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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 trend is option B: the ease of ignition increases. As we move from top to bottom of the fractional distillation column, the fractions become denser and contain larger molecules, which typically exhibit increased ease of ignition.
Step 2
Explain why alkanes are described as hydrocarbons.
Answer
Alkanes are described as hydrocarbons because they consist solely of hydrogen and carbon atoms. Each alkane molecule contains carbon atoms bonded to hydrogen atoms, and there are no other elements in their structure, making them pure hydrocarbons.
Step 3
Explain the general formula of an alkane?
Answer
The general formula for alkanes is CnH2n+2, where n represents the number of carbon atoms. This means that for every n carbon atoms in an alkane, there are always double the number of hydrogen atoms plus two additional hydrogen atoms. This structure is consistent across all alkanes.
Step 4
Explain the pattern shown by this graph.
Answer
The graph indicates that the boiling points of alkanes increase as the number of carbon atoms increases. This is due to the increase in intermolecular forces, particularly Van der Waals forces, as more carbon atoms lead to larger molecules. Consequently, higher energy is required to break these forces, resulting in higher boiling points.
Step 5
Step 6
Draw the reaction profile of this reaction.
Answer
The reaction profile for the cracking reaction should show:
- A curve starting at a higher energy level for reactants and dropping to a lower energy level for products, indicating that the reaction is endothermic.
- Label the initial position as 'reactants', the final position as 'products', and the peak of the curve as 'activation energy' to demonstrate the energy required to initiate the reaction.
Step 7