Determination of the relative atomic mass of lithium

Method 1: procedure

1. Set up the apparatus as shown below. The 250cm3  conical flask must contain exactly 100 cm3 of distilled water.
2. Weigh between 0.08g and 0.13g of lithium. Record the exact mass of lithium using the measuring scale.
3. Remove the top of the flask, add the lithium and close it as quickly as possible to avoid H2 gas escaping.
4. The after that collect the gas and just record the final volumes of hydrogen using

Method 2: procedure for Titration

1. Pipette 25.0cm3 of the solution in the conical flask from method 1 into a clean 250cm3 conical flask and add 5 drops of phenolphthalein indicator.
2. Titrate with 0.100moldm-3 HCI(aq)
3. Record your results in an appropriate format in the space below.
4. Repeat the titration consistent result. Show all your result
5. Record the overall titre.

TABLES OF RESULTS& CALCULATINF THE RAM OF LITHIUM.

1. For volume

The average volume used of H2

Calculation of the number of moles of H2 that I have collected

Working out the number of moles of lithium that reacted in the experiment

 

Calculate the ram of lithium- (using my values above and the original mass of lithium)

         

2. FOR THE TITRATION

       

        

AVERAGE TITRATE

Number of moles of Hcl in a mass of 33.25 cm3

Number of LiOH in 100cm3 of the solution from method 1

Finding the original RAM of Lithium

                       

Possible hazard of the experiment- the possible hazards that can be encounter could be the reaction of the lithium with the lithium because it is really important that you mustn’t use too much lithium but to make sure that the amount of lithium used and the 100cm3 distilled water are somehow proportional.

Possible Errors in measurements- the main errors that I obtained where in my titration as I carried out 8 titrations and when it came to calculating I removed the most obvious anomalous results in my table to better improve my approximate RAM for the lithium. The errors that I felt were significant factors to titrations and my whole approximation of the RAM of Lithium.

Possible improvements to the methods & measurements- one of the major improvements that cold be done in the test could be the timing, because I think the time differences between when the phenolphalein makes the solution clear and the time I replaced the lithium in the conical flask and closed it might be the reasons way the test wasn’t as accurate as it could be.  

   One of the improvement I could suggest for the would be, to be more alert to when it comes to reading the results from the test tube and the timing of the phenolphalein in the titration could possibly be more accurate.

  Another possible improvement when to taking down the measurements is to make sure that my lithium stays constant because a minor different to 2 decimal places in my lithium calculation can produce anomalous results compared to the other results.

OVERALL OBSERVATION FROM MY RESULTS AND CALCULATION

    Looking back at my results I can see it looks fairly accurate with not a lot of anomalous results. From the relative atomic mass I obtained from method1: measuring the volume of hydrogen gas given, and Method2 titrating the LiOH, I can see that the RAM obtained from the Method 1 gives more accurate and approximate RAM of Lithium.

From method was 6.5g and method 2 was 7.5g but the actual RAM of Li is 6.9g, so I would say that method seems to be more accurate.  For method 2 on average the 25cm3 of LiOH I was using required  0.003325cm3 of 0.100mol dm-3 of HCl.

Implementation and analysis.

 When following the procedure for both methods (volume and titration) you have to make sure that safety precaution like wearing goggles and gloves are followed carefully. Also if you have a long hair, you will need to tie it back to avoid contact with chemicals. All the safety precaution should be followed carefully as working with acids and other reactive elements can be dangerous (in this case especially lithium as it can react with the skin due to the skins moisture and also it can react with the atmosphere, so it is better to keep it in oil). Therefore it is very important to follow these precautions and take extra care when doing the experiment in order to protect yourself and others working around you.

During and after the experiment, you need to record your results in a table of results. However when calculating the ram of li using your results you need to use the average of the volume of hydrogen gas used (for the volume)  

and the average of the volume of the HCI used (for titration).

