A7LAM CSCA ACADEMYCSCA Academy / Chemistry / Experiments and applications
CSCA Chemistry · Lesson 20 of 21Separation and purification
Séparation et purification · الفصل والتنقية
▶ Watch the video lesson (A7LAM students)
Choose a separation method from the property that differs: particle size, boiling point, solubility or density.
Key ideas
- Filtration: an insoluble solid from a liquid.
- Evaporation and crystallisation: a dissolved solid from its solution.
- Distillation: liquids with different boiling points, or pure water from salt water.
- Extraction with a separating funnel: the solute moves into a second solvent that does not mix with the first.
Formulas to know
- Filtration: paper against the funnel, liquid below the paper's edge, funnel tip touching the beaker
- Distillation: thermometer bulb at the side arm; condenser water in at the bottom
- Purify without adding new impurities
Worked example
How do you separate sand and salt from a mixture?
- Dissolve: add water; the salt dissolves, the sand does not
- Filter: the sand stays on the filter paper
- Evaporate: heat the filtrate to get salt crystals
Answer: Dissolve, filter, evaporate
Practice questions
1. Best method to get pure water from sea water?
Filtration · Distillation ✓ · Extraction · Decanting
Water boils off and condenses; salt stays.
2. Iodine is removed from water with CCl₄. This is:
distillation · extraction ✓ · filtration · crystallisation
Iodine moves into the CCl₄ layer.
3. In distillation the thermometer bulb goes:
in the liquid · at the side-arm opening ✓ · in the condenser · in the collecting flask
It measures the vapour leaving.