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Determination Of The Atomic mass of Lithium.

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Introduction

Chemistry Coursework-Determination Of The Atomic mass of Lithium I am going to determine the relative atomic mass of lithium by two different methods: * Method 1: I will measure the volume of hydrogen produced when a known mass of lithium reacts with water. * Method 2: I will titrate the solution of lithium hydroxide produced. Results from method 1: 0.13g of lithium reacted with 100cm3 of water to produce 238cm3 of hydrogen gas. As I know that 1 mole of hydrogen gas occupies 24dm3. * Calculate the number of moles of hydrogen that I collected. 238/24000 = 9.916*10-3 To check this I will use the formula below. V=nRT * Deduce the number of moles of lithium that reacted. The ratio of lithium to hydrogen is 2:1 so the moles of hydrogen have to be multiplied by 2 to get the correct answer. 0.009916666*2 = 0.019833333 moles * Using the values from above and the original mass of lithium, calculate the relative atomic mass of lithium. Moles = Mass Ar Ar = Mass Moles Ar = 0.13 0.0198333 Ar = 7.090914248 Results from method 2: * Titration of aqueous lithium hydroxide with 0.100 mol dm3 Hydrochloric acid. ...read more.

Middle

* Firstly I will analyse where I think that errors which would have affected my result in method 1: o The bung had to be secured over the conical fast quickly but it's almost impossible to do this without losing any hydrogen. o The tube had to be in the measuring cylinder. (This wasn't an error which would affect your results, just ruin your experiment as no hydrogen would be collected). o When you placed the measuring cylinder in the trough, the water line had to be at a mark on the scale so you could accurately determine the end volume of hydrogen produced with accuracy. o Lithium had to be weighed using appropriate scales. o Tube had to be checked to see if there were any holes or leakages so no hydrogen would be lost. o Impurities may be present in the lithium distorting the results slightly. (if there is any impurities it would only be very small amounts) o All traces of oil may not be removed from the lithium before it is reacted with the water. o The age of the lithium may be a cause for slight error in the results as older lithium may have a thicker layer of metal oxide around it. ...read more.

Conclusion

o Use the equipment as best you can measure the solution carefully to ensure accuracy. o Ensure the acid is mixed correctly to produce the exact concentration needed. * Now I will explain which experiment was more accurate and why I think this is the case. o There is one point that has to be remembered. The second experiment contains the errors that I have made in the first experiment, any errors from the first experiment are carried over making the titration experiment seem a lot more inaccurate, and this is shown by the results that I have obtained. Also the fact that there are three titration experiments making three results and I used the average of these this backs up the fact that the second method is less accurate. o The first experiment shows a far more accurate result than the second, I think this is due to the fact that as you can see from the section above I have found a lot more ways to make the first experiment more accurate, plus o Also as we are only in a school lab the precision of the equipment cannot be of an exact standard, in the two methods you have to measure out volumes of solutions so again slight errors will occur. ...read more.

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