Six-mark questions

Six-mark questions are extended open response questions. These require longer answers than the structured questions. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.

To gain full marks you need to:

  • support explanations using scientific knowledge and understanding
  • use appropriate scientific words and terms
  • write clearly and link ideas in a logical way
  • maintain a sustained line of reasoning, rather than getting lost or bogged down

Six-mark questions often use these command words:

  • describe - you need to give an account but no reason
  • explain - you must give reasons or explanations
  • devise - you must plan or invent a procedure using your scientific knowledge and understanding
  • evaluate - you must review information, including identifying strengths and weaknesses, and make a supported conclusion

Six-mark questions may be synoptic questions. These questions bring together ideas from two or more topics. For example, a question about fertilisers could include ideas about covalent substances, acids and alkalis, chemical calculations and effects on the environment.

The answers shown here give marking points as bullet points. You do not usually need to include all of them to gain six marks but you do need to write in full sentences, linking them logically and clearly.

Edexcel questions courtesy of Pearson Education Ltd.

Sample question 1 - Foundation


Diesel is the fuel used in most bus engines.

Research is being carried out into the use of hydrogen, instead of diesel, as a fuel for buses.

Discuss the advantages and disadvantages of using hydrogen, rather than diesel, as a fuel for buses.

[6 marks]

Your answer should include the following:

Answers must compare advantages of using hydrogen instead of diesel...

  • plenty of water/raw material
  • limited supplies of crude oil
  • hydrogen produces only water as waste
  • diesel also produces carbon dioxide
  • carbon dioxide emissions may cause global warming
  • diesel undergoes incomplete combustion
  • diesel also produces carbon and/or carbon monoxide
  • carbon is formed as soot and makes objects dirty
  • carbon monoxide is a toxic gas
  • hydrogen can be obtained from the water produced

...with disadvantages of using hydrogen instead of diesel:

  • hydrogen gas has to be manufactured
  • energy/electricity is needed to produce hydrogen
  • producing electricity from non-renewable resources produces carbon dioxide
  • hydrogen is expensive to produce
  • problems of storage of large volumes of flammable gas
  • stronger/heavier/bigger fuel tanks needed
  • hydrogen is a gas and leaks easily if the fuel system is damaged
  • there are limited outlets for buying hydrogen


Sample question 2 - Foundation


When hydrocarbon fuels burn in a plentiful supply of air they undergo complete combustion, forming carbon dioxide and water vapour.

If the air supply is limited incomplete combustion occurs and carbon monoxide and carbon may be formed.

Describe the problems that can be caused by these products of complete and incomplete combustion.

[6 marks]

Your answer should include the following:


  • causes condensation
  • for example, damp walls
  • damages decoration/wallpaper
  • greenhouse gas/keeps in heat

Carbon dioxide:

  • greenhouse gas/keeps in heat
  • contributes to global warming
  • consequences of global warming, eg flooding/drought/crop failure/disease/melting ice caps/climate change


  • soot
  • makes things dirty/black
  • damages decoration/wallpaper
  • flues or jets could be blocked
  • can cause breathing problems
  • can cause fires

Carbon monoxide:

  • toxic
  • odourless and colourless
  • so it is difficult to detect
  • it combines with haemoglobin...
  • red blood cells
  • prevents oxygen being circulated/reduces amount of oxygen in bloodstream


Sample question 3 - Higher


Useful products can be obtained by the fractional distillation of crude oil.

The diagram shows a fractional distillation column and the fractions obtained.

Crude oil and the fractions it releases in distillation.

The petrol fraction is obtained from near the top of the column.

The bitumen fraction is obtained from the bottom of the column.

Explain how the petrol and bitumen fractions differ in their properties and uses. [6 marks]


  • petrol has shorter (carbon) chains
  • petrol has lower melting point/boiling point
  • petrol has lower viscosity
  • petrol ignites/burns more easily
  • bitumen does not combust completely (due to high number of carbon atoms per molecule)
  • burning bitumen produces lots of carbon monoxide/soot

Uses of petrol fraction:

  • fuels in cars/in motorbikes/transport

Uses of bitumen fraction:

  • used for road surfaces
  • used for roofing