A process or method used to isolate a substance from a mixture, usually to obtain a pure sample of it.

A property is a feature or characteristic of a substance that can be used to classify it, or describe how it behaves.

When a substance dissolves in a liquid it is described as soluble in that liquid.

An insoluble substance is one that will not dissolve in a particular solvent.

Separating pure salt from dirty rock salt

Science

In the Understanding Chemical Reactions unit, pupils will build on their understanding of physical changes to learn how atoms rearrange to form new substances during chemical reactions (chemical changes).

In the key stage 2 Properties, changes and separating materials unit, pupils learnt about mixtures, including solutions, and separation techniques including filtering and evaporation.

This unit covers techniques for separating mixtures, including filtration, evaporation, distillation, and chromatography, as well as identifying pure substances. Conduct experiments safely, record observations, evaluate methods, and suggest improvements.

Separation techniques

Physical activity and equipment requiring safe use

Add water to the rock salt to dissolve the salt.

Filter the rock salt and water mixture to remove insoluble substances.

Collect the filtrate (water and salt solution).

Evaporate the water to leave salt crystals.

Put the following steps in the correct order to separate salt from rock salt.

The process of producing solid crystals by evaporating the solvent from a saturated solution is called ...

When a substance dissolves in a liquid it is described as {{}} in that liquid.

To dissolve the soluble component for easier separation.

To change the chemical properties of the components.

Which of these statements best describes the purpose of creating a solution in the separation process of pure salt from rock salt?

True or false? Sand, being insoluble in water, can be completely removed from rock salt using crystallisation.

When dissolving salt into water, the solution will reach a point where no more salt can be dissolved at a given temperature. When no more solute can be dissolved we have made a {{}} solution.

True or false? If a substance is described as 'soluble', then it means it can be dissolved in a solvent. 

To separate insoluble substances from soluble substances.

To increase the temperature of the mixture.

Which of the following can filtration be used for in the context of separating mixtures?

Which of the following properties is **not** a physical property?

The solubility of the substance in the solvent.

Which property is most important when choosing a solvent to dissolve a substance?

Substances that do not dissolve in a liquid are described as ...

True, as crystallisation requires high temperatures to form crystals.

True, because it only happens when a solution is boiled.

False, as crystallisation can occur at many temperatures, even during cooling.

False, because crystallisation does not involve temperature changes.

True or false? Crystallisation is a process that only occurs at high temperatures.

Content guidance

Risk assessment required - equipment

Adult supervision required

This lesson will be removed by end of Summer Term 2025.

Separating pure salt from dirty rock salt

Lesson outcome

Content guidance

This lesson will be removed by end of Summer Term 2025.