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Determination of the relative atomic mass of Lithium.

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Introduction

Chemistry Coursework Determination of the relative atomic mass of Lithium In this experiment I am going to determine the relative atomic mass of lithium using two different methods, which are: * Measuring the volume of hydrogen produced * Titrating the lithium hydroxide produced Lithium is a group 1 alkaline metal. Method 1 - Procedure * Set up the apparatus as shown. The 250cm� conical flask contains exactly 100.0cm� of distilled water. * Weigh about 0.10g of lithium. Record the exact mass of lithium using an appropriate format. * Remove the stopper, add lithium and quickly replace the stopper. * Collect the gas evolved. Record the final volume. * Keep the solution in the conical flask form method 2. Results - I mole of gas occupies 24 000cm� at room temperature and pressure. 2Li(s) + 2H O(l) 2LiOH(aq) + H (g) � � Lithium - 0.130g Gas collected (hydrogen) - 186cm� Convert 186cm� into dm� = 186/1000 = 0.186dm� Number of moles of hydrogen = Mass/Ar = 0.186dm�/1000 = 0.0080 (to 1 significant figure). ...read more.

Middle

Therefore the number of moles of LiOH is the same as the number of moles of HCl, which is 0.00423M. Calculating the number of moles of LiOH present in 100cm� of the solution from Method 1 - Moles of LiOH = 0.00423 x 4 = 0.01692M = 1.692 x 10?� Calculating the relative atomic mass of lithium from the titration - Ar = Mass of lithium/ Mass of lithium hydroxide =0.130g/0.01692 =5.9101655 Atomic mass of lithium = 5.910 Evaluation - Overall, method 2, the titration is more accurate than the measuring of the hydrogen gas produced in method 1. The result I obtained in method 1 was 8.125 and in method 2 it was 5.910. Therefore the result I obtained from method 2, the titration was far more accurate than the result of method 1. Method 1 - The main source of error in method 1 was the collection of hydrogen gas. Whilst putting the bung on there was a loss of hydrogen gas. ...read more.

Conclusion

The titration is more reliable as there are no errors apart from the lithium coating and this occurred in both if the experiments. If I were to repeat the experiment I would make modifications to it to eliminate the main sources of inaccuracy that is the weighing and the collection of the hydrogen gas. Therefore using a syringe will eliminate the inaccuracy of the collection of the hydrogen gas. There is another problem of the hydrogen gas, which is that the actual gas might not be 100% hydrogen. But, that doesn't matter because all gases take up 24 dm� (1 mole) at room temperature and pressure. There is not a great deal of difference with this factor as it is not significant. The inaccuracy of the weighing scales cannot be eliminated, as there will always be a slight degree of inaccuracy but weighing the mass of lithium to a larger amount of significant figures can reduce this. Also, two different weighing scales could be used to make sure the same amount of lithium gave the same mass when weighed on two different scales. ...read more.

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