Class notes for Mixtures and Methods of Separation - Science AQA GCSE Chemistry Student Book

Mixtures and methods of separation
Mixtures vs. compounds
 Mixture: made up of two or more substances that are NOT chemically
combined together
 Compounds are made up of two or more elements which ARE chemically
combined together




How to separate mixtures
 Filtration
- This is used to separate substances that are
insoluble (e.g. sand) in a particular solvent (water)
from that that are soluble (salt) in solvent
- You would put the solution through filter paper
which would leave sand on top but salt water
would be filtered out with the water into the
beaker
- The sand you collect (the filtrate) should be
washed with distilled water to remove any salt
solution left on it and the wet sand is then dried in
a warm oven to evaporate off any remaining water
in the sand to leave pure, dry sand
 Crystallisation
- Separates a soluble solid from a solvent
- If you then wanted to obtain a pure sample of the
soluble solid (e.g. salt) from the solvent (e.g.
water) you would need to evaporate the water off
- The best way to do this is heating the solution in
an evaporating dish on a water bath
- Stop heating when the solution is at the point of
crystallisation which is when small crystals first
appear around the edge of the solution/when
crystals appear in a drop of solution extracted
from the evaporating dish
- The rest of the water is left to evaporate at room
temperature
 Distillation