Discover: Hold the Salt

Separating homogeneous mixtures is usually more work because the solute has become dissolved in the solvent. That means you need to find some way of separating all the tiny intermingled particles.

Consider a solution of salt water. The salt particles are dissolved and mixed completely with the water particles. They are too small to see and pick out. They are too small to filter. None of the previous methods you used for heterogeneous mixtures will work on solutions. What is left?

Distillation is a method used to separate substances that have different boiling points. The mixture is heated and one substance is evaporated (or boiled away) from another and then collected. Often, this process is used to purify mixtures and solutions.

For example, tap water contains all sorts of impurities although it is fit to drink! You can separate the impurities and get pure water by boiling tap water, collecting the steam, and allow it to cool and become water again (condensation). The result is distilled water.


Compare:

  • In the distillation method, water turns into gas at its boiling point whereas, in evaporation, water turns into gas below its boiling point.
  • The distillation process takes place throughout the whole liquid mass. The evaporation process occurs only at the surface of the liquid. 
  • At the boiling point of the distillation process, the liquid forms bubbles. There are no bubbles formed in evaporation.
  • Distillation is a separation or purifying technique, but evaporation is not necessarily so.

  Video

Distillation is used in laboratories and industries when very careful separation is needed or it may be done on your stove.


For an explanation on how to complete the experiment below, watch this video on the Solar Water Purifier.   


How can fresh, drinkable water be produced from a saltwater solution?

Materials
  • large bowl
  • heavy glass cup
  • teaspoon
  • clear plastic food wrap
  • any coin
  • clear cellophane tape
  • blue food colouring
  • salt
Will the water in this experiment be evaporated or distilled?

Notebook

Click here to download the instructions for this activity. Save this file to your Chemistry Notebook.

  Technology Connection

The concern that we may be using all the clean fresh water is increasing. In some desert areas, for example, seawater is converted to fresh drinking water through the process of desalination.

Desalination is similar to the evaporation process you performed in the Hold the Salt Activity.

View the How Stuff Works Website to read more about this.

Capetown, South Africa gathers rain water for its 44 million people. However, because of a 3 year drought, this water is not enough. It has even become illegal to drill wells. Capetown is building a large desalination plant, but it may run out of water before the plant is built. What happens then? Read these news articles from Jan. - Mar. 2018 and play the water saving simulation game from the city of Capetown. How good are you at saving water?