Determination of Relative Atomic Mass of Lithium
In general the accuracy of the experiments was good. However with
practice, the accuracy could be improved; accuracy being how close the
results are to the real answer. I think I have carried pit the
experiment as well as I possibly could at the time with the given
conditions and time period allowed. I have gained precise results from
the practical. However, looking back at the analysis section, the
relative atomic mass values I found were not exactly 6.9 as presented
in the periodic timetable. Method (1) gave me 8.28; a difference of
1.38 and method (2) gave me 7.37, a difference of 0.43 to the
real/reference value. Therefore method (2) proved to be more accurate.
Overall the results were good and came close to the real values. There
were no anomalous results.
The main sources of error that I found to be evident and which were
out of my control were as follows:
* In method (1), due to the oil that lithium is stored in, not only
caused problems with weighing it, but also when I attempted to
quickly put pieces of lithium into the chonical flask with
distilled water, some pieces "stuck" on the weighing boat, sue to
residue oil having a "sticky" effect. This caused a delay in the
whole process and I was not able to place the bung in place
immediately, thus hydrogen was lost making the gas collected less
than what it was supposed to be.
* When weighing lithium the percentage error was:
(0.00005/0.00645) x 100= +or- 0.775%
Therefore the error possible caused by the weighing scales by default
is very low; less than 1%.
* In method (2), when carrying out the titrations, closing the tap
on the burette is a very vague process. When there is a colour
change in the solution, we are supposed to close the tap. However,
the colour does not change throughout the solution as soon as
there is a colour change. Therefore this will have caused in
concurrencies throughout, as the aim is NOT to put excess acid to
the solution titrated, the idea is to put the EXACT amount
required to neutralize the solution. I also found that the reacted
solution sometimes returned to a slight pink colour even after
turning completely colourless. Thus this caused inevitable error.
Accuracy and reliability:
In method (1) the procedure was very accurate; the equipment used is
very accurate, however as mentioned before, the gas lost when
replacing the bung caused a degree of inaccuracy. As shown by the
results, with the relative atomic mass found to be +1.38 over.
In method (2) not only were the results accurate but also precise. The
final relative atomic mass...