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8/18/2019 Back Titration of Ammonia
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Title: Back Titration of Ammonia
Aim: To determine the percentage of ammonia in an ammonium salt providedusing a back titration.
Apparatus: Three 250 cm3 conical asks, 25 cm3 pipette, to 200 cm3 beakers,
one !00cm3 beaker, one 250 cm3 beaker, "lter funnel, safet# goggles, 50 cm3 burette, red litmus paper, burner, tongs, pipette "ller
Materials: screened meth#l red indicator, 0.!$ ammonium chloride solution, 0.!$sodium h#dro%ide solution, 0.! $ h#drochloric acid solution, distilled ater
Procedure& All glassare ere thoroughl# ashed cleaned. A 25 cm3 pipette asthen rinsed tice ith a small amount of ammonium chloride solution. 25 cm3 of
ammonium chloride as then pipetted into three 250cm3 conical asks each. 50
cm3 of 'a() as then pipetted into each conical ask, and then placed on burner
to boil. (nce the solution in the ask began to boil, and it as noted that the
solution volume decreased* distilled ater as added. The vapour escaping the
ask as checked intermittentl# ith a strip of red litmus paper until the vapour no
longer turned a strip of red litmus blue. The ask as then removed from the heat
and as placed under a running stream of ater to cool.
(nce cooled, 3 drops of meth#l red ere added to the ask, observations ere
noted.
A hite tile as placed on the base of the burette stand beneath the burette. The
"rst ask as placed on the hite tile and the solution in it graduall# titrated ith
)+l from the burette. The burette tap as turned o from time to time to allo
solution on the side of the burette to drain don to the solution. 'ear the end point
the titration as carried out more slol#, then drop b# drop until a single drop from
the burette caused a permanent colour change. The volume of )+l used as
recorded in the table as "nal volume for the trial titration.
The volume of )+l in the burette as replenished and the other to back titrations
carried out, this time more rapidl#, until a volume of about 2.00 cm3 less than the
volume used in the rough titration as run into the titration ask, the tap turned o
and then on to slol# add the )+l to the ask then drop b# drop until the end point
as reached. The initial and "nal volumes of )+l used for each titration as
recorded in the table.
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