6 markers

• Fractional distillation

  1. The column is hotter near the bottom and cooler near the top
  2. Crude oil is heated
  3. Hydrocarbons evaporate (liquid → gas)
  4. Hydrocarbons condense at different points
  5. Short hydrocarbons have low boiling points and condense near the top
  6. Long hydrocarbons have high boiling points and condense near the bottom
  7. Bitumen longest hydrocarbon remains liquid and comes out of the bottom
• Catalytic Cracking

  1. Hydrocarbon are heated and vaporized
  2. Powdered aluminium oxide catalyst is heated
  3. Hydrocarbon vapors are passed over the catalyst
  4. Long hydrocarbons chains break down into smaller chains
  5. Break down using heat = thermal decomposition
  6. Short hydrocarbon chains are released and collected
• Rate of reaction - volume of gas practical

  1. Place reactants in conical flask (HCl + Mg) and close with bung
  2. Attach gas syringe (fully pushed in so there are no gas leaks)
  3. Measure volume of gas produced over a given time (e.g. 2 mins)
  4. Plot gas produced (cm?) against time (s) on a graph
  5. Reaction is complete from time when no more gas is produced
  6. Repeat with different variables and compare rates
• Rate of reaction - disappearing cross practical

  
  

  1. Mix reactant solutions into a flask placed over a white tile with a cross
  2. Start stopwatch and keep an eye on the cross as precipitate forms
  3. Stop stopwatch and record time taken for cross to disappear
  4. Repeat experiment for different concentrations of HCI
  5. Plot graph of time taken vs different concentrations of HCI

  6. At higher concentrations, less time taken for reaction to complete
• Haber process - compromise conditions

  1. The forward reaction is exothermic, so low temperatures increase yield of ammonia.
  2. However, low temperatures slow the rate
  3. A compromise temperature of 450 °C is used to give a reasonable yield and rate.
  4. The forward reaction produces fewer gas molecules
  5. Higher pressure favours forward reaction yield
  6. Too much pressure is costly and dangerous for equipment
  7. A compromise pressure of 200 atm is chosen to balance yield, rate, and safety.