In this lesson students learn that solutions are homogeneous mixtures composed of a solute and a solvent and identify techniques to separate substances in a mixture.
Show the students three glasses of water and tell them one glass has tap water, one has salt water, and one has river/creek/dam (muddy) water. Ask them which glass of water they would drink and why. Inform students that tap water is a mixture that has had harmful and bad tasting components removed. It could have started out as salt water or dam/river water and they are going to learn about separation techniques that are used to produce clean water.
- Review the definition of a mixture from lesson 1.
- Introduce and define the term ‘solution’ and classify tap water and salt water as solutions. Ask the students why the muddy water is not a solution.
- Define the terms ‘solute’ and ‘solvent’ relating to tap water and salt water.
- Explain that there are many different separation techniques that are used to separate mixtures and the technique used depends on what needs to be recovered. View the learning object Making water drinkable: mixtures.
- Describe ‘distillation’ and view the animation Distillation or demonstrate the technique. Explain the Sun’s energy can be used for distillation using a solar still. Discuss everyday applications of distillation.
- Describe ‘evaporation’ as a separation technique and compare to distillation. Discuss everyday applications of evaporation.
- Describe ‘filtration’ and view the video clip Filtration.or demonstrate the technique. Discuss everyday applications of filtration.
- Conduct an investigation using distillation and filtration techniques. Provide students with the worksheet Investigating distillation and filtration (Word, 387 KB). Discuss the effectiveness of each technique.
Review separation techniques using the learning object Grumpy in the desert.