Purification of Potash Alum by Crystallization Video Lecture - Class 11

purification of pettish island by
crystallization potage alum is a double
salt of potassium sulfate in aluminium
sulfate we can make pure crystals of
potash alum by the process called
crystallization in this process crystals
of the pure substance are formed by
cooling a hot saturated solution of an
impure sample the different steps
involved in the crystallization process
our preparation of solution of the
impure sample filtration of the solution
concentration of the filtrate cooling
the concentrated solution separation and
drying of crystals our aim is to prepare
crystals of pure potassium from the
crude sample materials required crude
sample of potash alum distilled water
ethyl alcohol water mixture 250 ml
beaker x' china dish glass rod spatula
funnel filter papers watch gloss test
tube evaporating dish trough stand with
clamp wire gauze tripod stand Bunsen
burner and sand bath procedure
preparation of solution of the impure
sample take about 30 ml of distilled
water in a beaker to this add about 6
grams of the crude sample of potage alum
using the spatula stir the contents of
the beaker with a glass rod to make the
solution clear warm to dissolve the
whole of alum present in the solution
filtration of the solution clamp the
funnel in which a filter paper is fixed
to the stand
place the China dish under the funnel
the SEM of the funnel should touch the
wall of the China dish to avoid the
solution splashing out pour the solution
into the funnel over the glass rod and
collect the filtrate in the China dish
the insoluble impurities are left on the
filter paper concentration off the
filtrate heat the China dish in a sand
bath till the solution is reduced to
about one third of its original volume
to avoid crust formation on the sides of
the dish stir the solution continuously
with the glass rod to know if the
solution has reached its crystallization
point remove a drop of the solution at
the end of the glass rod and cool it by
blowing the appearance of a crust or
tiny crystals on the glass rod shows
that the crystallization point has been
reached transfer the hot saturated
solution into the evaporating dish
cooling the concentrated solution place
the evaporating dish containing hot
saturated solution in a trough
containing water cover the dish with the
watch glass and allow it to cool slowly
for some time as the solution cools
colorless crystals of potash alum begin
to separate and the crystallization will
be completed after half an hour
separation and drying of crystals decant
the mother liquid carefully into a
beaker wash the crystals three or four
times with a little ethyl alcohol
containing a small amount of cold water
place the crystals and a filter paper
which soaks up the solution transfer the
crystals to another filter paper and dry
them by pressing gently between the
folds of the filter paper now transfer
the crystals into a dry test tube the
crystals of Hitoshi Alma colorless and
transparent precautions the filtrate
should be evaporated slowly by gently
heating during concentration the
filtrate should never be heated to
dryness the solution should be cooled
slowly without disturbing it