Separating Earth’s Mixtures

Students explore different methods to separate mixtures.


In this lesson we will be exploring how to separate mixtures created by the Earth. Previous information from lessons 1 and 2 will be incorporated into this lesson to help push and connect your understanding. In many cases when separating mixtures we take advantage of the different properties of the elements, for example, in a salt-water solution we can evaporate the water to extract the salt because the boiling point of water is far lower than the boiling point of salt.

Desalinating Water

The process of extracting water from seawater is called desalination. This process involves capturing evaporated water from the seawater solution.


The process of removing water from a solution is called dehydration. The solvent (water) is separated from the solution using evaporation. Many foods come in dehydrated forms to increase shelf-life.


Sometimes it is necessary to recover the solvent and solute, or simply separate the solution and recover both elements. This process is called distillation.

Processing Petroleum

When petroleum is extracted from the ground it is not a pure element. The process of breaking up petroleum to its pure elements is called fractional distillation. In this process, the mixture is heated up til one element begins to change state to a gas (vaporization). It travels away from the original mixture (and the heat source) until it cools into a liquid state (recondenses). This liquid is collected in a container, and the process is repeated for the next element. The reason this works is because the boiling point of each element is different. In Canada we use Fractionating towers to separate petroleum mixtures.

The shorter tower vaporizes the mixture completely into the larger tower. Because each pure element has different properties, they recondense at different levels of the tower.

Solid Mixtures

Solid mixtures, such as ore, are made up of different solid substances. It is still possible to separate these mixtures even though there is no fluid. For example, gold ore contains white quartzite and yellow gold. The gold extraction process looks like the following: (1) crush the ore into a fine powder, (2) dissolve the gold in a chemical mixture, (3) use a filter to separate the dissolved gold from the quartzite, (4) release the gold from the solution by adding zinc. Anything caught by the filter is called solid waste.

Another example of this process is used when creating different types of sugar.

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