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The aim of this investigation is to determine the relative atomic mass of Lithium by two different methods:

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Introduction

The aim of this investigation is to determine the relative atomic mass of Lithium by two different methods: * By measuring the volume of Hydrogen produced when Lithium is dissolved in water; * And by titrating the Lithium Hydroxide produced. As a basic safety measure, goggles should be worn during the entire experiment and titration. It is important not to handle the Lithium with your bare hands. Lithium reacts violently with water, which may be present on your hands. When Lithium reacts with water it forms Lithium Hydroxide (LiOH) solution, which is corrosive - this means it can cause burns. You should transport the Lithium using tongs or by placing it inside a dry container. It is important not to spill the Hydrochloric Acid when handling it as it also corrosive and can cause burns. ...read more.

Middle

calculate the number of HCL used in the titration. ii) Deduce the number of moles of LiOH used in the titration. iii) Calculate the number of moles of LiOH present in 100cm� of the solution from the first reaction. iv) Use this result and the original mass of Lithium to calculate the relative atomic mass of Lithium. i) 0.1 moles of HCL in 1000ml 0.0001 moles of HCL in 1ml 0.003225 moles of HCL in 32.25ml ? 0.003225 moles of HCL used ii) This means I used 0.003225 moles of Lithium. iii) 0.003225 x 4 (as 25cm� was used) = 0.0129 iv) Relative Atomic Mass of Lithium: Mr = mass � moles = 0.10 � 0.0129 = 7.75 Evaluation The dissolving of the Lithium in distilled water was more accurate than the titration. But together the two reactions were quite accurate, gaining relative atomic masses of 7.50 and 7.75. ...read more.

Conclusion

Like oil, the area around the Lithium, which had reacted with air, is making the weighing and experiment inaccurate. The only way to overcome this problem is to prepare the Lithium and do the experiment in a vacuum. You could also carry out the preparation in a controlled inert environment. * When you are placing the bung in the conical flask. In order to add the Lithium to the water, you have to remove the bung, and replace it as quickly as possible when the Lithium is in the flask. This method allows some Hydrogen to escape if the bung is not immediately replaced. This error can be highly influential over the final accuracy of the experiment. The only way to overcome this problem is to develop a system that allows you to place the Lithium in the water without letting any of the Hydrogen escape. Possibly, a way of placing the Lithium in the conical flask without it touching the water, and then by knocking the flask you release the Lithium into the water. ...read more.

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