Separating Mixtures (Filtration, Crystallisation, Distillation)

Filtration

Filtration is a method used to separate an insoluble solid from a liquid. It works because the solid particles are too large to pass through the tiny pores in the filter paper, while the liquid passes through easily.

The apparatus needed includes a funnel and filter paper. The mixture is poured into the funnel lined with filter paper. The liquid that passes through is called the filtrate, and the solid left on the paper is called the residue.

Filtration is commonly used in everyday life, for example:

• Separating tea leaves from brewed tea
• Filtering muddy water to remove solid dirt particles

It is important to note that filtration only works if the solid is insoluble in the liquid. If the solid dissolves, filtration will not separate it.

For instance, if you have a mixture of sand and water, filtration can separate the sand (solid residue) from the water (liquid filtrate).

Crystallisation

Crystallisation is used to separate a soluble solid from a solution. It involves evaporating the solvent (usually water) to concentrate the solution until crystals start to form, then allowing the solution to cool so crystals grow.

The process steps are:

• Heat the solution gently to evaporate some solvent
• Stop heating when crystals begin to form (saturated solution)
• Allow the solution to cool slowly so crystals grow larger
• Filter to collect the crystals and dry them

Crystallisation is commonly used to purify salts from solutions, for example, obtaining pure copper sulfate crystals from copper sulfate solution.

For example, if you have salt dissolved in water, you can evaporate the water to get salt crystals.

Simple Distillation

Simple distillation is used to separate a liquid from a solution, especially when the liquid has a much lower boiling point than the dissolved solid or other liquids.

The process involves:

• Heating the solution to evaporate the liquid
• Vapour rises and passes into a condenser
• In the condenser, the vapour cools and condenses back into a liquid
• The purified liquid (distillate) is collected separately

Simple distillation is used to obtain pure water from saltwater or to separate a solvent from a solution.

For example, to get pure water from seawater, heat the seawater until water evaporates, then cool and collect the water vapour as pure water.