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Determining the relative atomic mass of Lithium

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Introduction

Chemistry Internal Assessment DCP and CE “Determining the relative atomic mass of Lithium” 2014 Raw data table: Measurement Mass (g) ±0.001 Volume -measuring cylinder (cm3) ±1 Temperature (°C ) ±0.25 Pressure(mbar) ±2 Mass of Lithium Trial 1 Trial 2 0.058 0.046 Volume of H2 produced when reacted with lithium Trial 1 Trial 2 97 79 Volume of distilled water 100 Temperature of room 20.00 Pressure of Room 1004 Observations: * Lithium was a shiny grey metal yet the outer surface of the lithium was darker than the inside. * When the Lithium was added to the water it began to fizz. Processed Data Table Measurement Mass (g) ±0.001 Volume -measuring cylinder (dm3) ±0.001 Temperature (K ) ±1 Pressure(kPa) ±0.2 Average Mass of Lithium 0.052 Average Volume of H2 produced when reacted with lithium 0.088 Volume of distilled water 0.1 Temperature of room 293 Pressure of Room 100.4 Equation of reaction 2Li + 2H2O → 2LiOH + H2 Literature Values Constant Value Source Ideal Gas Law Constant (R) ...read more.

Middle

This implies that the experiment was not significantly affected by systematic errors. Evaluation Limitation Explanation Effect on results Significance of Limitation Improvements Oil being left on the Li The lithium was kept in oil as lithium is very reactive and reacts with both water and air. So although we tried to remove the majority of the oil there was is the possibility of there still being some left on the lithium. This would have increased the mass of lithium thus would have increased our value for the relative atomic mass of lithium. This could have had a small effect as the oil would have increased our mass, yet we did manage to remove most of the oil. Dried the lithium more thoroughly, or use a larger piece of lithium which you could then use to dissect a 0.050g piece from the center, where it had not been in contact with oil. Presence of Lithium oxide Lithium oxidizes in oxygen so although the lithium was kept under oil when we removed it from the oil it would have begun to oxidize. ...read more.

Conclusion

This would have increased our recorded value of H2 and thus increased our value for the relative atomic mass of lithium. This is unlikely to have been very significant as the bubble was very small, thus would not have been a significant source of error. We could have improved our gas collection system by using a gas syringe as this is more accurate. Air in the tube Our method of gas collection involved using a rubber tube and a bung, there was gas in the tube plus and there was air displaced in the conical flask when placing the bung due to increasing pressure. This would have increased our recorded value of H2 and thus increased our value for the relative atomic mass of lithium. This could have significantly impacted the accuracy of our results, as the tubing would have contained a reasonable amount of gas. We could have improved our gas collection system by using a gas syringe, as this is more accurate. Only two repeats Due to time constraints we were only able to do two repeats of the experiment. Unknown reduced accuracy This makes our result less reliable. Do more repeats ...read more.

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