Evaporation & Crystallisation
If we have a mixture of a solid and a liquid will be able to separate them using filtration, evaporation or crystallisation. Filtration is used when the solid is insoluble (not able to be dissolved), and evaporation or crystallisation is used when the solid is soluble (able to be dissolved).
Filtration – Insoluble Solid
Filtration is used when the solid is insoluble, which means that the solid does not dissolve in a liquid. We are able to separate the insoluble solid from a liquid by pouring the mixture through a funnel that is lined with filter paper. The filter paper will allow the liquid to pass through but will not allow the insoluble solid through. This means that the insoluble solid will be left on the filter paper. The solid that is left on the filter paper is known as the residue and what passes through the filter paper is known as the filtrate. The apparatus will be set up like the diagram below.
Filtration is used when the solid is insoluble, which means that the solid does not dissolve in a liquid. We are able to separate the insoluble solid from a liquid by pouring the mixture through a funnel that is lined with filter paper. The filter paper will allow the liquid to pass through but will not allow the insoluble solid through. This means that the insoluble solid will be left on the filter paper. The solid that is left on the filter paper is known as the residue and what passes through the filter paper is known as the filtrate. The apparatus will be set up like the diagram below.
An example would be the filtering of a mixture of water and sand. The first step in separating the water and sand is to pour the mixture into the funnel. The water will be able to pass through the filter paper and it will be the filtrate. The sand will be unable to pass through the filter paper and will be left on the filter paper as residue.
Soluble Solids
Soluble solids are solids that dissolve in a liquid. We are able to separate a soluble salt from a solution in two different ways; evaporation and crystallisation. Both of these methods removed the solvent (the liquid) from an aqueous solution (which is a liquid with a soluble solid dissolved in the liquid). The methods for evaporation and crystallisation are very similar.
Evaporation
Evaporation is the quicker of the two methods. We set up the apparatus like what is shown below.
Soluble solids are solids that dissolve in a liquid. We are able to separate a soluble salt from a solution in two different ways; evaporation and crystallisation. Both of these methods removed the solvent (the liquid) from an aqueous solution (which is a liquid with a soluble solid dissolved in the liquid). The methods for evaporation and crystallisation are very similar.
Evaporation
Evaporation is the quicker of the two methods. We set up the apparatus like what is shown below.
We pour our mixture into the evaporating dish. We then slowly heat the solution using a Bunsen burner. The heating will cause the solvent (liquid) to start to evaporate, which will result in the solution becoming more concentrated; the solution becomes more concentrated because there is the same amount of the soluble solid (the salt) and less of the solvent as some of the solvent has evaporated. After some time of heating the mixture, crystals of the salt will start to form. We continue to heat the evaporating dish until we are left with dry crystals.
Crystallisation
If the soluble solid that we are separating from a mixture breaks down when it is heated, we need to use crystallisation instead of evaporation. Crystallisation is slower than evaporation.
The start of crystallisation is exactly the same as evaporation. We pour our mixture into an evaporating dish and gently heat the solution using a Bunsen burner. This will cause the solvent to evaporate. After some time, we will notice crystals starting to form in the solution; this is known as the point of crystallisation. When this happens, we remove the evaporating dish from the heat and leave the solution somewhere to cool. The salt will start to form larger crystals as the salt becomes insoluble in the cool more concentrated solution (the solution is now more concentrated because some of the solvent has evaporated). We then filter the crystals out of the solution, and leave the crystals in a warm place to dry (we filter the crystals by using the same method that was outlined at the start of this section). We can speed up the drying process by placing the crystals in a drying oven or a desiccator.
An example of crystallisation is the separating of copper sulfate from a copper sulfate solution.
Crystallisation
If the soluble solid that we are separating from a mixture breaks down when it is heated, we need to use crystallisation instead of evaporation. Crystallisation is slower than evaporation.
The start of crystallisation is exactly the same as evaporation. We pour our mixture into an evaporating dish and gently heat the solution using a Bunsen burner. This will cause the solvent to evaporate. After some time, we will notice crystals starting to form in the solution; this is known as the point of crystallisation. When this happens, we remove the evaporating dish from the heat and leave the solution somewhere to cool. The salt will start to form larger crystals as the salt becomes insoluble in the cool more concentrated solution (the solution is now more concentrated because some of the solvent has evaporated). We then filter the crystals out of the solution, and leave the crystals in a warm place to dry (we filter the crystals by using the same method that was outlined at the start of this section). We can speed up the drying process by placing the crystals in a drying oven or a desiccator.
An example of crystallisation is the separating of copper sulfate from a copper sulfate solution.
Separating Rock Salt
Rock salt is a mixture of salt and sand. The salt in rock salt is soluble (will dissolve in water) and the sand is insoluble (won’t dissolve in water). Here are the steps that we use to separate the sand and salt in rock salt.
We grind the rock salt up to make the salt crystals small so that the salt crystals dissolve well in water (the small salt crystals will have a greater surface area, which means that they will dissolve quicker/ more easily when we add them to water). We then add the grinded rock salt to water and stir to help the salt dissolve in the water. We now have a solution with the salt dissolved into the water, and the sand in the water but not dissolved in the water (the sand will not dissolve because sand is insoluble).
The next step is to filter the mixture, which we do by pouring the mixture through a funnel that is lined in filter paper. The water and the dissolved salt will pass through the filter paper, but the insoluble sand will not – the sand will be left on the filter paper (the sand will be the residue). We then collect the sand off of the filter paper.
The solution that has passed through the filter paper (the filtrate) is water with dissolved salt. We can separate the salt from the water by using evaporation. Evaporation will result in the water evaporating away, which will leave salt crystals. We could have also used crystallisation to separate the water and salt. (The salt in rock salt won’t break down or react when heat is applied, but if the salt did break down or react when heat is applied, we would have had to use crystallisation instead of evaporation).
We now have separated the sand and salt in rock salt.
Rock salt is a mixture of salt and sand. The salt in rock salt is soluble (will dissolve in water) and the sand is insoluble (won’t dissolve in water). Here are the steps that we use to separate the sand and salt in rock salt.
We grind the rock salt up to make the salt crystals small so that the salt crystals dissolve well in water (the small salt crystals will have a greater surface area, which means that they will dissolve quicker/ more easily when we add them to water). We then add the grinded rock salt to water and stir to help the salt dissolve in the water. We now have a solution with the salt dissolved into the water, and the sand in the water but not dissolved in the water (the sand will not dissolve because sand is insoluble).
The next step is to filter the mixture, which we do by pouring the mixture through a funnel that is lined in filter paper. The water and the dissolved salt will pass through the filter paper, but the insoluble sand will not – the sand will be left on the filter paper (the sand will be the residue). We then collect the sand off of the filter paper.
The solution that has passed through the filter paper (the filtrate) is water with dissolved salt. We can separate the salt from the water by using evaporation. Evaporation will result in the water evaporating away, which will leave salt crystals. We could have also used crystallisation to separate the water and salt. (The salt in rock salt won’t break down or react when heat is applied, but if the salt did break down or react when heat is applied, we would have had to use crystallisation instead of evaporation).
We now have separated the sand and salt in rock salt.
Use filtration to obtain the sand.
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Use evaporation to obtain the salt.
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