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Science

Separating Mixtures

Overview

Students investigate different ways to separate mixtures — filtering, evaporating, and sieving — and match the method to the mixture.

Learning Objective
Students understand that mixtures can be separated using appropriate techniques and can select the right method for a given mixture.

Resources needed

  • Soil and water
  • Salt and water
  • Sand and gravel
  • Cloth as a filter
  • Containers

Lesson stages

0 / 7 done
  1. 1 Mix soil and water in a container. Ask: how could you separate them?
  2. 2 Filter through cloth — soil stays, water passes through.
  3. 3 Dissolve salt in water — you cannot filter it. Ask: how to get the salt back?
  4. 4 Leave the salt water in the sun — water evaporates, salt remains.
  5. 5 Mix sand and gravel — sieve separates by particle size.
  6. 6 Ask: which method works for each mixture and why?
  7. 7 Introduce: the right separation technique depends on the properties of the mixture.

Tap a step to mark it as done.

Variations

  • Evaporate sea water and taste the residue — is it salt?
  • Use layers of different soil types to filter muddy water.
  • Separate iron filings from sand using a magnet.
More information

Teach: mixture, separate, filter, evaporate, dissolve, sieve, residue, solution. Key question: 'What property of the mixture allows this separation method to work?'

Focus on one method — filtering — before introducing evaporation and sieving.

Can students select and justify the correct separation technique for a given mixture? Can they explain why filtering does not work for a dissolved substance?

Soil, water, salt, and cloth are all free or very cheap. Sand and gravel are available outdoors.

Students often think filtering will separate a dissolved substance like salt from water. Dissolved particles are too small to be caught by any filter — they pass through at the molecular level.

Separating mixtures introduces the distinction between mixtures and compounds, and between physical and chemical changes. It has direct real-world applications in water purification, mining, and food production.

Activity details
Primary Medium 25 minutes 10 minutes prep Small Group Indoor & Outdoor
Topics
Mixtures Separation Chemistry