Year 9 Science · Unit 2 · Lesson 13

Naming and Representing Alkanes

Challenge Worksheet

Name

Date

Class

Learning Goals

Explain the logic of the IUPAC prefix system clearly enough that another student can apply it correctly.
Predict physical properties of alkanes (state, boiling point, crude oil fraction) from their name and formula.
Justify predictions using chain length, intermolecular forces, and crude oil distillation knowledge.

Go Deeper

Explain it to a student who keeps getting confused

A classmate keeps mixing up IUPAC prefixes and can't figure out why "oct-" means 8. Use the sentence starters below to explain the system clearly. You can use memory tricks, patterns, or real examples.

"The prefix tells you the number of carbon atoms, the system works like…"

"So if you see 'hex' at the start of an alkane name, you know…"

"The '-ane' ending is important because it tells you…"

"The tricky part is that prefixes like meth-, eth-, prop-, but- don't follow an obvious pattern, here's a memory trick…"

Show What You Know

1. A chemist labels a gas cylinder "octane C₈H₁₈". Without measuring, predict its state at room temperature and its approximate boiling point range. Then predict which crude oil fraction it would be collected in. Justify all three predictions using chain length and intermolecular force reasoning.

Challenge 4 marks

2. Two students disagree about why chemists use condensed structural formulas instead of always writing molecular formulas. Student A says: "A molecular formula like C₆H₁₄ is enough, it tells you everything." Student B says: "No, the condensed formula CH₃(CH₂)₄CH₃ gives you more useful information." Evaluate both positions. Who is correct, and why? Use hexane as your example.

Challenge 3 marks

Wrap Up

In one sentence, what was the main idea of this lesson?