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Chemistry reportAims/objectives of the experiment
The experiment was done in order to find out the amount of nickel in a solution using
titrimetric analysis, while also predicting the errors of equipment. it was expected that the
titration would give results that can be used to calculate the percentage of nickel in the
solution used.
Introduction
A previous experiment by Flaschka in 2013 in which a buffer pH 10 was used to make the
end colour change from yellow to violet, it was noticed that the end point was seen at a
sharper rate with the last few drops of EDTA changing the solution to orange and then
instantly to violet (Flaschka, 2013). Furthermore, it might be best to use an inert dye with
the indicator to make a colour change more visible, it is suggested that murexide be used
with methyl blue dye (Raheem and Prasad, 1993). Finally, for determining nickel it is best to
use excess EDTA and then back titrate using a standard cobalt solution, due to a lower error
rate and better suitability for such an experiment (Cameron and Gibson, 1961).
Methodology
Approximately 5 grams of the unknown nickel compound was weighed, and then placed
in a 250ml volumetric flask, using a funnel. Distilled water was used to flush the
compound through the funnel.
(gloves were used and goggles were worn to protect eyes and hands, this was because
the unknown salt that used is toxic via skin contact)
In order to fill the volumetric flask up to the marker, distilled water was added.
When the compound had fully dissolved, a 25ml sample was taken from it using a
pipette and pipette filler. This sample was then placed into a separate 250ml volumetric
flask.
using a measuring cylinder, 75ml of distilled water was measured out and added to the
sample. A separate measuring cylinder was then used to measure and add 10ml of 1 mol
of ammonium chloride to the sample. Finally, a very small amount of red murexide
indicator was added.
Distilled water was run through a burette to fill the tip, before 0.1 mol of EDTA solution
was used to fill it.
The starting point of the EDTA was noted before 10ml of EDTA was added to the sample
solution from the burette. The sample was swirled while this was done.
after the 10ml EDTA was added, a further 10ml of concentrated ammonia was added to
the sample. This was done in a fume cupboard to prevent inhalation of fumes from
ammonia or other damage it may cause.
EDTA was then continuously added dropwise to the solution until a reaction occurred
Once the end point was reached, the amount of EDTA remaining was recorded. Waste
was disposed of accordingly.
Steps 1 – 9 were repeated until 3 similar results were obtained and then mean was then
calculated.
, Results and discussion
During the experiment, 5 titrations were carried out in total and the final 3 were colsest in
value and therefore used to calculate the mean (see table 1). The first titration result was
expected to be an outlier as this was a “test run” and the endpoint was exceeded.
Table 1
titration start (ml) end (ml) vol EDTA used (ml)
1 10 29.1 19.1
2 10 29.2 19.2
3 10 28.6 18.6
4 10 28.7 18.7
5 10 28.7 18.7
mean 18.7
In each titration the start point was accurately measured to 10ml of EDTA in the burette as
this was a good way to keep track of results and made calculations easier. Furthermore, it
should be noted that errors in equipment (as seen in table 2) could have caused changes to
the values calculated during experiment. For example, in titration 1 the end point of EDTA
was 29.1ml so it was calculated that 19.1ml of EDTA was used to reach the end point, as
shown in table 1. For titration 2 it was found that 19.2ml of EDTA was used, and that 0.1ml
more EDTA was used than in the previous titration (see table 1 for all results), this could
have simply been human or equipment error (see table 2 for errors).
In titrations 1 and 2 , the colour changes were from yellow (when indicator was added) to
dark brown (when concentrated ammonia was added) to violet/purple (end point of
titration). In addition, it might have been better to use a buffer at Ph 10 to make colour
changes from yellow to the end point of violet as mentioned previously (Flaschka, 2013).
In contrast to the previous titrations, During the third titration it was noted that the colour
changes were different from the two previous titrations, instead they were from pale green
(when first 10ml of EDTA were added) to grey (when 10ml concentrated ammonia was
added) and then to violet/purple (end point of titration). The reason for this change in
colours was noted as there being a lack of indictor for the third titration which gave better
results. The difference in EDTA used for titration 3 and titration 2 was 0.6ml, this was more
than the differences noted in previous titrations, this could have been due to the change in
amount of indicator as noted, or equipment error (see above for values) in measurements.
In addition to the previous noting’s, During titration 4 it was noted that the colour changes
stayed the same as the previous titration done. This was the same for titration 5, and it was
calculated that titration 5 also had used 18.7ml of EDTA. After this, it was found that
titrations 3, 4 and 5 had the most similar results in order to calculate the mean (see above
for result). Although three similar results were obtained it may have been easier to then
back titrate using a standard cobalt solution along with the use of excess EDTA to make the
determination of nickel more accurate, as previously mentioned (Cameron and Gibson,
1961).
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