Separating iron filings, salt and sand
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.

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.

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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.
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  1. 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!



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  2. 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.




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  3. 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.


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  4. Put the sand to one side and allow it to dry in the Sun or warm oven.



  5. 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.

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  6. 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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