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Crude oil is a complex mixture of substances - Edexcel - GCSE Chemistry - Question 6 - 2018 - Paper 1
Question 6
Crude oil is a complex mixture of substances. (a) Crude oil can be separated into useful fractions by fractional distillation. Figure 7 shows a fractional distilla... show full transcript
Worked Solution & Example Answer:Crude oil is a complex mixture of substances - Edexcel - GCSE Chemistry - Question 6 - 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 property of boiling points is a significant trend observed in the fractions obtained from the top to those at the bottom of the fractional distillation column. As we move down the column, the boiling points of the fractions generally increase. This occurs because smaller molecules with fewer carbon atoms, found at the top, have weaker intermolecular forces, resulting in lower boiling points. Conversely, larger molecules at the bottom have stronger Van der Waals forces due to higher molecular weight, leading to higher boiling points.
Step 2
Step 3
Explain why alkanes are described as hydrocarbons.
Answer
Alkanes are described as hydrocarbons because they are composed solely of carbon (C) and hydrogen (H) atoms. These compounds contain only carbon-hydrogen bonds along with carbon-carbon bonds, making them part of the hydrocarbon family. This classification is significant because hydrocarbons are the fundamental building blocks for various organic compounds and fossil fuels.
Step 4
Explain the pattern shown by this graph.
Answer
The graph illustrates a positive correlation between the number of carbon atoms in alkanes and their boiling points. As the number of carbon atoms increases, the boiling points tend to rise. This trend can be attributed to the increasing size of the alkane molecules, which enhances the strength of intermolecular forces, particularly Van der Waals forces, requiring more energy (in the form of heat) to break these interactions and convert the liquid to gas.
Step 5
Use the information in Figure 9 to give the name of the fraction that is most likely to need to be cracked.
Answer
The fraction most likely to be cracked is 'fuel oil'. This is indicated by the discrepancy between the relatively low amount obtained from distillation compared to its higher demand.
Step 6
Draw the reaction profile of this reaction.
Answer
To illustrate the reaction profile for an endothermic cracking reaction,
- Begin with a horizontal line representing the energy level of the reactants on the left side of the graph.
- Create a curve that rises to a peak; this peak represents the activation energy of the reaction.
- After reaching the peak, draw a line that descends to a lower level representing the energy of the products, which should be lower than the activation energy peak but still above the reactants' level (indicating the net gain of energy).
- Label the reactants, products, and activation energy clearly on the graph.
Step 7