Evaporation, Condensation and Separation
Section: Chemistry | Syllabus: Cambridge Primary Stage 5 Science (0097)
Evaporation and Condensation
- Evaporation and condensation are opposite changes of state, and both can be explained using the particle model.
Evaporation and condensation are opposite changes between liquid and gas
| Process | Change | Particle explanation |
|---|---|---|
| Evaporation | Liquid → gas | Particles gain energy, move faster and some escape from the surface |
| Condensation | Gas → liquid | Particles lose energy, slow down and move closer together |
- A higher temperature usually makes evaporation happen faster.
- Condensation is the reverse of evaporation.
Dissolving Is Reversible
- Dissolving is a reversible change because the solute and solvent can be separated again.
- To recover a dissolved solid, heat or leave a solution so that the solvent evaporates
- the dissolved solid remains behind and may form crystals
- if the solvent must also be collected, the escaping vapour can be cooled so it condenses back into a liquid
- Always heat gently and follow safety precautions when separating a solution.
Gently evaporating the solvent leaves the dissolved solid behind
Worked Example: Recovering a Dissolved SolidQuestion: Describe how to obtain sugar from a sugar solution. [2]
Sugar is the non-evaporating solute and water is the solvent. Allow the water to evaporate gently so the sugar remains. AnswerPlace the solution in an evaporating dish and gently heat it, or leave it in a warm place. The water evaporates and sugar remains.
Common Mistakes
MistakeEvaporation changes gas into liquid.
FixEvaporation is liquid to gas; condensation is gas to liquid.
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