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wise otter.Chemistry
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K326 / K328 / 2027
Data and Experimental Skills

Lesson 8 of 8

Separation and recovery

Choose what to retain and how to recover it.

O-Level 5086 / 5088 (2026) / SEC G3 K326 / K328 (2027)

  • I can explain paper chromatography.Syllabus

    Syllabus K326 / K328, Practical(e). Paper chromatography

  • I can explain filtration.Syllabus

    Syllabus K326 / K328, Practical(f). Filtration

Recover the substance you need

Choose a process from solubility, volatility and thermal stability.

The question determines what to keep
TaskMethodWhat is recovered
Remove an insoluble solid from a liquidFiltrationSolid is the residue; liquid passing through is the filtrate
Obtain a dissolved solid that crystallises on coolingConcentrate, cool, filter crystals, wash sparingly and dryCrystals; some solute remains dissolved in the mother liquor
Recover a solventSimple distillationCondensed vapour from the distillate; monitor the apparatus correctly
Compare soluble mixture componentsPaper chromatographySeparated spots, compared under the same conditions

For paper chromatography, use a pencil baseline above the solvent, small concentrated spots and a covered vessel where appropriate. Remove the paper before the solvent reaches the top and mark the solvent front immediately.

Combined practical assessment includes chromatography and filtration, and explicitly does not require describing salt-preparation methods. Use the shared separation ideas here; the salt-preparation routes appear only in the Pure view.

Check your understanding

Why is a filtered insoluble precipitate washed with a little distilled water?

  1. To rinse away soluble impurities left from the solution it was made in.
  2. To cool the precipitate, so that it can be weighed straight away.
  3. To dissolve the precipitate partly, so that its crystals become larger.
Show the answer

To rinse away soluble impurities left from the solution it was made in.

The solid is coated with the solution it formed in, which contains soluble ions. A small amount of cold distilled water removes them without dissolving much of the product.