Safety Goggles and Gloves Tweezers
- First, I completely filled the 250 ml measuring cylinder with water (using the 50ml measuring cylinder).
- Then I filled the large bowl with water and placed the measuring cylinder inverted, making sure no water escaped from the cylinder.
- Then I carefully cut out a piece of lithium (using tweezers) and wiped it with a paper towel to remove the excess oil. Then I measured it on the pan balance making sure I had exactly 0.1 grams of lithium.
- I added excess water to the conical flask and placed the delivery tube under the inverted measuring cylinder.
- Finally, I gently added the lithium to the conical flask and placed he bung soon after.
- I observed the reaction taking place as the lithium fizzed and H2 replaced the water in the measuring cylinder.
- I then noted down the reading taken and repeated the expt. 5 times for accurate results (noting down my results in a table).
- With the results, I calculated the R.A.M of lithium.
Data Collection & Processing
Uncertainties
+- 0.01 grams (pan balance) – (0.01 / 0.1) * 100 = 10%
+- 2 cm3 (measuring cylinder) - (2 / 250) * 100 = 0.8%
Total Uncertainty = 10.8%
Processed Data
With this data, I was able to determine the R.A.M of Lithium.
(1 mole of gas occupies 24dm3 at room temperature and pressure)
- I used the average of all of the results.
230 + 192 + 235 + 186 + 208 = 1051 1051 / 5 = 210.2 cm3
- Moles = Volume / 24 dm3
Therefore → (210.2/1000) / 24 = 0.00876 moles of H2
-
2Li(s) + 2H2O(l) → 2LiOH(aq) + H2(g)
Since Lithium and Hydrogen are in a 2 : 1 ratio, we have to multiply the moles of H2 by 2 to get the moles of Lithium.
0.00876 * 2 = 0.01752 moles of Lithium
Now that I have the moles of lithium, I can work out the R.A.M.
Mr = Mass / Moles → 0.1 / 0.01752 = 5.71 Mr
Evaluation and Conclusion
The Literature value of R.AM for Lithium is 6.94 and from this experiment, I obtained 5.71. Although the experimental value is lower, it proves that the experiment overall, was good as the experimental R.A.M was not to different than the actual R.A.M (allowing for uncertainty’s and errors).
Possible source of error & Suggestions for Improvement
- Impure Lithium (oil coating).This allows the Lithium to react in the air which affects the mass. The experiment should have been done in an inert atmosphere to provide for more accuracy and should be done in the smallest amount of time possible.
- Some H2 escaped from the time when the lithium was placed in the conical flask, to when the bung was placed on it. This time delay caused inaccuracy. This probably caused the end result to be different and not accurate. For improvement, the lithium should have been suspended in the water with the bung in place by being tied to a string then released.
- The pan balance is not the most accurate piece of equipment to measure mass. This gave inaccurate results for the mass which in turn affected the final result.
- A measuring cylinder is not the most accurate piece of equipment to use to measure the amount of gas produced. A Gas jar should have been used to measure the volume of H2 produced, which is more accurate.
Safety and Precautions
There are many precautions to take in order to insure a fair and accurate experiment.
Gloves
Safety Goggles
Handle Lithium with tweezers
Wipe oil off Lithium
