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C1 I)Simple & Fractional Distillation
C1 I)Simple & Fractional Distillation
We can use simple distillation to separate a liquid from a solution. I am going to use simple distillation to separate water from sea water. We set the apparatus up like what is shown below.
We usually use a Bunsen burner to heat up the solution/ sea water. This will result in the substance with the lowest boiling point evaporating first; for the sea water example, the water will start to evaporate (change from a liquid to a gas). As the water evaporates, it rises up the flask and moves to the condenser. The condenser has cold water from a tap going in the bottom of the condenser and out of the top of the condenser. The condenser is cold, and it causes the vapor (the liquid that has evaporated and is now a gas) to condense and turn back into a liquid; for our sea water example, the water vapor will turn back into liquid water in the condenser. The liquid then runs on down to a collection beaker; for our sea water example, the beaker will contain pure distilled water. The rest of the solution will be left in the flask; for the sea water example, the salt will be left in the flask.
On the apparatus, we have a thermometer. We use this thermometer to ensure that the temperature of the flask is the correct temperature for the boiling point of the liquid in the solution.
On the apparatus, we have a thermometer. We use this thermometer to ensure that the temperature of the flask is the correct temperature for the boiling point of the liquid in the solution.
Fractional Distillation
We use fractional distillation to separate a mixture of liquids. A good example of where fractional distillation is used is to separate the different fractions in crude oil. The only difference in the setup for fractional distillation and simple distillation is that fractional distillation has a tall column filled with glass rods; the bottom of this column is hotter than the top of the column. The setup for fractional distillation is shown below.
We use fractional distillation to separate a mixture of liquids. A good example of where fractional distillation is used is to separate the different fractions in crude oil. The only difference in the setup for fractional distillation and simple distillation is that fractional distillation has a tall column filled with glass rods; the bottom of this column is hotter than the top of the column. The setup for fractional distillation is shown below.
The first step in fractional distillation is to place our mixture of liquids in the flask. All of the different liquids in the flask will have different boiling points. We heat the flask up gently until the thermometer at the top reads the temperature of the boiling point for the liquid that has the lowest boiling point (the lowest fraction). The liquid with the lowest boiling point will evaporate first. When the thermometer at the top reads the boiling point of the lowest fraction, the vapor of the lowest fraction will reach the top of the column. This vapor will then pass down the condenser where it will change from a gas to a liquid (condense) and run into a collection beaker.
Other liquids in the mixture with higher boiling points may also start to evaporate and rise up the column filled with glass rods. The top of the column is cooler than the bottom of the column. This results in the vapours of the higher boiling point liquids condensing part way up the column and running back down the glass rods in the column towards the flask. The column filled with glass rods ensures that only the fraction with the lowest boiling point (the fraction that we want) will rise up the column, through the condenser and into the collection beaker; it makes sure that we do not get any unwanted fractions.
After all of the liquid from the lowest fraction has been collected, we add more heat to increase the temperature to the boiling point for the second lowest fraction and change the beaker underneath the tube coming out of the condenser so that the next fraction goes into a separate beaker to the first fraction. We keep repeating this process until all of the fractions are in different beakers.
We always start with a low temperature and move onto the higher temperatures. This is because if we went from the highest to lowest temperature, the whole mixture of liquids would evaporate, rise up the column, down the condenser and into the collection beaker; if we did this, all of the crude oil would move from the flask to the collection beaker.
Other liquids in the mixture with higher boiling points may also start to evaporate and rise up the column filled with glass rods. The top of the column is cooler than the bottom of the column. This results in the vapours of the higher boiling point liquids condensing part way up the column and running back down the glass rods in the column towards the flask. The column filled with glass rods ensures that only the fraction with the lowest boiling point (the fraction that we want) will rise up the column, through the condenser and into the collection beaker; it makes sure that we do not get any unwanted fractions.
After all of the liquid from the lowest fraction has been collected, we add more heat to increase the temperature to the boiling point for the second lowest fraction and change the beaker underneath the tube coming out of the condenser so that the next fraction goes into a separate beaker to the first fraction. We keep repeating this process until all of the fractions are in different beakers.
We always start with a low temperature and move onto the higher temperatures. This is because if we went from the highest to lowest temperature, the whole mixture of liquids would evaporate, rise up the column, down the condenser and into the collection beaker; if we did this, all of the crude oil would move from the flask to the collection beaker.