Skip to content
Oak National Academy
Oak National Academy
Teachers
Pupils
New
New
Year 7

Separating pure salt from dirty rock salt

I can suggest how to combine separation techniques in order to separate pure salt from a sample of rock salt.

Download all resources
Share activities with pupils
New
New
Year 7

Separating pure salt from dirty rock salt

I can suggest how to combine separation techniques in order to separate pure salt from a sample of rock salt.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. The properties of the substances in a mixture help to determine the technique best suited to separate them.
  2. When mixtures contain more than two components, multiple techniques may be needed to separate them.
  3. Creating a solution of an existing mixture can allow a specific technique to be used for separation.
  4. Separating salt from rock salt requires: making a solution, filtration, and crystallisation.

Common misconception

Filtration alone can separate salt from rock salt - idea that only one technique is needed.

Highlight that each separation technique (so far) creates two products; one of them may still be a mixture that requires further separation.

Keywords

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

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

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

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

If you don't have rock salt, create a mixture of salt & sand. For added fun, add a few anti-bumping granules to act as 'jewels' and challenge pupils to further separate the jewels too.
Teacher tip

Content guidance

  • Depiction or discussion of sensitive content
  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

Skip video

Loading...

Starter quiz

Download starter quiz

6 Questions

Q1.
True or false? If a substance is described as 'soluble', then it means it can be dissolved in a solvent.
Correct answer: True
False
Q2.
Which of the following can filtration be used for in the context of separating mixtures?
To dissolve all components.
Correct answer: To separate insoluble substances from soluble substances.
To change the colour of the mixture.
To increase the temperature of the mixture.
Q3.
Which of the following properties is not a physical property?
colour
boiling point
shiny or dull
Correct answer: flammability
Q4.
Which property is most important when choosing a solvent to dissolve a substance?
The colour of the solvent.
The boiling point of the solvent.
Correct answer: The solubility of the substance in the solvent.
The smell of the solvent.
Q5.
Substances that do not dissolve in a liquid are described as ...
Correct Answer: insoluble, insoluble.
Q6.
True or false? Crystallisation is a process that only occurs at high temperatures.
True, as crystallisation requires high temperatures to form crystals.
True, because it only happens when a solution is boiled.
Correct answer: False, as crystallisation can occur at many temperatures, even during cooling.
False, because crystallisation does not involve temperature changes.

Exit quiz

Download exit quiz

6 Questions

Q1.
Put the following steps in the correct order to separate salt from rock salt.
1 - Crush the rock salt into smaller pieces.
2 - Add water to the rock salt to dissolve the salt.
3 - Filter the rock salt and water mixture to remove insoluble substances.
4 - Collect the filtrate (water and salt solution).
5 - Evaporate the water to leave salt crystals.
Q2.
The process of producing solid crystals by evaporating the solvent from a saturated solution is called ...
Correct Answer: crystallisation, crystallization, crystallisation.
Q3.
When a substance dissolves in a liquid it is described as in that liquid.
Correct Answer: soluble
Q4.
Which of these statements best describes the purpose of creating a solution in the separation process of pure salt from rock salt?
To make the process longer.
Correct answer: To dissolve the soluble component for easier separation.
To change the chemical properties of the components.
To make filtration unnecessary.
Q5.
True or false? Sand, being insoluble in water, can be completely removed from rock salt using crystallisation.
True
Correct answer: False
Q6.
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.
Correct Answer: saturated