This question is about hydrocarbons - AQA - GCSE Chemistry - Question 2 - 2016 - Paper 1
Question 2
This question is about hydrocarbons.
Most of the hydrocarbons in crude oil are alkanes.
Large alkane molecules can be cracked to produce more useful molecules.
Th... show full transcript
Worked Solution & Example Answer:This question is about hydrocarbons - AQA - GCSE Chemistry - Question 2 - 2016 - Paper 1
Step 1
Give two conditions used to crack large alkane molecules.
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Answer
High temperature (around 250-900 °C)
Catalyst such as zeolite or alumina to facilitate the reaction.
Step 2
When alkenes react with bromine water the colour changes from orange to __________.
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colourless.
Step 3
Complete the displayed structure of butane.
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The structure of butane (C₄H₁₀) is shown below:
H H H H
| | | |
H - C - C - C - C - H
| | | |
H H H H
Step 4
Calculate the energy released by 1.0 g of decane in kJ.
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Energy released = 16.80 kJ.
Step 5
Suggest one improvement to the apparatus that would make the temperature increase of the water for each fuel more accurate.
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One improvement could be to use a lid on the beaker to insulate it better and reduce heat loss.
Step 6
A reason why this is an improvement.
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Using a lid helps to ensure that more of the heat generated by the burning fuel goes into the water, thus providing a more accurate reading of the temperature increase.
Step 7
Name this black substance.
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The black substance is carbon soot.
Step 8
Suggest why it is produced.
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It is produced due to incomplete combustion of the fuels, which occurs when there is not enough oxygen available.
Step 9
Give two reasons why the results in Table 1 support this conclusion.
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Hexane has the highest energy released per gram (47 kJ/g), indicating it is more efficient as a fuel.
Hexane produces the least amount of smoke compared to the other fuels, suggesting cleaner combustion.
Step 10
Describe the advantages and disadvantages of using hydrogen instead of petrol in car engines.
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Advantages:
Combustion only produces water, causing no pollutants, thus mitigating environmental impacts.
Hydrogen can be generated from renewable resources, reducing dependency on fossil fuels.
Disadvantages:
Hydrogen has a lower energy density than petrol, requiring larger storage tanks.
Current infrastructure for hydrogen refueling is limited, making it less convenient for widespread use.
