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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, which states that the 'ease of ignition increases.' As we move down the fractional distillation column, the fractions become heavier and have larger molecular structures, which typically leads to a greater ease of ignition due to the increased carbon chain length.
Step 2
Explain why alkanes are described as hydrocarbons.
Answer
Alkanes are described as hydrocarbons because they are organic compounds comprised exclusively of hydrogen and carbon atoms. Their general formula is CnH2n+2, which indicates that for every carbon atom in the molecule, there are two additional hydrogen atoms. This composition classifies them as hydrocarbons.
Step 3
Explain the pattern shown by this graph.
Answer
The graph illustrates that as the number of carbon atoms in an alkane increases, the boiling point also increases. This is primarily due to the stronger van der Waals forces and London dispersion forces that arise from the greater surface area of larger alkane molecules, making it more difficult for the molecules to escape into the gas phase.
Step 4
Step 5
Draw the reaction profile of this reaction.
Answer
The reaction profile for the cracking of dodecane should show a diagram where the reactants are at a higher energy level than the products. Label the 'reactants' and 'products' along with the 'activation energy', which represents the energy barrier that must be overcome for the reaction to proceed. Ensure that the 'heat energy' axis is vertical and 'progress of reaction' is horizontal.
Step 6