Organic Chemistry and Crude Oil

IGCSE Edexcel Chemistry
4.1–4.18 Organic Chemistry and Crude Oil
Key Concepts: Hydrocarbons contain only carbon and hydrogen. Homologous series share functional groups and general formulae. Crude oil is separated by fractional distillation; cracking converts long alkanes into shorter alkanes and alkenes.

Section A: Organic Basics

1. Define hydrocarbon, homologous series, functional group and isomerism. [4]
2. Write the general formula for alkanes and alkenes and name the first three of each. [4]

Section B: Representing Organic Molecules

3. Draw displayed formulae for methane, ethane, ethene and ethanol. [4]

Section C: Crude Oil and Combustion

4. Describe fractional distillation of crude oil and name three fractions with uses. [4]
5. State the products of complete and incomplete combustion of hydrocarbons and explain why carbon monoxide is dangerous. [4]

Section D: Pollution and Cracking

6. Explain how NOx and SO₂ are produced and how they contribute to acid rain. [4]
7. Explain cracking and why it is necessary. [3]

Total marks: 27

Mark Scheme

1. Hydrocarbon: C and H only; homologous series: same functional group + general formula; functional group: reactive atom/group; isomerism: same formula, different structure [4]
2. Alkanes: CₙH₂ₙ₊₂ (methane, ethane, propane); alkenes: CₙH₂ₙ (ethene, propene, butene) [4]
3. Correct displayed structures [4]
4. Heat crude oil, vapours rise and condense by boiling point; fractions and uses e.g. gases, gasoline, kerosene, diesel, fuel oil, bitumen (any three) [4]
5. Complete: CO₂ + H₂O; incomplete: CO + C (soot) + H₂O; CO binds haemoglobin reducing oxygen transport [4]
6. NOx from high temperature in engines; SO₂ from sulfur impurities; both form acids with water causing acid rain [4]
7. Cracking breaks long alkanes into shorter alkanes and alkenes; needed to meet demand for fuels and make alkenes [3]