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.
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
Ammonium nitrate is a salt used as a fertiliser.
A student is told to use four stages to prepare pure, dry crystals of ammonium nitrate:
- take 25.0 cm3 of ammonia solution
- find the volume of nitric acid that is needed to neutralise the ammonia solution
- use this result to prepare an ammonium nitrate solution
- prepare pure, dry crystals of ammonium nitrate from this solution
Some of the following apparatus may be used in the experiment.
Describe how the student should carry out this experiment.
[6 marks]
Edexcel question courtesy of Pearson Education Ltd.
Your answer should include the following:
Stage 1:
- identifies pipette
- pipette/measuring cylinder to measure out the ammonia solution (25 cm3)
- into a suitable container, eg conical flask
Stage 2:
- add few drops of indicator/suitable named indicator
- put flask on a white tile
- identifies burette
- fill burette with nitric acid solution
- clamp burette/burette holder/stand
- read level of burette
- add acid from the burette
- swirl flask (gently)
- add drop-wise near end-point
- until indicator just changes colour/correct colour change for chosen indicator
- read level on burette
- repeat experiment until concordant results
Stage 3:
- mix the same volumes of nitric acid and ammonia solution (determined from the titration experiment)
- but leaving out the indicator
Stage 4:
- pour into an evaporating dish
- heat the solution/leave to evaporate to dryness, until pure salt crystals formed
- to point of crystallisation/concentrate solution
- leave to cool
- filter off crystals
- wash with water
- leave to dry
Sample question 2 - Higher
Question
Ammonium sulfate is a salt used as a fertiliser. It can be prepared in the laboratory, and in fertiliser factories.
Compare and contrast these two ways to prepare ammonium sulfate.
[6 marks]
This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.
Your answer should include the following:
Similarities:
- both use ammonia/ammonia solution
- both use sulfuric acid
- both produce ammonium sulfate
Differences:
| Feature | Laboratory preparation | Factory preparation |
| Scale | Small | Large |
| Number of stages | Small number | Several/more |
| Starting materials | Ammonia solution and sulfuric acid | Raw materials for making ammonia solution and sulfuric acid/named raw material, eg air, water, natural gas, sulfur |
| Type of process | Batch | Continuous |
| Feature | Scale |
|---|---|
| Laboratory preparation | Small |
| Factory preparation | Large |
| Feature | Number of stages |
|---|---|
| Laboratory preparation | Small number |
| Factory preparation | Several/more |
| Feature | Starting materials |
|---|---|
| Laboratory preparation | Ammonia solution and sulfuric acid |
| Factory preparation | Raw materials for making ammonia solution and sulfuric acid/named raw material, eg air, water, natural gas, sulfur |
| Feature | Type of process |
|---|---|
| Laboratory preparation | Batch |
| Factory preparation | Continuous |
Sample question 3 - Higher
Question
The reaction between nitrogen and hydrogen is exothermic.
N2(g) + 3H2(g) ⇌ 2NH3(g)
One factory uses this set of conditions:
If nitrogen and hydrogen were reacted at 150 atm pressure and 300°C, without a catalyst, some ammonia would be formed.
Another factory uses this set of conditions:
In the Haber process a pressure of 150 atm and a temperature of 450°C are used, in the presence of an iron catalyst.
Explain why the conditions used in the second factory will generate more profit using ideas about yield and rate.
[6 marks]
Edexcel question courtesy of Pearson Education Ltd.
Your answer should include the following:
- higher temperature reaches equilibrium faster because molecules move faster
- therefore there are more frequent collisions because molecules have more energy
- therefore more collisions have required energy but yield will be lower
- this is because higher temperature favours endothermic reaction and so equilibrium shifts to left-hand side
- which is because of decomposition of ammonia/ammonia reforms elements
- catalyst causes reaction to reach equilibrium faster/catalyse
- this increases rates (of both forward and back reactions)
- this lowers the activation energy (of both forward and back reactions) but does not affect yield
- equilibrium position not affected
Sample question 4 - Higher
Question
Pure metal can be converted into alloys.
In many cases alloys are more useful than pure metals, for example they are stronger. Gold alloys, stainless steel and magnalium are examples of useful alloys.
Describe how alloying improves the usefulness of metals and how strength is increased, using ideas about the structure of the alloy.
You may use diagrams to help your answer.
[6 marks]
Edexcel question courtesy of Pearson Education Ltd.
Your answer should include the following:
Property change (other than increased strength) or use of alloy:
- increased hardness
- decreased malleability
- increased corrosion resistance
- gold alloy for jewellery
- stainless steel used for cutlery
- steel used for construction
- magnalium used for aircraft
- idea of any use of metal after alloying
Iron:
- iron is a more reactive metal than gold and less reactive than aluminium/middle of reactivity series
- found combined with other elements
- it is extracted by heating with carbon
- carbon is more reactive than iron
- electrolysis can be used
- but electrolysis is more expensive (than heating with carbon)
Structural change:
- pure metal - atoms are all the same size/suitable diagram of pure metal structure
- atoms arranged in a regular way/lattice
- alloy - atoms are of different sizes/suitable diagram of alloy structure
- disrupts arrangement of atoms
- atoms in pure metal structure can slide over each (when bent)
- alloy - sliding prevented by different sized atoms
