There are various ways to separate solids from liquids, depending on how they are mixed together. If a solid retains its own distinctive form within the liquid, this is known as a heterogeneous mixture and you may be able to separate the solid from the liquid by decanting or filtering the mixture. If the solid dissolves in the liquid it forms a homogenous mixture or solution. You may be able to separate the solid from the liquid by evaporating the liquid or distilling the solution. Some industrial processes use other methods such as centrifugal separation, where the denser solids are separated from the liquid by spinning the mixture in a centrifuge. This is more difficult to recreate in a home or classroom environment however.
Mix sand and water in a beaker and allow to settle. As the sand is denser than the water it will eventually sink and settle on the bottom. This is known as sedimentation.
Carefully tip the beaker and pour the water into another container. If the sand rises or the water starts to cloud, leave the mixture to settle again.
Repeat the process until you have poured off as much water as possible. Decanting does not usually separate the solid from the liquid completely as it is almost impossible to get all the water out without losing some of the sand.
Put a pan of water on the cooker to boil. Add pasta when the water is boiling. When the pasta is cooked, place a colander on top of another large pan. Pour the water and pasta into the colander. The water will drain into the second pan and the pasta will remain in the colander. This is a simple, everyday example of filtration.
Mix sand and water in a beaker. Take a sheet of filter paper and fold it into a cone shape. Place the paper into the mouth of a funnel and place the funnel stem into another beaker.
Pour the mixture of sand and water slowly into the funnel. The water will drain into the second beaker and the sand will remain on top of the filter paper.
Mix salt and water in a beaker and stir until the salt dissolves. Transfer into a pan and put on the cooker to boil. All the water will eventually evaporate, leaving salt crystals in the bottom of the pan. This is an easy way to separate solids and liquids from a solution but you will lose the liquid as it evaporates. You can retain both the solid and liquid by distilling the solution.
Set up a simple still. The easiest way to do this is to put the solution in a conical flask. Put a rubber stopper in the top of the flask with a whole for a rubber tube. Place the flask above a Bunsen burner or other heat source and place the other end of the tube in another flask or beaker. This should be on a lower level than the flask containing the solution.
Apply heat and let the solution boil. The liquid will evaporate and travel through the tube, condensing back into liquid in the other container. When all the water has been transferred in this way, the salt crystals will be left in the original flask.
Things you need
- 2 beakers
- Bunsen burner
- 2 conical flasks
- Rubber stopper and tube