Transcript http://www.sinc.sunysb.edu/Class/orgolab/hotfilt/hotfilt.ppt

HOT FILTRATION
Bantoo will show you how
to do the hot filtration step
in a crystallization
procedure.
First he has to show you
how to flute filter paper.
Scroll down.
FLUTED FILTER PAPER
Choose the size filter paper that will
just fit into the stemless funnel you
will be using.
Step #1: At all steps, crease
sharply. First, fold the paper in half.
Step #2: Fold in half again.
Step #3: Fold each quarter in half
again, with all creases facing up.
Here and in the next step, try to get
all the folds to meet at a sharp point.
FLUTED FILTER PAPER STEP #4
Fold each eighth in half again, but this time
make the folds in the opposite direction to the
one you have been doing.
HOT FILTRATION STEP #1
In an Erlenmeyer
flask, preheat the
solvent you will be
using for the
crystallization -don’t forget a
boiling stick or
stone.
Also set up and
preheat the
apparatus for hot
filtration: 2-3 mL of
the solvent in a
beaker (with
boiling stone),
stemless funnel,
and fluted filter
paper.
HOT FILTRATION STEP #2
A little at a time, add the
warm solvent to the solid
you are crystallizing.
Keep this mixture warm
too.
Stop adding solvent at
the point where no more
solid appears to be
dissolving and only
insoluble impurities
remain.
You can add 1-2 mL
solvent beyond this point
to compensate for the
evaporation which will
occur as you proceed.
HOT FILTRATION STEP #3
Filter the warm solution in
large portions.
At first you will probably need
to hold the filter paper down
with a spatula the way Bantoo
is doing here.
HOT FILTRATION STEP #4
After you filter the solution, look
carefully to see whether
crystals have formed in the filter
paper. This was the problem
here (the transparent crystals
don’t show up in the photo).
Wash these crystals through
with a small amount of the
warm solvent.
If you add more than a few
milliliters solvent at this step, in
most cases it would be a good
idea to evaporate some off
before you go on to the
crystallization cooling step.