simple and fractional distillation Flashcards
what is simple distillation
If we want to keep the liquid during crystallisation we use distillation. Simple distillation is used to separate a liquid from a solid if we want to keep the liquid
what is fractional distillation
Fractional distillation allows us to separate two different liquids inn a mixture (of different boiling points)
how does simple distillation work
1) We place our solution with the liquid and in a flask that is connected to a continuous glass tube. The glass tube is surrounded by a jacket which we call the condenser
2) Cold water from the tap continuously runs through the condensers. This keeps the eternal glass tube cold. After running through the condenser the water simply goes down the sink.
3) We also have a thermometer as part the apparatus
How does it work
1) We start as heating the solution in the flask by using a Bunsen burner
2) The liquid starts to evaporate and turns into a vapour. The vapour rises up the glass tube. The thermometer show us thee temp is rising
3) The vapour passes into the condenser. The condenser is kept cold as we are circulating cold water around it. This means the vapour now condenses turning into a liquid as it passes through
4) We can collect the liquid in a beaker. So, at the end, we should have crystals of our solid in the flask and our liquid in the beaker
uses of simple distillation
simple distillation can be used to produce water from sea water. However a great deal of energy is used during distillation so other techniques are used instead.
how does fractional distillation work
In the flask containing the mixture is attached to a long column containing beads. (this is called the fractionating column)
1) We start by gently heating our mixture. Both of our liquids will start t evaporate. The one with the lower boiling point will evaporate more easily. We now have a mixture of two different vapours making its way through the fractionating column
2) When the vapours hit the fractionating column they condense and drip back down back into the flask where the liquids evaporates again.
3) Repeated evaporation and condensation increases the amount of the lower boiling point chemical (liquid) in the fractionating column. The lower boiling point chemical makes its way up the fractionating column ahead of the higher boiling point chemical.
4) As the vapour pass up the column, they reach the thermometer. The temp of the thermometer begins to rise. This means a mixture of two different vapours are passing over the thermometer. The mixture will contain a larger amount of the lower boiling point chemical.
5) These vapours pass into the condenser and turn into a liquid. This is still a mixture of two chemicals which we can collect.
6) There comes a point where the temp of the thermometer reaches the boiling point of the first chemical and it will stop rising.
7) At this point we have mainly one chemical passing into the condenser. This condenses and we can collect it in a fresh beaker. This is our first proper fraction
8) After a while the temp will start to rise again. Once again a mixture of vapours are passing through the condenser but this time it is primarily contains the vapour with the higher boiling point.
9) Once the temp becomes constant, we know we are collecting a relatively pure sample of the second chemical
10) we have now separated two chemicals based on their boiling points
what factors must we consider when we are separating t two chemicals using fractional distillation
Factors we need to consider
1)If the two liquids have a similar boiling points, then it is much harder to separate them. We might need to carry out several rounds of fractional distillation
2) The equipment used in this particular experiment is not specifically useful when separating large volumes of liquid
e. g. when we refine crude oil in this case we would carry out fractional distillation in a different way but the same principle remains the same
