7 - Organic chemistry

• FRACTIONATING COLUMN

  1. Crude oil is vaporised
  2. The column is hotter at the bottom than the top
  3. The hydrocarbons rise through the column and they condense at their boiling point
  4. Fractions condense at different heights as they have different boiling points

  
• Different alkanes

  
• PRODUCTS OF CRACKING - cracking alkanes will always produce a shorter alkane and at least one alkene.

  
• Different alkenes

  
• Alkenes with halogens - halogens can add to alkenes

  
• ALKENES WITH HYDROGEN

  • React at 150 degrees in the presence of a nickel catalyst
  • Forms alkanes, hydrogenation

  
• ALKENES WITH STEAM

  • High temperature, high pressure and concentrated phosphoric acid as a catalyst
  • Forms alcohols

  
• Alcohols - not hydrocarbons

  
• ALCOHOLS - MILD OXIDATION

  • If alcohols are left in air (oxygen) they will oxidise to form carboxylic acid.

  
• Carboxylic acid examples

  
• Carboxylic acids react with alcohols in the presence of an acid catalyst to form compounds called esters.

  
• A hydrocarbon is a compound made from hydrogen and carbon only. They are covalent compounds since they are made from only non-metal elements. We obtain them from crude oil.
• WHAT IS CRUDE OIL?

  • A mixture of hydrocarbons
  • Made over millions of years out of dead plankton
  • It is an ancient biomass
  • It is a finite resource (non-renewable)
• HOW CRUDE OIL IS FORMED?

  • Plankton
  • Buried in mud
  • Over millions of years
• Alkane general molecular formula: CnH2n+2
• Instead of 3D pictures use a displayed formula as it shows all elements and bonds.
• ALKANES

  • Most common type of hydrocarbons
  • Saturated (full with single covalent bonds) hydrocarbons
• FRACTIONAL DISTILLATION

  Crude oil is a mixture of different length hydrocarbons.

  • So they have different properties
  • So we can separate them using fractional distillation
  • Which separates based on boiling points
• Fraction - A group of hydrocarbons with similar properties
• PROPERTIES OF ALKANES #1 - FLAMMABILITY

  How easily a substance can burn

  • flammability decreases with chain length
  • smaller = more flammable
• PROPERTIES OF ALKANES #2 - CLEANLINESS OF FLAME

  How much smoke or soot is produced

  • cleanliness of flame decreases with chain length
  • smaller = cleaner flame
• PROPERTIES OF ALKANES #3 - BOILING POINTS

  As alkanes get longer, they have stronger intermolecular forces therefore have high boiling points

  • Boiling point increases with chain length
  • Longer = higher boiling point
• PROPERTIES OF ALKANES #4 - VISCOSITY

  How thick (high viscosity) or runny (lower viscosity)

  • viscosity increases with chain length
  • longer = higher viscosity (thicker)
• PROPERTIES OF ALKANES #5 - COMBUSTION

  Most alkanes are fuels, we burn them to release energy

  • Need O2, heat and fuel.
• TYPES OF COMBUSTION - OXIDATION REACTIONS

  1. Complete combustion (plentiful supply of O2)

  • Only products are carbon dioxide and water

  2. Incomplete combustion (limited supply of O2)

  • Only products are carbon monoxide or soot (carbon), carbon dioxide and water
• WHAT IS CRACKING?

  Short hydrocarbons are more useful as fuels because:

  • More flammable
  • Burn with a cleaner flame
  • Release more energy when burnt

  So long chain alkanes are broken down into shorter hydrocarbons by cracking (thermal decomposition reaction(endothermic))
• 2 METHODS OF CRACKING:

  1. Catalytic cracking - heat the long chain alkane with an aluminium oxide (or ceramic pot) catalyst
  2. Steam cracking - heat the long chain alkane with steam
• Alkenes are unsaturated hydrocarbons ( have a carbon carbon double bond)
• Alkenes are more reactive than alkanes because the carbon carbon double bond (which gives it reactivity - functional group) can do various reactions. The carbon carbon double bond breaks open and other substances can then bond to each carbon (addition reaction)
• TESTING FOR ALKENES (UNSATURATED HYDROCARBONS)

  Use bromine water

  Add alkene to bromine water and shake it

  • Should get an addition reaction, colour change

  Alkene - orange -> colourless

  Alkane - no change (stays orange)
• ALKENES WITH OXYGEN

  Burn in oxygen yet we don't burn them as

  • they have smokey flames due to incomplete combustion
  • are valuable - can make polymers / starting materials for other chemicals
• WHAT IS AN ALCOHOL? - NOT A HYDROCARBON

  • An alcohol is a compound using the functional group -OH (on a carbon).
• FORMING ETHANOL

  Fermentation of sugar:

  • sugars are dissolved in water
  • yeast is added
  • mixture is kept warm at approximately 30 degrees
  • air is kept out of the mixture (anaerobic conditions)
• ALCOHOLS - COMBUSTION

  Alcohols burn well in oxygen. They completely combust (form CO2 + H2O).

  methanol + oxygen -> carbon dioxide + water

  2CH4O + 3O2 -> 2CO2 + 4H2O
• ALCOHOLS WITH CARBOXYLIC ACIDS

  • Alcohols react with carboxylic acids (with a catalyst) to form esters.
• ALCOHOLS WITH SODIUM

  • Alcohols react with sodium and produce hydrogen gas
• ALCOHOLS WITH WATER

  • Alcohols do not react, but dissolve in water to form neutral solutions (pH 7)
• USES OF ALCOHOLS

  As fuels burn well. As solvents, medicines and perfumes are made with alcohol. As alcoholic beverages, ethanol -> fermentation, grapes -> wine, apples -> cider, barley -> beer.
• CARBOXYLIC ACIDS

  • Contains the functional group -COOH.
• Carboxylic acids are weak acids as they partially (not 100%) dissociate (H+ ion) in water.