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Grades 7–9 Intermediate About 20 min Version 1 Awaiting review Premium

Getting salt back from a salt and sand mixture

Rock salt from a mine is mixed with sand and grit. No single method can separate it, but you can use the different properties of salt and sand one step at a time. Salt dissolves in water and sand does not, so dissolving followed by filtration removes the sand. Evaporating the water then leaves the salt behind. Evaporating slowly lets the salt form crystals, which is called crystallization.

What you will learn

  • Plan a sequence of methods to separate a mixture.
  • Explain which property of salt or sand each step uses.
  • Describe how crystals form when a solution is evaporated.

Before you start

  • Know about dissolving, filtration and evaporation.

Materials

  • Salt
  • Sand
  • Water (50 mL in Beaker A)

Equipment

  • Beaker
  • Conical flask with funnel and filter paper
  • Evaporating dish
  • Hot plate
  • Stirring rod

Procedure

  1. Add salt and sand to the water in Beaker A and stir until the salt dissolves.
  2. Filter Beaker A into Flask B. The sand stays on the filter paper.
  3. Pour the clear filtrate from Flask B into Dish C.
  4. Heat Dish C gently and use the timer until all the water has evaporated.

How this simulation is simplified

  • Evaporation times are shortened to a few minutes.
  • All the salt dissolves and passes through the filter paper, and all the water passes into the flask.