GRAVIMETRIC DETERMINATION of NICKEL
Solutions:
HCl (1: 1), HN0 3 (1:1), NH 3 sol. (conc.), 1 % DMG in ethanol, 30% ethanol:
Things to be done before the experiment:
Wash sintered-glass filter crucible with 6N HN0 3, and then distilled water. Dry it
to a constant weight of 0.3-0.4 mg.
Procedure:
1) Take your unknown solution and dilute to the mark.
2) Pipette 25 ml of the dilute unknown solution containing the nickel salt into a
400 ml beaker provided with a watch-glass cover and stirring rod.
3) Add 5ml of dilute HCl (1:1) and dilute to 200 ml with distilled water.
4) Heat the beaker on hot plate to about 70-80 oC.Do not boil.
5)Add 30 ml 1% DMG solution dropwise from the burette with good stirring.
Immediately add ammonia solution dropwise, directly to the solution, not down
the side of the beaker, with constant stirring until precipitation takes place, and
then in slight excess. It is important that the solution should be distinctly
alkaline at this point.
6) Cover the beakers with watch glass and digest for about 20-30 minutes on a
hot plate. Allow the precipitate to stand for 30 minutes, cooling at the same
time.
7) Filter the cold solution through a sintered –glass crucible, previously heated
to 110-120 oC and weighed after cooling in a desicator. Wash the precipitate
with cold water to remove Cl - at least 3 or 4 times. Finally, wash the precipitate
once with 30 % alcohol to remove excess DMG.
8) Dry it in the oven for 30 minutes. Allow to cool in a desicator for 20 minutes
and weigh. Dry to constant weight. Repeat the same overall process to
constant weight of 0,3-0,4 mg.
DATA
Trial 1
Sintered glass crucible (empty)
Avg.wt. of crucible (empty)
Sintered glass crucible + sample
Trial 2
Trial 3
_______g _______g _______g
____________________g
_______g _______g _______g
Avg. wt. of crucible + sample
____________________g
Avg. wt. of sample as Ni(DMG)2
____________________g
Molarity of unknown Ni solution
_____________________