The diagram shows the structure of a propene molecule - Edexcel - GCSE Chemistry - Question 3 - 2011 - Paper 1
Question 3
The diagram shows the structure of a propene molecule.
(a) Which row of the table describes propene?
Put a cross (✓) in the box next to your answer.
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Worked Solution & Example Answer:The diagram shows the structure of a propene molecule - Edexcel - GCSE Chemistry - Question 3 - 2011 - Paper 1
Step 1
Which row of the table describes propene?
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Answer
Propene is a hydrocarbon and it is unsaturated. Therefore, the correct answer is C: yes for hydrocarbon and yes for unsaturated.
Step 2
Draw a diagram to show the part of a poly(propene) molecule formed from two propene molecules.
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Answer
A diagram should illustrate two propene molecules linking together through their double bonds, resulting in a long chain. Each double bond converts to a single bond to form the polymer.
Step 3
Describe a test that shows that molecules of propene contain carbon to carbon double bonds.
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Answer
One common test is to react propene with bromine water. The decolorization of bromine water indicates the presence of a double bond, as the bromine adds across the double bond, forming a dibrominated alkane.
Step 4
Give the total mass of products formed if 17 g of decane is cracked in this way.
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Answer
Assuming the reaction is balanced, if 17 g of decane (C₁₀H₂₃) is cracked, the total mass of products will equal the mass of reactants. Therefore, the total mass of propene and butane formed is also 17 g.
Step 5
Explain what is meant by cracking.
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Answer
Cracking is a process used in the petroleum industry to break down large hydrocarbon molecules into smaller, more useful molecules, such as alkenes and shorter-chain alkanes.
Step 6
Explain why it is necessary to crack crude oil fractions that contain large molecules.
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Answer
Cracking is necessary because large molecules from crude oil are less useful; for instance, they can’t be used as fuels directly. By cracking, we produce smaller alkanes and alkenes which have specific uses, such as fuel for cars or as monomers to make plastics.
