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.
Writing six-mark answers with Dr Alex Lathbridge
Listen to the full series on BBC Sounds.
How to write six-mark answers in your science GCSE exams.
Sample question 1 - Foundation
Question
A technician found some colourless crystals in an unlabelled beaker in a laboratory.
The technician knew that the substance was either potassium chloride, potassium carbonate, sodium chloride or sodium iodide.
Plan a series of tests the technician could carry out to identify the colourless crystals.
[6 marks]
Answers must give a logical description of how tests can be used to identify all four substances.
Your answer should include the following:
- flame test
- description of carrying out a flame test
- if the flame is yellow/not lilac, sodium ions present
- if the flame is lilac/not yellow, potassium ions present
- add dilute {hydrochloric/nitric} acid to the solid
- if bubbles of gas form then carbonate ions present
- bubble gas through limewater
- if limewater turns milky/cloudy, carbon dioxide present
- make a solution of the crystals in water
- add dilute nitric acid
- if no reaction with acid, add silver nitrate solution
- if there is a white precipitate, chloride ions present
- if there is a yellow precipitate, iodide ions present
Sample question 2 - Foundation
Question
Many plastic bags are used by shoppers and then thrown away.
Most of these plastic bags are sent to landfill sites.
Two ways of reducing the amount of plastic in landfill sites are to recycle the plastic or to burn it.
Describe the possible environmental advantages and disadvantages of recycling and of burning plastics.
[6 marks]
Your answer should include the following:
Recycling – advantages:
- saves raw materials/saves crude oil/saves making more plastic
- landfill sites do not fill up...
- ...as plastics are non-biodegradable
- less possible damage to animals from discarded waste
- less energy used in recycling than in starting from crude oil
Recycling – disadvantages:
- transport to collection area/recycling point uses fuel
- collection point may cause litter problem/eyesore
- plastics need to be sorted
Burning – advantages and disadvantages:
- volume/amount of waste (bags) decreased
- energy released can be used
- landfill sites do not fill up...
- ...as plastics are non-biodegradable
- burning could produce toxic/poisonous fumes/harmful gases
- burning produces carbon dioxide
Sample question 3 - Higher
Question
Polymers are addition or condensation polymers.
Polymers can be formed by using the monomers shown in the table.
Explain, using appropriate monomers from the table, how different polymers can be formed.
[6 marks]
Polymers:
- polymer molecules are long chains
- made up of simple repeating units
Addition polymer:
- use chloroethene (only)
- to form poly(chloroethene)
- which is addition polymerisation
- one of the bonds in the double bond in chloroethene molecule breaks
- and chloroethene molecules join together to form a long chain molecule
- equation, for example:
Condensation polymer:
- use ethane-1,2-diol and ethanedioic acid
- to form a polyester
- which is condensation polymerisation
- identification of repeat unit
- alcohol group combines with a carboxylic acid group
- and an ester link formed
- with a water molecule eliminated
Sample question 4 - Higher
Question
A technician found some colourless crystals of a substance left, unlabelled, in a beaker in a laboratory.
She knew the substance was one of potassium sulfate, potassium iodide, sodium sulfate or sodium iodide.
Explain how, using chemical tests, the technician could find out if the substance left in the beaker was potassium sulfate, potassium iodide, sodium sulfate or sodium iodide.
You may include equations in your answer.
[6 marks]
Your answer should include the following:
Test for cation:
- flame test
- if the flame is yellow/not lilac, sodium ions are present
- if the flame is lilac/not yellow, potassium ions are present
Test for iodide ions:
- make a solution of the crystals in water
- add dilute nitric acid
- add silver nitrate solution
- if there is a yellow precipitate, iodide ions are present
- if there is no precipitate, sulfate ions are present
- Ag+ + I- → AgI
Test for sulfate ions:
- make a solution of the crystals in water
- add dilute hydrochloric/nitric acid
- add barium chloride/nitrate solution
- if there is a white precipitate, sulfate ions are present
- if there is no precipitate, iodide ions are present
- Ba2+ + SO42- → BaSO4
