Quick Overview
- Fossil Fuels & Fractional Distillation: Crude oil contains a mixture of hydrocarbons separated by boiling point into useful fractions
- Alkanes: Saturated hydrocarbons (CnH2n+2) with only single C-C bonds; unreactive but undergo combustion and substitution
- Alkenes: Unsaturated hydrocarbons (CnH2n) with C=C double bonds; more reactive and undergo addition reactions
- Cracking: Breaking large alkanes into smaller, more useful products by heating with a catalyst
- Alcohols: Compounds with -OH functional group; can be made by hydration of alkenes or fermentation of glucose
- Carboxylic Acids: Weak acids containing -COOH group; react with bases and metals to form salts
- Esters: Formed from alcohol + carboxylic acid; sweet-smelling liquids used in flavorings and perfumes
🛢️ Fossil Fuels & Fractional Distillation
Hydrocarbons are compounds made from hydrogen and carbon atoms only. The most common fossil fuels are coal, natural gas (mainly methane, CH₄), and petroleum (crude oil).
Crude oil is a thick, black liquid found under porous rock beneath the ground and sea. It's a mixture of hydrocarbons at different sizes—some useful, some not. We need to separate these into fractions.
Fractional distillation works because molecules of different chain lengths have different boiling points. Longer chains attract each other more strongly (via van der Waals forces), so they need more heat to vaporize and condense at the bottom of the hot column. Shorter chains vaporize easily and rise to the cooler top.
Process:
• Crude oil is heated to ~350°C and vaporized
• Vapors enter a fractionating column (hot at bottom, cool at top)
• High boiling point molecules → condense at bottom
• Low boiling point molecules → rise and condense at top
• Different fractions are collected at different heights
Properties Down the Column
| Property |
Trend Down Column |
Why? |
| Boiling Point |
Increases |
Larger molecules have stronger intermolecular forces |
| Viscosity |
Increases (thicker) |
More atoms = stronger attraction between molecules |
| Volatility |
Decreases |
Harder to vaporize as size increases |
| Chain Length |
Increases |
More carbon atoms per molecule |
Fractions & Their Uses
| Fraction |
C Atoms |
Boiling Point |
Use |
| Refinery Gas |
1–4 |
<25°C |
Heating and cooking fuel |
| Gasoline |
4–12 |
40–100°C |
Car fuel (petrol) |
| Naphtha |
7–14 |
90–150°C |
Raw material for chemicals |
| Kerosene |
12–16 |
150–240°C |
Jet fuel (paraffin) |
| Diesel |
14–18 |
220–300°C |
Diesel engine fuel |
| Fuel Oil |
19–25 |
250–320°C |
Ship and home heating fuel |
| Bitumen |
>70 |
>350°C |
Road surfacing |
💡 Remember:
Practice: Why does the boiling point of fractions increase going down the fractional distillation column?
⛓️ Alkanes
Alkanes
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