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Determining the relative atomic mass of lithium.

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Introduction

DETERMINING THE RELATIVE ATOMIC MASS OF LITHIUM BY JAVERIA MASUD 12-O Implementing Before I started my coursework I wrote a risk assessment which covered all the risks and hazards that might take place during the practical and how to avoid them. I know that lithium is a corrosive chemical and reacts vigorously with water to produce lithium hydroxide which is highly flammable. I made a list of all the chemicals and procedures that would take place during the experiment and which of them might affect my final result. To avoid hazards from taking place I wore eye protection at all times. I also wore a lab coat to protect any acid from spilling on my clothes. I did the experiment in 2 different parts. In the first one I produced lithium hydroxide. In the second one I did the titration of lithium hydroxide. From the first experiment, I reacted 0.09g of lithium with 100 cm� of distilled water to produce lithium hydroxide. As a result I collected 134 cm� of hydrogen gas. The table below shows the results produced for the second experiment that was the titration experiment. Volume 1 (cm�) Volume 2 (cm�) ...read more.

Middle

Now I will calculate the relative atomic mass of lithium again by using the results I got in experiment 2. LiOH (aq) + HCl (aq) ? LiCl (aq) + H2O (l) To calculate the number of moles of HCl that is hydrochloric acid, I would use the following formulae: Number of moles = concentration in mol dm(� ( Volume in dm� n = c ( V Concentration of HCl is 100 cm� = 0.100 dm� Volume is 27.0 cm� = 0.027 dm� n = 0.100 mol dm(� ( 0.027 dm� n = 0.0027 mols To deduce the number of moles of LiOH, I know that the mole ratio of HCl to LiOH from the equation is 1:1. Hence, Number of moles of LiOH = Number of moles of HCl n = 0.0027 mols The number of moles of LiOH in 25 cm� of a solution is 0.0027 mols. Hence, the number of moles of LiOH in 100 cm� of a solution can be calculated as follows: Number of moles of LiOH in 25 cm� = 0.0027 mols Number of moles of LiOH in 1 cm� = 0.0027 ( 25 n = 0.000108 mols ( Number of moles of LiOH in 100 cm� = 0.000108 ( 100 n = 0.0108 mols Using the results above from ...read more.

Conclusion

To minimise inbuilt uncertainties from the experiment, I could have used large quantities of chemicals as large quantities reduce the risk of percentage error. I could also have used equipment that had smaller divisions e.g. the measuring cylinder to decrease the percentage error. These uncertainties, if improved, could enhance the final result as there would be less risk of an error in the practical done and the final result might then be closer to the original relative atomic mass of lithium and the result produced would hence be more valid. A substitute method of calculating the relative atomic mass of an element accurately is by using the mass spectrometer. It is an instrument that measures the mass of atoms and molecules. The vaporised sample of an element being tested is introduced into the instrument and is then ionised by heating or is bombarded with electrons. The charged particles are then accelerated towards the electromagnetic field. The individual ions differ slightly in mass and charge. The lighter the ions or the greater the charge the on the ion, the greater will be the deflection. The ions are detected by means of a photographic plate. The ion detector then prints out a chart which is called a mass spectrum. Although, this is an improved method of calculating the relative atomic mass of elements, it is usually used in industrial chemical laboratories and not in educational institutions. ...read more.

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