- Remove the stopper from the conical flask, place the lithium in the conical flask and immediately replace the stopper to ensure no hydrogen gas escapes.
- Collect the hydrogen gas in the measuring cylinder and record the final volume.
Results
Calculations
1st Attempt -
76 cm 0.00317 0.00317 X 2 =0.0063
24000 cm
0.044 6.98
0.0063
2nd Attempt –
78 cm 0.00325 0.00325 X 2 = 0.0065
24000 cm
0.042 6.462
0.0065
Average Titre –
77 cm 0.00321 0.00321 X 2 = 0.0065
24000 cm
0.043 6.154
0.0065
Part 2
LiOH (aq) + HCl (aq) LiCl (aq) + H2O (l)
Equipment
25.00 cm Pipette
Lithium Hydroxide Solution
250 cm Conical Flask
Hydrochloric Acid
Burette
Phenolphthalein Indicator
Standing Clamp
Method
- Use a pipette to accurately measure 25.00 cm of the solution of lithium hydroxide. Place it into a 250 cm conical flask and add 5 drops of phenolphthalein indicator.
- Set up the apparatus accordingly (as shown below).
- Titrate this with 0.100 mol dm of hydrochloric acid.
- Accurately record your results.
- Repeat the titration a number of times and record the average titre.
Results
1st Attempt
Calculations
Average Titre -
15.35 X 0.1 = 0.001535
1000
0.001535 X 4 = 0.00614
0.042 = 6.84
0.00614
2nd Attempt
Calculations
Average Titre –
15.20 X 0.1 = 0.00152
1000
0.00152 X 4 = 0.00608
0.044 = 7.24
0.00608
Analysis
Overall I believe my experiment was accurate and that I carried out a fair test apart from a few minor errors, looking at my results you can identify this. The results do show slight error, as on the first attempt the amount of hydrogen gas collected in the measuring cylinder was 50 cm . Then the second and third attempt attempts gave the readings 76 cm and 78 cm . This must mean there was an error in the procedure of the experiment.
The titres were also quite accurate as the results were within 0.10 cm of each other. For the first attempt the result was 15.30 cm and 15.40 cm , and the results from the second attempt were both 15.20 cm . Although both attempts were accurate, there was also a rough titration of 15.00 cm , in which indicates that there were slight errors in the overall experiment.
From analysing my results I found that the second method I used was more reliable compared to the first method, as when using 0.040g of lithium in the first method it gave a relative atomic mass of 6.614. When using 0.042g of lithium in the second method it gave a relative atomic mass of 6.84. This gives evidence to believe that the second method is more consistent as its relative atomic mass is closest to 6.941, in which I found is the relative atomic mass of lithium.
When looking at the second method I found that the best weight of lithium to use for the experiment is 0.042g as when using this it gave a relative atomic mass of 6.84. In comparison when using 0.044g of lithium it gave the relative atomic mass of 7.24.
In concern of method 1 I found that there was a difference in the results of the two different volumes. The most accurate reading of the volume of hydrogen gas was 76 cm as it gave a relative atomic mass of 6.98, where as 78 cm gave a relative atomic mass of 6.46.
Evaluation
As you can see from the results looking at the rough titration, you can identify there were slight errors. The errors may have occurred in the procedure of the experiment, as first of all there were a few variables that could not be controlled such as the temperature was approximately 25 C and the pressure was standard. Another area where errors may have occurred is whilst cutting a sample of lithium. Errors may have occurred here because it is impossible to obtain a 100% pure sample of lithium. This is because lithium is stored under oil to minimise oxidation taking place by oxygen, water and carbon dioxide in the air. There may have been an error when cutting the lithium sample and then when attempting to clean the oxidation residue off the lithium. There also may have been errors in the cleanliness of the equipment as reagents from other experiments may have been present in the glassware, this can cause potential errors in the experiment as it influences the incorrect results. This also applies to the measurement of the reagents I took, the measurement of lithium using the measuring scales and also accurately reading the results from the burette. This leaves error for concern, as it cannot always be entirely accurate.
One factor in which I believe probably gave me some incorrect results was the impossible task of insuring all the hydrogen gas is collected in the measuring cylinder, as whilst carrying out the experiment you come to a time when you must remove the stopper from the conical flask and place the sample of lithium in the conical flask, at the same time as replacing the stopper. This allows some hydrogen gas to escape from the conical flask into the atmosphere making it impossible for the experiment to be completely accurate.
From the evidence I have collected during this experiment I have come to the conclusion that the second method of finding the relative atomic mass of lithium is more reliable in comparison to the first method. I believe this for many reasons, firstly the relative atomic mass of the second method is closest to 6.941. I also believe that the assemblance of the apparatus is more difficult in the first method compared to the second method of titration.
There are a number of improvements that could have been made as to make the experiment a fair test. Firstly, whilst carrying out the experiment there were a few minor set backs such as in the first method an inverted measuring cylinder was not available and so I may have recorded the results incorrectly.
Health and Safety
There are many safety precautions you must carry out in order to ensure the experiment is a fair test and to ensure the safety of yourself and others around you when carrying out this experiment. Below is a list of health and safety requirements:
- Ensure you take care when handling the knife whilst cutting the lithium sample.
- Wear safety goggles and a lab coat at all times.
- Ensure there is eyewash apparatus available at hand.
- Ensure the room is well ventilated.
