To evaporate salt from sand, you first separate the sand from the salt by dissolving the salt in water and filtering out the insoluble sand. Afterward, you heat the remaining salt solution to evaporate the water, leaving the pure salt behind.
The Process of Separating Sand and Recovering Salt
This method leverages the different physical properties of sand and salt: salt (sodium chloride) is soluble in water, while sand (primarily silicon dioxide) is not. This difference allows for their effective separation using a combination of dissolution, filtration, and evaporation.
Step-by-Step Procedure
The process is straightforward and can be conducted with basic laboratory equipment. Based on standard laboratory practices and the provided reference from the Royal Society of Chemistry, here's how to do it:
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Prepare the Mixture:
- Pour the sand–salt mixture into a beaker so that it just covers the base. This ensures there's enough space for the added water and stirring.
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Dissolve the Salt:
- Add about 50 cm³ of water, or add water until the beaker is about one-fifth full. Water acts as a solvent for the salt.
- Stir the mixture gently for a few minutes. This ensures that all the salt thoroughly dissolves in the water, forming a salt solution, while the sand remains undissolved at the bottom.
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Filter the Sand:
- Set up a filtration apparatus, typically consisting of a funnel lined with filter paper placed over a conical flask.
- Filter the mixture into the conical flask. The sand, being insoluble, will be trapped by the filter paper (the residue), while the salt solution (now called the filtrate) will pass through the filter paper into the conical flask below. This effectively separates the sand from the salt solution.
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Prepare for Evaporation:
- Carefully pour the filtrate (the clear salt solution) from the conical flask into an evaporating basin. An evaporating basin has a wide surface area, which helps in faster evaporation.
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Evaporate the Water:
- Place the evaporating basin on a tripod stand with a gauze mat, and gently heat it using a Bunsen burner or a hot plate.
- As the water heats up, it will reach its boiling point and turn into steam, escaping into the atmosphere.
- Continue heating until all the water has evaporated. As the water level decreases, solid salt crystals will begin to appear and accumulate in the basin. You may need to reduce the heat towards the end to prevent the salt from splattering or decrepitating due to rapid heating.
- Once all the water has evaporated, only the dry, solid salt will remain in the evaporating basin.
Why This Method Works
This separation technique is highly effective due to the distinct physical properties of sand and salt:
- Solubility: Salt is soluble in water, forming a homogeneous solution. Sand is insoluble, remaining as a heterogeneous mixture.
- Particle Size: Sand particles are large enough to be trapped by filter paper, while dissolved salt molecules are not.
- Boiling Points: Water has a relatively low boiling point (100°C), allowing it to evaporate easily, leaving behind the salt which has a much higher melting/boiling point.
This method is a classic example of how understanding material properties can be applied to effectively separate components of a mixture.
