How To Separate Salt and Sand

Separating Soluble and Insoluble Components of a Mixture

Sea salt is collected from evaporating it onto beaches, but it's still necessary to purify the salt by removing the sand residue.
Sea salt is collected from evaporating it onto beaches, but it's still necessary to purify the salt by removing the sand residue. GTW / Getty Images

One practical application of chemistry is that it can be used to help separate one substance from another. The reasons materials may be separated from each other is because there is some difference between them, such as size (separating rocks from sand), state of matter (separating water from ice), solubility, electrical charge, or melting point. Technically you could get a magnifying glass and tweezers and eventually pick out particles of salt and sand, but there's a better way.

 The difference in solubility is an efficient way to separate the components of this mixture. 

If a substance is soluble it means it dissolves in a solvent. Salt (sodium chloride or NaCl) is soluble in water. Sand (mostly silicon dioxide) is not.

Separating Salt and Sand

  1. Pour the salt and sand mixture into a pan.
  2. Add water. You don't need to add a lot of water. Solubility is a property that is affected by temperature, so more salt dissolves in hot water than cold water. It's okay if the salt doesn't dissolve at this point.
  3. Heat the water until the salt dissolves. If you get to where the water is boiling and there is still solid salt, you can add a bit more water.
  4. Remove the pan from heat and allow it to cool until it's safe to handle.
  5. Pour the salt water into a separate container.
  6. Now collect the sand.
  7. Pour the salt water back into the empty pan.
  8. Heat the salt water until the water boils. Continue boiling it until the water is gone and you're left with the salt.

    Another way you could have separate the saltwater and sand would be to stir up the sand/saltwater and pour it through a coffee filter to capture the sand.

    Notes and Questions

    Note, you could have simply let the water evaporate from the pan until you were left with the salt. If you had chosen to evaporate the water, one way you could have sped up the process would have been to pour the saltwater into a large, shallow container.

    The increased surface area would have exchanged the rate at which water vapor could have entered air.

    The salt did not boil away with the water. This is because the boiling point of salt is much higher than that of water. The difference between boiling points can be used to purify water via distillation. In distillation, the water is boiled, but is then cooled so it will condense from vapor back into water and can be collected. Boiling water separates it from salt and other compounds, like sugar, but it has to be carefully controlled to separate it from chemicals that have lower or similar boiling points.

    While this technique can be used to separate salt and water or sugar and water, it would not separate the salt and sugar from a mixture of salt, sugar, and water. Can you think of a way to separate sugar and salt?

    Ready for something more challenging? Try purifying salt from rock salt.