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Year 7

Separating a soluble solid from a liquid

I can explain how dissolving can be reversed to separate a soluble solid from a liquid.

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New
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Year 7

Separating a soluble solid from a liquid

I can explain how dissolving can be reversed to separate a soluble solid from a liquid.

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Share activities with pupils
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Lesson details

Key learning points

  1. Evaporation can remove solvent from a solution, leading to the production of a saturated solution.
  2. Crystallisation reforms a solute as crystals from a saturated solution following a change in conditions.
  3. Solvents evaporate into the air around you during the process of crystallisation.
  4. Larger crystals form when the solvent evaporates more slowly.
  5. Heating a solution makes the solvent evaporate more quickly.

Keywords

  • Solute - A solute is a substance that has dissolved into a solvent.

  • Solvent - A solvent is a liquid into which a solute dissolves.

  • Evaporation - Occurs when a substance's particles are in the liquid state at its surface with enough energy to change to the gas state and mix with air.

  • Crystallisation - A process that forms solid crystals from a saturated solution by evaporating the solvent.

  • Crystal - A crystal is a solid whose particles are arranged in a highly ordered, repeating pattern.

Common misconception

Pupils sometimes use the terms evaporation and boiling interchangeably, but they are not the same.

Boiling: a liquid substance is heated & gas bubbles form. Evaporation: same, BUT only on the surface of the liquid & the gas mixes with air.

Try contextualising crystallisation by looking at its process and results in nature (Cueva de los Cristales, Mexico) and art (Roger Hiorns, 'Seizure').
Teacher tip

Content guidance

  • 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).

Lesson video

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Starter quiz

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6 Questions

Q1.
What process happens when a solid can be observed to 'disappear' in a liquid to make a solution?
boiling
condensing
melting
Correct answer: dissolving
evaporating
Q2.
When a process is able to go backwards, or be "undone", it is said to be .
Correct Answer: reversible
Q3.
Match the word to the definition.
Correct Answer:soluble,When a solid can dissolve in a liquid

When a solid can dissolve in a liquid

Correct Answer:insoluble,When a solid cannot dissolve in a liquid

When a solid cannot dissolve in a liquid

Correct Answer:solution,The mixture formed when a solid dissolves in a liquid

The mixture formed when a solid dissolves in a liquid

Correct Answer:saturated,When no more solid can dissolve

When no more solid can dissolve

Q4.
Put the following changes of state for ice/water in order starting from the one that requires the lowest temperature to the one that requires the highest temperature.
1 - Melting
2 - Evaporating
3 - Boiling
Q5.
A volume of salt solution containing 0.5 g of salt was placed in a beaker and left for 2 weeks on the windowsill, after which only crystals of salt remained. How much salt would be present?
0.0 g
0.25 g
0.4 g
Correct answer: 0.5 g
Q6.
Sugar was added to water at 60℃ until no more sugar could dissolve. The solution was left to cool. What would you expect to see and why?
No change as the sugar would still be dissolved.
No change as temperature does not affect the solubility of the sugar.
Solid sugar would start to form as the water would evaporate.
Correct answer: Solid sugar would start to form as it is less soluble at a lower temperature.

Exit quiz

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6 Questions

Q1.
What is a solute?
Correct answer: A substance that has dissolved into a solvent.
A liquid into which a solute dissolves.
A solid whose particles are arranged in an irregular pattern.
A substance that undergoes evaporation.
Q2.
Dissolving is a process as solute can be added to the solvent and the solvent can then be evaporated to recover the solute.
Correct Answer: reversible
Q3.
Which definition best describes evaporation?
Forms solid crystals from a saturated solution.
Change from the liquid state to the gas state occurring at the boiling point.
Correct answer: Change from the liquid state to the gas state occurring below the boiling point.
Forms solid crystals from a dilute solution.
Q4.
What happens to the size of crystals formed during crystallisation if the solvent evaporates slowly?
The crystals are smaller.
The crystals remain the same size.
Correct answer: The crystals are larger.
The crystals disappear.
Q5.
What is the name of the process that forms solid crystals from a saturated solution by evaporating the solvent?
Correct Answer: crystallisation
Q6.
Solvents evaporate into the air during crystallisation. How does heating affect this process?
It has no effect.
It slows the process down.
Correct answer: It speeds up the process.