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Determination of the relative atomic mass of lithium

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Introduction

AS Assessed Practical Determination of the relative atomic mass of lithium Results - method 1 Mass of lithium used - 0.10g Volume of hydrogen evolved - 188.00cm Results - method 2 Rough Accurate 1 2 Initial volume reading (cm�) 0.00 0.00 0.00 Final volume reading (cm�) 34.69 34.98 38.94 Volume used (cm�) 34.69 34.98 38.94 Average volume of Hydrochloric Acid used = 34.98 + 34.94 / 2 = 34.96 cm Calculations - method 1 2Li + 2H2O 2LiOH +H2 2 moles 1 mole 1 mole of gas occupies 24000cm� at RTP Volume of H2 gas evolved = 188cm� 188 / 24000 = 0.0078 moles 0.0078 2 = 0.016 moles (2sf) Ar = 0.10 / 0.016 = 6.383 (3dp) ...read more.

Middle

The final result of the atomic mass is then affected by 5% which could have been 6.383 plus or minus 0.31915. * Another factor that could have affected the results is the time delay between putting the lithium in the solution and putting the bung on. Hydrogen could have escaped during this delay causing approximately a 1% error in the results. Therefore, altogether, procedure one could have a maximum of a 6% error within the results. Procedure 2 however is slightly more accurate because using a burette is much more accurate with only a possible 0.1cm error which is an approximate 0.28% error. This gives the procedure a possible total of 5.28% plus or minus of the final result. ...read more.

Conclusion

To overcome the delay in the time the lithium is put in the solution and the time the bung is put on the conical flask, a shelf like product could be attached already inside the conical flask so that the lithium could be placed on this and then simply shook off when you are ready to begin the experiment. This will prevent any hydrogen from escaping in the time it takes to put the bung on. To overcome the inaccuracy of weighing the lithium (apart from using a more accurate scales) a larger mass could be used for the experiment as this would produce a smaller percentage error because e.g. 5 % of 1.00g is far less than 5% of 0.1g. If all of these factors were changed, it would improve the overall accuracy of the experiment and the reliability of the results. Kimberley Davies 7410 AS Chemistry assessed practical 53621 ...read more.

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