Six-mark questions
Six-mark questions are extended open response questions. These require longer answers than the structured questions with fewer marks. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.
Six-mark questions are marked using a levels-based mark scheme because they are open ended. To gain full marks, you need to:
- support explanations using scientific knowledge and understanding
- use appropriate scientific words and terms
- write clearly, linking ideas in a logical way
- maintain a sustained line of reasoning, rather than getting lost or bogged down
You are likely to see command words such as:
- 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. This means they 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.
Remember that the topics covered in the first paper are assumed knowledge for the second paper, so questions in the second paper may need knowledge and understanding of those topics too.
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.
Sample question 1 - Foundation
Question
Fractional distillation separates crude oil into useful fractions.
Look at the table. It shows some information about fractions obtained from crude oil.
| Fraction | Boiling temperature in 掳C |
| bitumen | above 350 |
| LPG | less than 40 |
| fuel oil | 300 to 350 |
| heating oil | 250 to 300 |
| petrol | 40 to 200 |
| paraffin | 200 to 250 |
| Fraction | bitumen |
|---|---|
| Boiling temperature in 掳C | above 350 |
| Fraction | LPG |
|---|---|
| Boiling temperature in 掳C | less than 40 |
| Fraction | fuel oil |
|---|---|
| Boiling temperature in 掳C | 300 to 350 |
| Fraction | heating oil |
|---|---|
| Boiling temperature in 掳C | 250 to 300 |
| Fraction | petrol |
|---|---|
| Boiling temperature in 掳C | 40 to 200 |
| Fraction | paraffin |
|---|---|
| Boiling temperature in 掳C | 200 to 250 |
List the fractions in the position, from top to bottom, that they 鈥榚xit鈥 the fractionating column. Explain how fractional distillation separates crude oil into fractions. [6 marks]
OCR Gateway Science, GCE Chemistry, Paper B741, May 2013.
The following are vaild points that could be included in your answer. It is important that you do not bullet point your answer but write your sentences in full.
Order of fractions:
- LPG, petrol, paraffin, heating oil, fuel oil, bitumen
Fractional distillation:
- crude is heated
- vapours enter the bottom of the column
- column has a temperature gradient
- column is hot at the bottom and cold at the top
- vapours rise
- vapours cool as they rise
- vapours condense when they reach their boiling temperature
- liquids fed out of the column
- LPG/gases exit from the top
- bitumen exits from the bottom
- fractions contain mixtures of hydrocarbons
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Sample question 2 - Foundation
Question
Describe how propene reacts to form a polymer.
In your answer, give the name of the polymer, the type of polymerisation and what happens to the propene molecules. [6 marks]
OCR Gateway Science, GCE Chemistry, Paper B741, January 2012.
The following are vaild points that could be included in your answer. It is important that you do not bullet point your answer but write your sentences in full.
Polymer:
- poly(propene)/polypropene/polypropylene
Polymerisation:
- addition polymerisation
Description of polymerisation:
- many (small) molecules join together
- to make a large molecule or polymer
- small molecules or propene (molecules) are called the monomer
- monomers are alkenes
- double bond in monomer breaks and molecules join together
- unsaturated monomer molecules join to give saturated polymer molecule
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Sample question 3 - Higher
Question
Most cars have engines fuelled by diesel or petrol.
Hydrogen-oxygen fuel cells have been developed for cars.
Describe the advantages and disadvantages of hydrogen-oxygen fuel cells for cars. In your answer, include the reactions that take place in these cells, and the nature of any products formed by a car in use. [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.
The following are vaild points that could be included in your answer. It is important that you do not bullet point your answer but write your sentences in full.
Reactions:
- hydrogen molecules lose electrons to form hydrogen ions and electrons
- H2 鈫 2H+ + 2e-
- electrons travel through electrical circuit
- hydrogen ions pass through membrane to the other side of the cell
- hydrogen ions react with oxygen and electrons to form water
- 4H+ + O2 + 4e- 鈫 2H2O
- overall reaction is 2H2 + O2 鈫 2H2O
Products:
- fuel cells: water only
- diesel or petrol cars: carbon dioxide and water
- diesel or petrol cars: carbon monoxide/sulfur dioxide/oxides of nitrogen
Advantages of fuel cells:
- fewer moving parts
- quiet in use, so less noise pollution
- only product is water
- many ways to make hydrogen
Disadvantages of fuel cells:
- very few filling stations
- hydrogen is more difficult to store than petrol or diesel
- quiet in use, so pedestrians may not hear the car coming
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