When calculating the ram of li using the results from the titration, the first result for the HCI titrated for each set needed to get rid off. Therefore I did four experiments for the volume of hydrogen gas used the first method for the volume;I got 8 results for the titration method.

However for the calculations for the titration method to be more accurate, I had to get rid of some the results that seemed to be the first result of each set, as they are usually just a rough estimate. In this case I had to discard the 1st and 4th try, and then I found the ram of li using the average of the other 4 results (meaning the 2nd 3rd 5th and 6th try).  My overall conclusion for the analysis for both the experiments is that both tests worked out well and I think that both experiments I seemed to get a very close approximation to the actual mass of lithium and this probably means that my lithium measurements were accurate enough and that the procedures must have accurate enough but I think I could have achieved a better approximation if I was able to carryout the test in one day and in the same in environment meaning temperature isn’t becoming a factor to my experiment.

EVALUATION

The improvement I think could be made to the experiment are :

• I think I could have used a lower mass of the lithium I used.  I also think that the weight of the lithium was crooked because removing the oil the lithium was stored in was hard and I also think that some of the mass of the oil was contributing to the overall mass.
•    I think there also could have been some impurities with my lithium mass because it could be possible that it might have reacted with the air (forming a layer of LiO2 on top of the pure lithium) or it could also be that the measuring scale gave me the wrong measurement, and I could have improved by using a more accurate scale.
• There could also have been some improved on collecting the H2, because I think there could have been error in timing in stopping the timer in between when collecting the H2 in the conical flask and when adding the lithium ad closing the top, but I think this would be a minor contribution to the overall inaccuracy of the experiment.
• Room temperature could have also contributed to the overall inaccuracy of the experiment as I did the test different days.
• I think I could have used a more accurate apparatus to measure the 100cm3 of distilled water I used thus improving the approximation RAM of the lithium.

                     I think I could have minimised and possibly reduced the errors that could have made this experiment  
            inaccurate by:

• Removing the oil from the lithium by other means instead of wiping it off with a tissue, perhaps it would best if I used some type of non-polar solvents (e.g. pure alcohol) to prevent a reaction occurring when I am removing the oil.
•   Perhaps it could be possible to use more accurate scale to reduce my error.
• Reducing the time lag when replacing the top on the conical flask after placing the lithium init.

from both tests I found that my method 1 –collecting the volume of the H2  gave a more accurate and a close approximation of the RAM of lithium. This one seemed to have more accurate approximation then my method 2 for carrying out the titration and I think one of the reasons why method 2 was as accurate as method 1 was because of my timing and the lack of constancy in the test.

I think that the experimental procedure was suitable in both experiments even though I prefer the finding the volume instead of using titration, and when it came to anomalous results I felt that I was obtains a lot more results appeared in the titration procedure this is because I did 8 tries and selected the results that I felt didn’t have a lot of difference between and I ignored the ones I thought were anomalous to the rest. The reasons for any improper results that I obtained were I think due to the weighing of my lithium or perhaps any impurities that could have formed with the duration of the experiment.

     I felt that there were several limitation not only within my procedure or calculation but also within my weighing of the lithium because I felt that measuring scale seemed to be giving me irregular sizes even though the measurement seemed to be close however this could be due to the fact that the measuring scale wasn’t functioning as well as it could have and I think I should have used a much newer measuring scale and this would probably have made my measurements more accurate and thus get a closer approximation of the mass of lithium. I think that my overall accuracy in both experiment was very accurate as I got a close approximate figure of the mass of the lithium from my calculation, and any limitation that could have prevented me from getting the actual mass of lithium would be that perhaps that of human errors mainly down to me and the state of my measuring equipments. Any improvements that I could suggest for the experiments limitation is to carry out the whole experiment in one day because this will ensure that equipments are constant carry out the experiment using better equipments.  I think that my main sources of error and the limitation in both experiments were partly due to faulty in equipments and human errors. Any modification if I could do the test again is to change the equipments I used and try to complete the experiment quickly in order to minimise any human errors.