STUDENT SPACE · TOPIC 3

Petroleum and cracking

Connect fraction properties with their uses and explain cracking.

The essentials

Coal, natural gas and petroleum are fossil fuels. Natural gas is mainly methane. Petroleum is a mixture of hydrocarbons.
Moving up: chain length decreases, boiling point decreases, viscosity decreases and volatility increases.
Refinery gas: heating and cooking. Petrol: cars. Naphtha: chemical feedstock. Kerosene: jet fuel.
High temperature and a catalyst break larger alkanes into smaller molecules. Products include alkenes and sometimes hydrogen.

Key vocabulary

English	Chinese
fraction	馏分
volatility	挥发性
cracking	裂化

Quick practice

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

Question 1

Does fractional distillation change the molecules? How does cracking differ?

Need a hint for Question 1?

Separate a physical separation from a chemical reaction.

Check Question 1

Distillation separates molecules. Cracking breaks bonds and makes new molecules.

Question 2

Explain why bitumen collects near the bottom of a fractionating column.

Need a hint for Question 2?

Compare boiling points with the temperature near the bottom.

Check Question 2

Bitumen contains large, long-chain hydrocarbons with very high boiling points. It remains as a heavy residue at the bottom rather than rising through the column as vapour.

Question 3

Complete C₆H₁₄ → C₄H₁₀ + X and name X. State two cracking conditions.

Need a hint for Question 3?

Conserve C and H atoms, then identify the smaller hydrocarbon.

Check Question 3

X = C₂H₄, ethene. High temperature and a catalyst.

Use Lesson 3 in your worksheet for written practice. Your teacher will discuss those answers in class.

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