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Separating iron filings, salt and
sand
Separating iron filings, salt and sand is one of the most interesting
experiments that can be undertaken by students investigating the principles
of separation of materials.
In this topic, you will be taken through the experiment and the theory
used.
Separation theory
Generally, materials are separated according to
differences in their physical properties. During the separation process,
it is important not to chemically change any of the parts of the mixture
if possible. This avoids costly chemical processes and loss of material.
It is best to try to separate one component at a time, which means that
this experiment can be expected to have at least three stages, corresponding
to the removal of each component from the mixture.
Physical properties
In this experiment, the three constituent materials in the mixture are
solids with significantly different physical properties, which makes
separation easier.
- Iron is a magnetic solid which is insoluble in water.
- Salt is a non-magnetic solid which is soluble in water.
- Sand is a non-magnetic solid which is insoluble in water.
 
Their individual properties are best set out as a table:
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Material
|
State
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Magnetic
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Water Soluble
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Iron
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Solid
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Yes
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No
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Salt
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Solid
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No
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Yes
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Sand
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Solid
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No
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No
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Separation technique
theory
In deciding how to separate two or more materials, you should first
look for a difference in a physical property.
- In this case all three are solids, which means
that differences in state are of no use.
- Iron is magnetic and the other two not, which
means a magnet could be used to attract the iron filings out of the
mixture, leaving the salt and sand.
- Salt is water soluble, while sand is not. This
means the two can be mixed in water and stirred. The salt will dissolve
and the sand will not.
- These differences form the basis for separation
of the three materials.
Separation technique
Before you prepare the mixture, weigh each of the
three solids and record the weights for reference at the end of the
experiment.
- Wrap a magnet in
plastic lunch wrap and move it through the mixture of the three solids.
The iron filings will stick to the magnet. The filings can be removed
by unwrapping the plastic from the magnet carefully!
- Mix the remaining
salt and sand in water and stir. Make sure you have used enough water
to dissolve all of the salt, but not too much that handling large
quantities of salt water becomes a problem.
- Using a funnel, flask and filter paper, filter
off the sand from the salt water solution. Wash the sand with some
fresh water to remove the last of the salt from the sand in the filter
paper.
- Put the sand to one side and allow it to dry
in the Sun or warm oven.
- Collect all the salt water in a weighed container
and evaporate off the water. This may take some time in the Sun or
may be sped up in an oven.
- Weigh each of the
separated solids and compare them with their original weights. Give
a prize for the best set of results.
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