20A.4 Flashcards
what is heating under reflux and why do we use it
it is heating a reaction mixture within a flask fitted with a reflux condenser, and it is used to insure that volatile compounds that could escape when heating the reaction mixture stay within the reaction mixture since as soon as they leave they will go to the condenser and will be condensed back to continue reacting
how can a reaction mixture in a beaker be heated
by putting the in water or oil in a beaker that is being heated by a Bunsen burner or a electrical mantle
what helps the boiling mixture to boil smoothly
anti-bumping granules
how does a heating under reflux apparatus look like
page 272
what are the methods of separation
- simple distillation
- steam distillation
- fractional distillation
what is simple distillation used for
it is used to obtain a liquid product form a reaction mixture that has a boiling temperature much lower than the other substances in the reaction mixture
how does simple distillation work
an impure liquid will be heated in a flask connected to a condenser, the liquid with the lowest boiling temp evaporates first and passes into the condenser first, and so can be collected in the receiver separately from any other liquid that may evaporate later
what is the job of the thermometer in simple distillation
it is used to monitor the temp of the vapor as it passes into the condenser, if the temp remains constant for a while it indicated one compound is being distilled, if after a while the temp starts to increases it indicated a different compound is being distilled
what are the advantages of using simple distillation
advantage - easy to set up and easier to use
disadvantage - it doesn’t separated liquids as well as other separating techniques (like fractional distillation)
simple distillation should be used when the difference between the liquids in the mixture is
about 25c or more (and it should be a large diff)
how do you draw the apparatus of simple distillation
page 272 note make sure the thermometer is in line to the side arm linked to the condenser
what is stem distillation used for
it is used to separate an insoluble liquid from an aq solution.
how does steam distillation work
steam is passed into a reaction mixture involving an aq solution and a liquid that form a separate layer. the agitation of the liquid by the steam ensures that both the insoluble liquid and the aq solution are on the surface of the mixture and so can form part of a liquid that evaporates
what is the advantage of using steam distillation
the insoluble liquid is removed from the reaction mixture at a lower temp than its normal BP so less chance of decomposition
what liquid do we obtain using stem distillation
phenylamine - a liquid containing water and phenylamine distil at a lower temp than phenylamine can
how do you do draw steam distillation
page 273
what is fractionating column and its job
it is a column used in fractional distillation that is filled with glass beads or pieces of broken glass that act as surfaces on which the vapour can condense on and then be evaporated again once more hot vapour passes up the column, this makes the vapour experience several repeated distillations as it passes up the column providing better separation
when should fractional distillation be used
when the difference in boiling temp of the liquids in the mixture is small and when there are several compound in the mixture to be separated.
what is the advantages and disadvantages of fractional distillation
- provides better separation
- takes a long time (like me)
how do you draw fractional distillation
page 273
