Crude oil is a complex mixture of substances - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2018 - Paper 1
Question 4
Crude oil is a complex mixture of substances.
(a) Crude oil can be separated into useful fractions by fractional distillation.
Figure 3 shows a fractional distilla... show full transcript
Worked Solution & Example Answer:Crude oil is a complex mixture of substances - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2018 - Paper 1
Step 1
Which of the following is a trend in a property of the fractions obtained from the top to those obtained from the bottom?
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Answer
The answer is B) the ease of ignition increases. As we move down the fractional distillation column, the fractions become heavier and thus are less volatile and easier to ignite.
Step 2
Explain why alkanes are described as hydrocarbons.
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Answer
Alkanes are described as hydrocarbons because they are organic compounds consisting only of hydrogen and carbon atoms. This means that their molecular structure is based solely on these two elements.
Step 3
Explain the pattern shown by this graph.
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Answer
The graph indicates that as the number of carbon atoms in the alkane increases, the boiling point also increases. This can be attributed to the increase in Van der Waals forces or London dispersion forces between the molecules, which require more energy to break as the size of the molecules increases.
Step 4
Use the information in Figure 5 to give the name of the fraction that is most likely to need to be cracked.
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Answer
The fraction that is most likely to need to be cracked is fuel oil, as indicated by its relatively high demand in comparison to its production.
Step 5
Draw the reaction profile of this reaction. Label the energy of the reactants, the energy of the products and the activation energy of the reaction.
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Answer
In drawing the reaction profile, start with a vertical axis for heat energy and a horizontal axis for the progress of the reaction. The energy of the reactants will be lower than the peak of the activation energy. The energy of the products will be lower than the reactants, indicating that the reaction is endothermic.
Step 6
Complete the equation for the cracking of dodecane by filling in the formula of the single molecule needed to balance the equation.
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Answer
C₁₂H₂₆ → C₈H₁₈ + C₄H₈. Here, dodecane decomposes into octane and butene.
