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DETERMINING THE MASS OF LITHIUM

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Introduction

DETERMINING THE MASS OF LITHIUM METHOD 1 RESULTS Mass of lithium used 0.12g Amount of hydrogen gas produced 182cm� TREATMENT OR RESULTS 2Li(s) + 2H2O(l) --> 2LiOH(aq) + H2(g) Moles of hydrogen gas collected Moles of H2 volume / 24000(cm�) 82 / 24000 0.007583333 moles Moles of H2 0.0076 moles Lithium that reacted H2 : Li 1 : 2 0.0076 : 2 � 0.0076 0.0076 : 0.0152 Moles of Li 0.0152 moles Relative atomic mass of lithium R.A.M mass / moles 0.12 / 0.0152 7.894736842 R.A.M of Li 7.8947 METHOD 2 RESULTS Titration of aqueous LiOH with 0.100 mol dm-3 HCl. Start (cm�) End (cm�) Titre (cm�) 0 34.90 34.90 0 34.80 34.80 0 34.90 34.90 Average result (34.80 + 34.90) / 2 = 69.7 / 2 = 34.85 TREATMENT OF RESULTS LiOH(aq) + HCl(aq) --> LiCl(aq) + H2O(l) Moles of HCl used in titration Moles of HCl concentration � (volume / 1000) 0.100 � (34.85 / 1000) 0.003485 moles Moles of HCl 0.0035 moles LiOH used in titration HCl : LiOH 1 : 1 0.0035 : 0.0035 Moles of LiOH 0.0035 moles Number of moles of LiOH present in 100cm� of solution from method 1 25cm� of LiOH is pipette each time. ...read more.

Middle

Also the oil lithium was dipped in was hard to remove completely. This could have also affected my result. It was also hard to put the stopper quickly on the conical flask, and this could have lead to some of the gas escaping, making the hydrogen gas produced to be less, affecting the end result. Although, this could not have caused a great inaccuracy in the result because it's due to human error. In both methods, there may have been errors in the cleanliness of the equipment as reagents from other experiment may have been present in the glassware, which can cause potential errors in the experiment. In method 2, taking the readings at eye level from the burette was not that accurate and the reading may have been in or out by 0.1 ERRORS IN MEASUREMENT When measuring out for the experiment, inaccuracy in measurement may have affected my final result. In method 2, when using the phenolphthalein, it's difficult to precisely use the same amount of drops when adding it to the LiOH. Lithium was measured using a 2decimal place scale. The measurement may have been precise, but since an oxide layer may have formed on the lithium, there may be some oxygen measured with the lithium, meaning that it's not the accurate mass of lithium used, thereby affecting the final result. ...read more.

Conclusion

and increase the volume of water, which will increase the amount of LiOH produced; therefore I will be able to do the titration more, and get more results which I can then compare and use the best one to get the best result for the experiment. Also, greater mass of lithium means there will be a smaller margin of error when measuring it out. I could have used a larger gas syringe perhaps a 200cm�. This will change the error margin from �1cm� to �0.5cm�, thereby increasing the accuracy of the experiment. I will also make sure that I use lithium from an inert atmosphere to prevent oxide layer forming, this will ensure that I'm only taking the mass of the lithium, and not the mass of lithium and the oxide layer. This will make my result more accurate. CONCLUSION From the evidence I have collected during this experiment, I have come to the conclusion that method 1 of finding the relative atomic mass of lithium is more reliable in comparison to method 2. This is because method 1 has the relative atomic mass which is close to the R.A.M of lithium, and more errors occur in method 2 than method 1. ?? ?? ?? ?? ...read more.

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