Distillation Flashcards
What is simple distillation used for?
It is used for separating out a liquid from a solution.
How can you get pure water from seawater, using simple distillation?
1) Pour your sample of seawater into the distillation flask.
2) Set up the apparatus as shown in the diagram. Connect the bottom end of the condenser to a cold tap using rubber tubing. Run cold water through the condenser to keep it cool.
3) Gradually heat the distillation flask. The part of the solution that has the lowest boiling point will evaporate - in this case, that’s the water.
4) The water vapour passes into the condenser where it cools and condenses (turns back into a liquid).
5) Eventually you’ll end up with just the salt left int the flask.
What is the problem with simple distillation?
You can only use it to separate things with very different boiling points.
What can be used to separate a mixture of liquids with similar boiling points?
Fractional distillation.
Describe the fractional distillation of crude oil?
1) Put your mixture in a flask. Attach a fractionating column and condenser above the flask as shown.
2) Gradually heat the flask. The different liquids will all have different boiling points - so they will evaporate at different temperatures.
3) The liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column.
4) Liquids with higher boiling points might also start to evaporate. But the column is cooler towards the top, so they will only get part of the way up before condensing and running back down towards the flask.
When the first liquid has been collected, raise the temperature until the next one reaches the top.
