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14
CRER-1068
"APPENDIX 3
Determination of Calcium (1)
Weigh about 1 ge of the ash accurately into a 100 ml
platinum dish and ignite in a furnace for one hour at 800°C.
Allow to cool and add 20 ml of distilled water.
Cautiously
add 20 ml of 60% perchloric acid and 20 ml of40% hydrofluoric
acid. Heat on a hot plate inside a fumehood and continue
evaporation until dense white fumes of perchloric acid are
evolved.
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Allow to cool and add 10 ml of water and 20 ml of40%
hydrofluoric a¢id.
to dryness.
Repeat the fuming, evaporating almost
Allow to cool and dissolve the residue in 20 ml
of 1 M hydrochioric acid, with slight warming to facilitate
solution.
:
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- _
Transfer the solution to a 250 ml beaker; wash the dish with
a little water, adding the washings to the beaker.
Heat to
boiling on a hot plate to complete solution of difficulty
soluble material.
Allow to cool and filter through a Whatman No. 41 paper into
a 400 ml beaker.
Wash the precipitate and paper with several
portions of water, collecting the washings with the filtrate.
Discard the precipitate and dilute the filtrate to about
60 ml with water.
|
Add 40 ml of 8% oxalic acid and 10 ml of 50% ammonium
acetate solution.
Heat to about 80°C and neutralize with
4M ammonium hydroxide to pH 4.0, using bromocresol green
indicator (colour change of green to blue).
Stand the
beaker in a warm place for three to four hours.
Remove the supernatant liquid through a medium porosity
filter stick.
Dissolve the precipitate in 20 ml of 1N hydrochloric acid,
- dilute to 60 ml with water and repeat step No. 6.
Filter the solution through a tared, medium porosity,
sintered glass filter.
Wash the precipitate three times
with water and twice with methanol.
Dry the filter in an
oven at 110°C - 115°C to constant weight.
Weigh as Ca C204.H20
ge Ca/g ash =
0.274 x weight of CaCo04.H20
weight of ash
18 ake ee
10.