygen = carbon dioxide + water
• The first 4 alcohols are :

  • Methanol
  • Ethanol
  • Propanol
  • Butanol
• Properties of Alcohols

  1. All alcohols dissolve in water to form a neutral solution(they are soluble)
  2. All alcohols react with sodium to produce hydrogen and a salt (in a beaker you would see bubbles)
  3. All alcohols burn in air to produce CO2 and H2, if it was incomplete combustion it would be carbon monoxide
• Uses of ethanol


  Fuel

  Cleaning products

  Perfume

  Antiseptics

  Drinks
• Making ethanol --> FERMENTATION

  From plant extracts, glucose is extracted. This glucose is mixed with yeast which is a catalyst. And as fermentation is the breaking down of a compound using a biological catalyst, the sugar is broken down into ethanol and carbon dioxide
• Making Ethanol ---> HYDRATION

  • Crude oil is taken to an oil refinery and then the process of fractional distillation occurs which produces an alkane
  • Through the process of cracking an alkene is extracted from the alkane. For example ethene
  • Ethene is then heated at high temperatures with a catalyst (phosphoric acid) and there is a hydration reaction with water
  • Results in ethanol being produced
• Advantages and of fermentation

  • Uses plants as raw materials, which is renewable
• Disadvantages of Fermentation

  • Batch process so it relies on crops being grown in season
  • Produces CO2 which is a greenhouse gas and is bad for the environment.
  • Uses a lot of land to grow crops, which could have been used to feed people
• Advantages of Hydration

  • It is a continuous process which means it can be produced at any point required
• Disadvantages of Hydration

  • Uses a lot of energy which is expensive
  • It uses a product made from crude oil which is a non-renewable resource
• The first 4 carboxylic acids

  • Methanoic acid
  • Ethanoic acid
  • Propanoic acid
  • Butanoic acid
• The general formula for carboxylic acids is CnH2n+1 COOH
• With the process of oxidation, ethanol can be oxidised to ethanoic acid using a chemical oxidising agent
• Carboxylic acids react with carbonates to produce water, carbon dioxide and a salt, this means that carboxylic acids are weak acids as they don't disassociate fully