= 0.01 mol (2dp)
I have used this equation as it indicates that if a gas is kept at equal volumes in the same conditions it contains the same number of molecules.
- The number of moles of lithium:
The equation above suggests that there is a 2 : 1 ratio. This means that for every (1) mole of hydrogen there are (2) moles of lithium. Therefore the number of moles of lithium needs to be doubled.
2 x 0.00641667 = 0.0128333 mol
= 0.01 mol (2dp)
- Using these values and the original mass of lithium the relative atomic mass is:
Relative Atomic Mass = Mass / Moles of lithium
= 0.10 / 0.0128333
= 7.792207792
= 7.8 (1dp)
This reveals that the way that I conducted procedure (1) was accurate as the relative atomic mass found is similar to the average mass shown on the periodic table, 6.9. It is important that my answer lies between the range of 6.9 and 7.9 otherwise it will bare the relative atomic mass of another element.
I have written my answers to (2) decimal places initially as some calculation gave me answers such as (0.0) when I wrote them to (1) decimal place. This means that they would have been mathematically incorrect. However my final relative atomic mass of lithium has been written to (1) decimal place, as the measuring cylinder that I used did not have accurate intervals. I have used the complete numbers in my calculations so that my final results will be to a high degree of accuracy.
Procedure (2):
I have conducted this experiment four times so that any anomalous result will be noticed and subsequently I will not use it in my final calculations. This has occurred in the case of experiment (2). Therefore in my calculations for the average, I will not use this result.
Average = 31.6 + 31.6 + 31.5
3
= 94.7
3
= 31.5667 cm³
= 31.57 cm³ (2dp)
- The number of moles of HCl used in titration:
No. of moles = concentration x volume
1000
= 0.100 x 31.57
1000
= 0.0315667
= 0.03 mol (2dp)
The equation above suggests that there is a 1 : 1 ratio. This means that for every (1) mole of lithium hydroxide there is (1) mole of hydrochloric acid used. Therefore the number of mole of lithium hydroxide and hydrochloric acid will be the same. The number of moles of lithium hydroxide used will be 0.03 mol (2dp).
- The number of moles of LiOH present in 100cm³ of the solution:
In procedure (1) I used 25 cm³ of the solution; this indicates that I will have to multiply my answer above by (4) to reach 100cm³.
= 0.0315667 x 4 = 0.1262667 mol
= 0.13 mol (2dp)
- Using these values and the original mass of lithium the relative atomic mass is:
Relative Atomic Mass = Mass / Moles of lithium
= 0.10 / 0.1262667
= 7.91974648
= 7.92 (2dp)
In this procedure all my answers have been written to (2) decimal places as the equipment I used was more accurate and had a higher degree of accuracy.
From these results I can draw the conclusion that lithium has a relative atomic mass of 7.8 and 7.9. Although the periodic table suggests that lithium has a relative at9omic mass of 6.9 I believe that different masses of lithium will have a difference in relative atomic mass.
