Year 9 Science · Unit 2 · Lesson 12
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Learning Goals
1. Classify crude oil as an element, a compound or a mixture. Justify your answer using what it is made of.
Order the steps
These stages of fractional distillation are jumbled. Number them 1 to 5 in the correct order.
| Order | Stage |
|---|---|
| Each fraction condenses to a liquid where the temperature drops below its boiling point. | |
| Crude oil is heated to about 400 °C in a furnace, and most of it turns to vapour. | |
| The liquid fraction is piped out of the column at that height. | |
| The vapour enters the bottom of the fractionating column. | |
| The vapour rises and cools as it moves up the column. |
2. A student says: “Bigger molecules rise further up the column before they condense.” Is this correct? Use boiling point in your answer.
Real-world context: Australia’s refineries
In 2021, two of Australia’s four oil refineries closed: Altona in Victoria and Kwinana in Western Australia. Only Viva Energy’s Geelong refinery and Ampol’s Lytton refinery in Brisbane still turn crude oil into fuels. Australia still pumps some crude oil, but most of its petrol, diesel and jet fuel now arrives by ship, already refined overseas.
3. Explain why a country that has its own crude oil but no refinery still cannot run its cars and trucks on that oil.
Teacher demonstration: distilling crude oil in a boiling tube
In a fume cupboard, a teacher heated 20.0 mL of a synthetic crude oil in a boiling tube fitted with a thermometer. As the temperature rose, she collected four fractions in separate test tubes. The class recorded each fraction.
| Fraction | Temperature range (°C) | Volume (mL) | Appearance and flow |
|---|---|---|---|
| 1 | 20–80 | 4.2 | colourless, very runny |
| 2 | 80–150 | 5.6 | pale yellow, runny |
| 3 | 150–230 | 4.8 | yellow, flows slowly |
| 4 | 230–300 | 3.0 | orange-brown, thick |
| Left in tube | above 300 | 2.4 | dark brown, sticky |
Source: sample class results.
4. Show that the volumes in Table 1 add up to the 20.0 mL that was heated. Then calculate the percentage of the crude oil that was collected as fraction 2.
Fraction 2 %
5. Describe the pattern in the appearance and flow of the fractions. Explain the pattern using chain length.
6. A boiling tube has no tall column, so each fraction is less cleanly separated than at a refinery. Use Table 1 to explain why each test tube still holds a mixture, not one compound.
7. LPG (1–4 carbon atoms per molecule) fuels barbecues and caravan cooktops. Diesel (14–20 carbon atoms, boiling range 250–350 °C) fuels trucks, trains and ships. Diesel only catches fire above about 55 °C. Explain why each fraction suits its use, using chain length and boiling point.