In this post, we will learn how to separate a mixture of sand and copper(II) sulfate solution using two important techniques: filtration and crystallisation.
Soluble and Insoluble Substances in Water
Some solids dissolve in water (soluble), while others do not (insoluble). What do we mean by that?
- Sand is insoluble in water. It does not dissolve. If we leave it to stand, sand will settle at the bottom of the water. We can separate sand from water using a physical method, called filtration.
- Copper(II) sulfate is soluble in water. It dissolves to form a blue solution. Because copper(II) sulfate is soluble, we cannot simply filter to separate the solute from the solvent. We will have to carry out crystallation to obtain the solid salt.
Step 1: Filtration (To Separate Sand)
We have a mixture of sand and copper(II) sulfate solution. There are 3 components in this mixture – we have sand, copper(II) sulfate salt and water.
Filtration is used to separate an insoluble solid from a liquid. We can first start by carrying out filtration to separate the sand from copper(II) sulfate solution.
Procedure:
- Pour the mixture of sand and copper(II) sulfate solution through filter paper placed in a funnel.
- The sand particles (which are larger than the pores of the filter paper) remain on the filter paper. This is called the residue.
- The copper(II) sulfate solution passes through the filter paper. This is called the filtrate.
After filtration, we have successfully separated the sand from the copper(II) sulfate solution.
Step 2: Crystallisation (To Obtain Copper(II) Sulfate Crystals)
Many salts are soluble in water. Copper(II) sulfate salt is one of them. To obtain the pure solid salt from the solution, we carry out crystallisation.
Crystallisation is a physical method used to obtain a soluble solid (solute) from its solution.
Procedure:
- Heat the filtrate (copper(II) sulfate solution) gently until it becomes saturated. (A saturated solution is one that cannot dissolve any more solute.)
- To test if the solution is saturated, dip a clean glass rod into the solution. As the solution cools, saturated solution should leave small crystals on the rod. If not, we will need to continue heating until it is saturated.
Caution: Do not overheat the solution. Overheating can produce white anhydrous copper(II) sulfate instead of blue crystals. - Once saturated, allow the solution to cool slowly without stirring or shaking.
- Blue crystals of copper(II) sulfate will form.
- Filter the crystals to collect them.
- Wash the crystals with a small amount of cold water to remove any remaining impurities. Cold water is used because copper(II) sulfate is less soluble in cold water.
- Dry the crystals between filter papers.
Summary
- Use filtration to separate an insoluble solid (sand) from a liquid.
- Use crystallisation to obtain a soluble solid (copper(II) sulfate crystals) from its solution.
- These two techniques are commonly used in the laboratory to separate mixtures.
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