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NAME: NOR FATIHAH BINTI AHMAD
CLASS: M12H
TITLE: PRACTICAL 22: ANALYSIS OF THE IRON CONTENT IN IRON WOOL
BY
REDOX TITRATION
DATA COLLECTION
Qualitative:
1. Iron wool is grey in color.2. Potassium permanganate (VII)
solution, KMnO4(aq), is blue-black in color.3. 2M sulphuric acid
and 0.5M sulphuric acid are clear colorless solutions.4. When iron
wool is heated with 2M sulphuric acid, the clear colorless solution
gradually
turns grey.
5. At the end of heating, only small residue of iron wool is
left in 2M sulphuric acid.6. After filtering, the resulting iron
(II) sulphate solution, FeSO4(aq)is clear colorless
solution.
7. When FeSO4(aq) that is added with 0.5M sulphuric acid, is
titrated with KMnO4(aq), theclear solution gradually turns into
faint red in color.
Quantitative:
1) Mass of iron wool= 0.9958g 0.0001g
2) Volume of 2M sulphuric acid, H2SO4(aq)= 50ml 5ml
3) Volume of KMnO4(aq) usedTrial Volume of KMnO4(aq) used(
Start of experiment End of experiment
1 0ml 19ml2 20ml 37ml
3 37ml 55ml
4 56ml 72ml
5 73ml 99ml
Table 1: Volume of KMnO4(aq) used during start and end of
experiment
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9) Amount of iron in the iron wool=
x 100%
= x 100%
= 96.5%
10)Percentage error=
x 100%
=
x 100%= 0.52%
CONCLUSION
The theoretical value of iron content in iron wool is 96%,
whereas the experimental value
only exceeds 0.5% from the former value. Although the error is
not huge, there are still
limitations in the experiment that draws the line between the
book value and the empirical value.
EVALUATION
Limitations Suggestions
Overshooting during titration Produce a reference solution and
record the
volume of KMnO4needed to end up with such
result. For the subsequent trials, carefullytitrate KMnO4 drop
by drop when the reading
is approaching the one recorded for the
reference solution.
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From the experiment, the relative molecular mass(RMM) obtained
for amidosulphuric acid,
H3NSO3is 98.9, yet the calculation from book value points that
the supposed RMM for
amidosulphuric acid, H3NSO3 is 97.10. There is a difference of
1.8 between those two values and
as the calculation above indicates, 1.80% percentage error since
a few errors occurred during the
experiment.
Firstly, end point of neutralization might be exceeded. During
titration, overshoot might occur,
causing excessive amount of sodium hydroxide solution to be
titrated with amidosulphuric acid
solution. This can be prevented by starting the titration with a
trial experiment to obtain the right
end point the moment NaH2NSO3 suddenly turns yellowish orange .
When the end point has
been acquired, for the next few readings, make sure when the
volume of sodium hydroxide
solution in burette is approaching end point, titrate the
alkaline solution drop by drop. Besides,
the sample of NaH2NSO3 from the trial experiment can be kept
aside to be referred in the next
readings. On top of that, our eyes should focus on the reading
of sodium hydroxide solution in
burette to keep track of the end point.
Secondly, systematic error could have happened since there might
be foreign substances from
previous experiments inside burette and pipette. In order to
improve the accuracy of this
experiment, rinse burette with sodium hydroxide solution and
pipette with amidosulphuric acid
solution beforehand. The contaminants will be removed after
rinsing.
There are a few steps should be taken to minimize errors during
conducting experiment.
Start the experiment by weighing 2.5g of solid amidosulphuric
acid. The windows of electronic
balance must be tightly closed to prevent mass of air affecting
the readings later on. Ensure the
electronic balance is at 0.0000g before weighing by pressing the
tare button. Weigh the mass
of the container first, followed by the mass of container +
solid amidosulphuric acid. After that,
subtract the latter with former to obtain the mass of solid
amidosulphuric acid.
Next, while dissolving solid amidosulphuric acid, stir the
solution to increase the rate of reaction.
If the solid amidosulphuric acid cannot be dissolved after a few
moments, add more water and
keep stirring. Stop stirring when there is no more solute
left.
After amidosulphuric acid solution has been transferred into
volumetric flask, ensure our eyes
are on the meniscus level while making up the solution to the
250cm3
mark to avoid randomerror. If the meniscus level is exceeded,
the experiment has to be repeated all over again or the
solution has to be measured to 250cm3by using measuring
cylinder, hence increasing the
percentage uncertainty.
During the uptake of 25cm3
of amidosulphuric acid solution, do not hold the protruding part
of
pipette because the part is thinner and slight pressure from our
hand can break the pipette, thus
