April 23, 2019
For IGCSE Chemistry, you need to know various techniques to separate mixtures.
Filtration
Filtration is used to separate insoluble solid from a mixture of the solid and liquid.
- A filter paper is placed on a filter funnel on a beaker.
- The mixture of insoluble solid and liquid is poured onto the filter funnel.
- The small pores on the filter paper allow liquid particles to pass through.
- Large solid particles cannot pass through the filter paper and are left as a residue.
Example: separate sand from a mixture of water and sand
Crystallization
Crystallization is used to separate soluble solid from a solution.
- When the solution is heated, the solvent evaporates, leaving a saturated solution.
- Allow the saturated solution to cool down, then solids come out of the solution and crystals grow.
- The crystal is collected by filtration and dried.
Example: separate copper (II) sulfate from copper (II) sulfate solution
Simple Distillation
Simple distillation is used to separate solvent from a solution.
- The solute has a much higher boiling point compared to the solvent.
- When the solution is heated, solvent vapor rises and evaporates.
- As the solvent vapor passes through the condenser, it cools down and condenses into liquid.
- When all the solvent has evaporated, only the solute is left in the distillation flask.
Example: separate pure water from sea water
Fractional Distillation
Fractional distillation is used to separate liquids from a mixture of liquids with different boiling points.
- When the mixture is heated, vapors rise through a fractionating column that is hotter at the bottom and cooler at the top.
- Vapors of different liquids condense when they reach the part of the column that is below their boiling point.
- Different liquid can be obtained at different parts of the column, or by continuing to heat the mixture to increase the temperature in the column.
Example: separate fractions from crude oil, or separate ethanol from mixture of ethanol and water
Paper Chromatography
Paper chromatography is used to separate mixture of soluble substances in a solvent.
- Spots of the mixture/dye are placed on the base line, and the chromatography paper is lowered until the base line barely touches the solvent.
- As the solvent travels up the paper, it takes the soluble substances with it.
- Since different substances have different solubilities in the solvent, it will travel at different rates.
- This will show the different components of the mixture.
Example: chlorophyll from plant leaf extracts
For a more detailed explanation of paper chromatography, click here.
Paper chromatography is used to separate mixture of soluble substances in a solvent.
- Spots of the mixture/dye are placed on the base line, and the chromatography paper is lowered until the base line barely touches the solvent.
- As the solvent travels up the paper, it takes the soluble substances with it.
- Since different substances have different solubilities in the solvent, it will travel at different rates.
- This will show the different components of the mixture.
Example: chlorophyll from plant leaf extracts