Fractional distillation of petroleum
Petroleum is heated so that hydrocarbons vaporise. The vapours enter a fractionating column. The column is hot at the bottom and cooler at the top. Hydrocarbons condense at different heights because they have different boiling points.
COOLER TOP
┌─────────────────────────────┐
│ refinery gas │ shortest chains, lowest b.p., highest volatility
│ gasoline / petrol │
│ naphtha │
│ kerosene / paraffin │
│ diesel / gas oil │
│ fuel oil │
│ lubricating oil │
│ bitumen │ longest chains, highest b.p., lowest volatility
└─────────────────────────────┘
HOTTER BOTTOM
Moving up the column Chain length decreases, boiling point decreases, viscosity decreases, and volatility increases.
Moving down the column Chain length increases, boiling point increases, viscosity increases, and volatility decreases.
Short-answer assessment: 30 marks
Answer all questions. These responses will be submitted to the backend for manual marking.
[2] Q1. Name the three fossil fuels listed in this syllabus section.
[2] Q2. State the main constituent of natural gas and give its chemical formula.
[2] Q3. Define the term hydrocarbon .
[2] Q4. Explain why petroleum is described as a mixture of hydrocarbons.
[4] Q5. Describe how petroleum is separated into useful fractions by fractional distillation.
[4] Q6. Describe how chain length, volatility, boiling point, and viscosity change from the bottom to the top of the fractionating column.
[3] Q7. Give the use of refinery gas, gasoline/petrol, and naphtha.
[3] Q8. Give the use of kerosene/paraffin, diesel oil/gas oil, and fuel oil.
[2] Q9. Give the use of lubricating oil and bitumen.
[3] Q10. Explain why refinery gas is collected near the top of the column, while bitumen remains near the bottom.
[3] Q11. A student says, “fractions at the top of the column have longer chains and higher boiling points.” Explain and correct the mistake.
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Total marks: 30 | Status sent to backend: Manual marking required
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