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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?
Answer
The correct answer is B: the ease of ignition increases. As you move down the fractional distillation column, the fractions consist of larger and more complex molecules, which generally have higher boiling points and lower ease of ignition.
Step 2
Step 3
Explain why alkanes are described as hydrocarbons.
Answer
Alkanes are described as hydrocarbons because they are organic compounds made solely of hydrogen and carbon atoms. The term 'hydrocarbon' reflects the specific chemical composition of these molecules, consisting of carbon atoms bonded to hydrogen atoms.
Step 4
Explain the pattern shown by this graph.
Answer
The graph shows that as the number of carbon atoms in the alkane increases, the boiling point also increases. This trend is due to the greater molecular size leading to stronger intermolecular forces, such as van der Waals forces, which require more energy to overcome as the number of carbon atoms increases.
Step 5
Use the information in Figure 5 to give the name of the fraction that is most likely to need to be cracked.
Answer
The fraction that is most likely to need to be cracked is fuel oil. Figure 5 indicates a low relative amount for fuel oil compared to a higher demand, suggesting that cracking may be required to meet this demand.
Step 6
On the axes provided, 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.
Answer
In the reaction profile diagram, the y-axis shows heat energy while the x-axis represents progress of reaction. The reactants should be labeled at a higher energy level, followed by a peak for activation energy, and then a lower energy level for the products, indicating that the reaction is endothermic.
Step 7