Results
During the first reaction, I found that 160ml of Hydrogen was produced when placing exactly 0.1g of Lithium in 100cm³ of distilled water.
During the titration, I collected these results:
The average result that I will be using in the calculations is 32.25ml.
Calculations – first reaction
I will aim to;
- Calculate the number of moles of Hydrogen.
- Deduce the number of moles of Lithium.
- Calculate the relative atomic mass of Lithium.
i) 1 mole of Hydrogen = 24000cm³
0.00004167 moles of H2 = 1cm³
0.0066672 moles of H2 = 160cm³
Moles of Hydrogen = 0.0066672
ii) Moles of Lithium = 0.006666666672 x 2
= 0.0133344moldm-3
iii) Relative Atomic Mass of Lithium:
mr = mass ÷ moles = 0.10 ÷ 0.00133344 = 7.4994
Relative Atomic Mass of Lithium = 7.50
Calculations – Titration
I will aim to:
- calculate the number of HCL used in the titration.
- Deduce the number of moles of LiOH used in the titration.
- Calculate the number of moles of LiOH present in 100cm³ of the solution from the first reaction.
- Use this result and the original mass of Lithium to calculate the relative atomic mass of Lithium.
- 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
- This means I used 0.003225 moles of Lithium.
- 0.003225 x 4 (as 25cm³ was used) = 0.0129
- 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.
These results show that it is inevitable that inaccuracies can occur in the laboratory. In these experiments, inaccuracies could occur;
∙ When weighing the original mass of Lithium. Because Lithium reacts with the air, it is stored in jars of oil, to prevent any air getting to it. When the Lithium is weighed, you may be weighing a small amount of oil also, which obviously means you are not getting the exact amount of Lithium that you require. Although some of the oil is removed by the filter paper I used to carry the Lithium, it still means that the mass of Lithium is inaccurate. Therefore, it would be accurate if you could remove all of the oil. Oil is an organic material. A non-polar solvent could be used to remove the oil from the lithium.
∙ When the Lithium reacts with air. 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.