Year 9 Science · Unit 2 · Lesson 13
Apply Worksheet
Learning Goals
1. Give the IUPAC prefix for a chain of 4, 7 and 8 carbon atoms, and state what the ending -ane tells you about the molecule.
Complete the table
Each row is one straight-chain alkane. Fill in the empty cells.
| Name | Molecular formula | Condensed formula |
|---|---|---|
| heptane | ||
| C₂H₆ | ||
| CH₃CH₂CH₂CH₂CH₂CH₃ | ||
| octane |
Scenario
A student is handed a card showing CH₃–CH₂–CH₂–CH₃. She must name it, then predict how its boiling point compares with propane’s −42 °C.
2. (a) Count the carbon atoms in CH₃–CH₂–CH₂–CH₃ and write its IUPAC name. (b) Predict whether it boils above or below −42 °C, and justify your prediction using chain length.
3. C₄H₁₀ has two structural isomers. Draw the displayed formula of each: butane (a straight chain) and 2-methylpropane (a chain of three carbons with the fourth carbon joined to the middle one).
Read the data
| Molecular formula | Shape of isomer | Boiling point (°C) |
|---|---|---|
| C₄H₁₀ | straight chain | −1 |
| C₄H₁₀ | branched | −12 |
| C₅H₁₂ | straight chain | 36 |
| C₅H₁₂ | most branched | 10 |
| C₆H₁₄ | straight chain | 69 |
| C₆H₁₄ | most branched | 50 |
Source: measured values, rounded.
4. For each molecular formula, calculate how many degrees lower the branched isomer boils than the straight-chain isomer.
C₄H₁₀ C₅H₁₂ C₆H₁₄ °C
5. Describe the pattern in Table 1 for isomers with the same formula. Explain it using how closely the molecules can pack together.
6. Straight-chain octane boils at 126 °C. Isooctane is a branched isomer of octane. Predict whether isooctane boils above or below 126 °C, and justify your prediction from Table 1.
7. A can of lighter gas is labelled only “C₄H₁₀”. Explain why this label does not tell you exactly which substance is in the can, and suggest a better label.