Determination of Relative Atomic Mass of Lithium

Determination of Relative Atomic Mass of Lithium

Evaluation:

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.

Limitations:

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;...

... middle of paper ...

...ll be clearer when the reaction is complete, thus more

concurrent results will be produced. Clearly there is also a need

for a control, although it was initially thought that it was very

obvious when the solution turns colourless, this practical has

shown that a control would be useful to compare the colours.

However the other problem of the solution returning to a slight

pink colour can be eliminated by waiting for this to occur, and

when it does, titrate it further opening the burette very

slightly, allowing acid to be added more slowly into the solution.

Carrying out titrations is a skill that develops with practice,

more repetitions will lead to improved results, both in accuracy

and precision.

Both methods are the most accurate, considering the equipment

available.