Lesson 7 of 7

Separation and recovery

Choose what to retain and how to recover it.

SEC G2 Science K223 / K225 (2027)

I can select and use techniques, apparatus and materials.Syllabus
Syllabus K223 / K225, C1. Select and use techniques, apparatus and materials

Recover the substance you need

Choose a process from solubility, volatility and thermal stability.

The question determines what to keep
Task	Method	What is recovered
Remove an insoluble solid from a liquid	Filtration	Solid is the residue; liquid passing through is the filtrate
Obtain a dissolved solid that crystallises on cooling	Concentrate, cool, filter crystals, wash sparingly and dry	Crystals; some solute remains dissolved in the mother liquor
Recover a solvent	Simple distillation	Condensed vapour from the distillate; monitor the apparatus correctly
Compare soluble mixture components	Paper chromatography	Separated 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.

Check your understanding

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

To rinse away soluble impurities left from the solution it was made in.
To cool the precipitate, so that it can be weighed straight away.
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.

G2 practical work includes crystallisation of salts, filtration, paper chromatography and distillation. Describing the full preparation of a pure salt is not required.