Separation theory
Physical properties
Separation technique theory
Separation technique |
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.
Are you looking for experiments that are more accessible to younger students? Try the free downloadable Primary Connections unit All mixed up, targeted at Year 2 students learning about combining and separating different materials.
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:
|
Material
|
State
|
Magnetic
|
Water Soluble
|
|
Iron
|
Solid
|
Yes
|
No
|
|
Salt
|
Solid
|
No
|
Yes
|
|
Sand
|
Solid
|
No
|
No
|
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.
| Copyright owned by the State of Victoria (Department of Education and Early Childhood Development). Used with Permission. |  |
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