Simple and Fractional Distillation (Edexcel GCSE Chemistry): Revision Notes
📚 Revision Notes
Simple and Fractional Distillation
Fractional Distillation and Crude Oil
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Fractional distillation is a process used to separate a mixture into its components based on their different boiling points.
Crude oil is a complex mixture of hydrocarbons extracted from the ground. In its raw state, crude oil isn't very useful because it contains a wide variety of hydrocarbons with different properties. -
- To make crude oil useful, it is separated into simpler mixtures called fractions. Each fraction contains hydrocarbons with similar carbon chain lengths and properties.
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Since the hydrocarbons in crude oil have different boiling points, we can separate them through fractional distillation. By breaking down crude oil into these fractions, we can isolate the hydrocarbons needed for various products, making use of their unique properties.
The Process of Fractional Distillation with Crude Oil
- Heating: Crude oil is heated and enters the fractionating column at the bottom. The column is hottest at the bottom and cools as you move up.
- Condensation: As the vapours rise through the column, hydrocarbons with higher boiling points condense into liquids lower in the column where the temperature is higher.
- Separation: Hydrocarbons with lower boiling points continue to rise higher up the column.
- Fraction Collection: Different hydrocarbons condense at different heights, forming separate fractions. These liquid fractions are then drawn off at various points in the column.
Simple Distillation
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Simple distillation is used to separate a liquid from a solution, where the components have different boiling points. E.g. separating water from seawater, or ink from water.
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Steps:
- Prepare the Equipment:
- Pour the sample (e.g., seawater) into a distillation flask.
- Set Up the Condenser:
- Connect the bottom end of the condenser to a cold tap using rubber tubing to keep the condenser cool.
- Heat the Solution:
- Gradually heat the distillation flask.
- The part of the solution with the lower boiling point will evaporate first (e.g., water from seawater).
- Condensation:
- The evaporated water vapour passes through the condenser, where it cools, condenses, and turns back into liquid.
- The pure liquid is collected in a beaker.
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Key Point: Simple distillation works best when separating liquids with significantly different boiling points.