2022

• A colour will stay on the start line if

  It is insoluble in the solvent
• What process can be used to produce potable water from salty water

  Distillation
• Why is the mass of the conical flask and content greater at the start of the reaction than end

  sulfur dioxide is produced which escapes from the conical flask.
• hydrocarbon D-

  molecules made up of carbon and hydrogen atoms only.
• why one of the products of cracking is in high demand

  more useful as a fuel,more flammable than larger molecules. because more reactive than alkanes.
• Type of substance is a catalyst in biological systems

  enzyme
• Q1.1 A student investigated the colours in a brown ink using chromatography.Figure 1 shows the apparatus used.Give two errors made by the student.Describe the problem each error would cause. (4 marks)

  Error 1:

  • The start line was drawn in ink
  • Problem 1:
  • The ink from the line will dissolve in the solvent and interfere with the results

  Error 2:

  • The solvent level is above the start line
  • Problem 2:
  • The ink spots will dissolve into the solvent, ruining the separation of colours
• Q1.2 Give two conclusions the student can make from Figure 2 about the four colours in the brown ink. (2 marks)A:

  • The brown ink contains blue, yellow, and red colours
  • The brown ink does not contain green ink
  • OR
  • The brown ink contains an unknown colour (not matching any reference)
  • The red colour is least soluble (moved the least)
• Water that is safe to drink is called potable water.Compare how easily potable water can be obtained from:

  • waste water (sewage)

  • ground water (fresh water)(6 marks)

  A:

  Ground Water:

  • Easier to obtain
  • Fewer processes
  • Takes less time
  • Filtered through filter beds to remove insoluble particles
  • Sterilised using chlorine, ozone, or UV light to kill bacteria

  Waste Water:

  • More difficult to obtain
  • More processes
  • Takes more time
  • Screening and grit removal to remove large particles
  • Sedimentation to produce sewage sludge and effluent
  • Aerobic biological treatment of effluent to reduce solid waste
  • Then sterilised using chlorine, ozone, or UV light to kill bacteria
  • Sludge is anaerobically digested by specific bacteria to remove organic matter
• Q: Evaluate the sustainability of wooden and plastic window frames.You should include environmental and economic factors. (6 marks)

  A:

  Environmental Factors:

  • Plastic frames release more greenhouse gases during production and disposal, contributing more to global warming than wooden frames
  • They produce more oxides of nitrogen and sulfur dioxide, leading to acid rain
  • Plastic frames use more hydrocarbons (non-renewable) compared to wood (renewable)
  • Plastic production creates more waste and requires more energy to produce and dispose of

  Economic Factors:

  • Plastic frames have lower lifetime and maintenance costs
  • This is beneficial to customers as it saves money long-term
  • Wooden frames are more expensive due to higher maintenance and lifetime cost

  Conclusion:

  • Overall, wooden frames are more environmentally sustainable
  • But plastic frames are more cost-effective and may be preferred for economic reasons
• Q: After the formation of the Earth’s early atmosphere, the amounts of nitrogen and oxygen in the atmosphere changed.Explain the main changes in the amounts of nitrogen and oxygen in the Earth’s atmosphere. (4 marks)A:

  • Nitrogen concentration increased in the atmosphere because nitrogen gas was released through volcanic activity
  • Oxygen concentration increased later as photosynthetic algae and plants evolved and started producing oxygen
• Q: Describe how coal was formed from the carbon dioxide present in the Earth’s early atmosphere. (4 marks)A:

  • Carbon dioxide was taken in by photosynthesising plants, such as trees
  • When the trees died, they were buried under layers of sediment
  • Over millions of years, high pressure and heat caused by sediment compression acted on the plant remains
  • The organic matter from the trees was converted into coal
• Q: The combustion of 1.0 kg of coal produces more carbon dioxide than the combustion of 1.0 kg of natural gas.Suggest why. (1 mark)A:

  • Coal has a higher proportion of carbon than natural gas
• : Describe how bioleaching is used to extract copper from low-grade ores. (3 marks)A:

  • Bacteria is used to convert copper compounds in the ore into a solution
  • The solution still contains copper compounds
  • The solution is then used in electrolysis to extract pure copper from the compounds
• Explain how a catalyst increases the rate of a reaction. (2 marks)A:

  • A catalyst provides an alternative reaction pathway that requires less activation energy
  • This means more particles will have enough energy to successfully collide and react
• : What can scientists predict using Le Chatelier’s Principle? (1 mark)A:

  • How changing conditions affect the position of equilibrium
• Q: Describe how a reversible chemical reaction is able to reach equilibrium. (2 marks)A:

  • In a closed system where no products or reactants can enter or leave, the forward and backward reactions happen at the same rate
  • This balance means the concentrations of reactants and products remain constant
• Q: Explain the effect of increasing the pressure on the yield of ammonia. (2 marks)A:

  • Increasing pressure increases the yield of ammonia
  • Because there are fewer gas molecules on the right-hand side of the equation (2 NH₃ vs. 4 reactant molecules)
• Q: Explain the effect of increasing the temperature on the yield of ammonia. (2 marks)A:

  • The yield of ammonia decreases
  • Because the system shifts in favour of the endothermic (reverse) reaction