Experiment 1: Calibration of Glassware
Introduction:
This experiment is meant to supply information involving the error related to laboratory glassware. To determine
the accuracy and precision of graduated pipettes and volumetric flasks they will be calibrated. This data will be a guide to
use when choosing glassware to use for future experiments.
Procedure:
Calibration of Pipettes:
A clean/dry beaker was weighed empty five times. Using a 1mL pipette water was added to the beaker and it was
reweighed. This was repeated 4 times. The same procedure was done using both 2mL and 5mL pipettes. The
recorded weights were then averaged.
Calibration of Volumetric Flasks:
Clean/dry volumetric flasks were weighed empty five times. They were then filled to the line and reweighed. This
was done five times with three different flasks, 10mL, 25mL and a 50mL. The weights were recorded and then averaged.
Raw Data:
Calibration of Pipettes:
Trial
Empty beaker mass
1mL H2O and
(g)
beaker mass (g)
1
63.7374
64.7276
2
63.7377
64.7233
3
63.7370
64.7251
4
63.7368
64.7176
5
63.7367
64.7255
Average
63.7371
Calibration of Volumetric Flasks:
Trial
Empty 10mL
Filled
Empty
flask mass (g)
10mL flask
25mL flask mass
mass (g)
(g)
1
13.1499
23.0284
20.0235
2
13.1498
23.0494
20.0234
3
13.1494
23.0398
20.0233
4
13.1494
23.0380
20.0233
5
13.1495
23.0224
20.0233
Avg
13.1496
20.0234
Calculated Data:
Mass of the water:
Trial
Mass 1mL
Mass 2mL
Mass 3mL
H2O (g)
H2O (g)
H2O (g)
1
0.9905
1.9815
4.9542
2
0.9862
2.0124
4.9627
3
0.9880
2.0431
4.9755
4
0.9805
2.0141
4.9705
5
0.9884
1.9892
4.9684
Average
0.9867
2.0081
4.9663
1mL Pipette
2mL Pipette
5mL Pipette
10mL Volumetric Flask
25mL Volumetric Flask
50mL Volumetric Flask
Standard Deviation
0.00378289
0.024208738
0.008229642
0.010487135
0.013654413
0.0305858148
2mL H2O and
beaker mass (g)
65.7186
65.7495
65.7802
65.7512
65.7263
Filled
25mL flask
mass (g)
44.9430
44.9429
44.9707
44.9650
44.9671
Mass 10mL
H2O(g)
9.8788
9.8998
9.8902
9.8884
9.8728
9.8860
5mL H2O and
beaker mass (g)
68.6913
68.6998
68.7126
68.7076
68.7055
Empty 50mL
flask mass (g)
Filled 50mL
flask mass (g)
48.8231
48.8229
48.8228
48.8227
48.8227
48.8228
98.4459
98.4127
98.4366
98.3991
98.3693
Mass 25mL
H2O(g)
24.9196
24.9195
24.9473
24.9416
24.9437
24.9344
Mass 50mL
H2O(g)
49.6231
49.5899
49.6138
49.5763
49.5465
49.5899
Relative Standard Deviation
0.384948727
1.205590431
0.165713051
0.106080669
0.054761391
0.061677531
Calculations:
Average mass equation:
̅=
𝒙
Average mass example:
Σx
n
(63.7374g + 63.7377g + 63.7370g + 63.7368g + 63.7367g)
5
̅ = 𝑎𝑣𝑔. 𝒐𝒇 𝒎𝒆𝒂𝒔𝒖𝒓𝒆𝒎𝒆𝒏𝒕𝒔
𝒙
𝑥̅ =
𝒙 = 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝒎𝒆𝒏𝒕
𝑥̅ = 63.7371𝑔
𝑛 = # 𝑜𝑓 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡𝑠
Mass of water equation:
Mass of water example:
𝒎𝒘𝒂𝒕𝒆𝒓
̅ 𝒆𝒎𝒑𝒕𝒚
= 𝒎𝒇𝒊𝒍𝒍𝒆𝒅 𝒈𝒍𝒂𝒔𝒔𝒘𝒂𝒓𝒆 − 𝒎
𝑚𝑤𝑎𝑡𝑒𝑟 = 64.7276𝑔 − 63.7371𝑔
𝑚𝑤𝑎𝑡𝑒𝑟 = 0.9905𝑔
Standard deviation equation:
𝒔=√
̅)𝟐
𝚺(𝒙 − 𝒙
𝒏−𝟏
Standard deviation example:
(63.7374−63.7371)2 +(63.7377−63.7371)2 +(63.7370−63.7371)2 +(63.7368−63.7371)2 +(63.7367−63.7371)2
𝑠=√
5−1
𝑠 = 0.003798289
𝒔 = 𝒔𝒕𝒂𝒏𝒅𝒂𝒓𝒅 𝒅𝒆𝒗𝒊𝒂𝒕𝒊𝒐𝒏
Relative standard deviation
equation:
𝑹𝑺𝑫 =
𝟏𝟎𝟎 ∗ (𝒔)
̅
𝒙
𝑹𝑺𝑫 = 𝒓𝒆𝒍𝒂𝒕𝒊𝒗𝒆 𝒔𝒕𝒅. 𝒅𝒆𝒗𝒊𝒂𝒕𝒊𝒐𝒏
Relative standard deviation example:
𝑅𝑆𝐷 =
100 ∗ (0.003798289)
63.7371
𝑅𝑆𝐷 = 0.384948727
Discussion:
Burets are another commonly used type of glassware and as always there are different errors associated with them.
This is important to take into account when choosing which volume to use for a specific amount of liquid. It is important to
use the correct buret for the appropriate amount of solution. If you needed to dispense 20mL of solution you would not use
a 50mL buret because it would allow for unneeded error when you could instead use a 25mL buret. If you wanted to
dispense 56mL of liquid once again a 50mL buret would not be the right choice because you would have to refill it and then
only use 6mL and that would cause unnecessary error when you could just use a different buret. In the case of dispensing
49mL of solution of 50mL buret would work nicely and cause the smallest amount of error.
For every measurement there is an associated error, which can contribute the error in every calculation with the
measurement. Whenever a calculation is made with measurements the error must also be calculated using the error
associated with each measurement used in the original calculation. A commonly used calculation is the dilution equation
(M1V1= M2 V2). This can be used to find the molarity of a solution that is being prepared. Since the volume and the
molarity of the stock solution are both know there are known errors that go along with those values. The dilution equation
to find the molarity involves both multiplication and division so in order to find the associated error of the calculated
molarity it would have to be a percentage. To do so you would take the square root of the sums of the squares of all the
percent errors of the measurements involved in the calculation. (i.e. stock M, stock V, and prepared V) By using every
measurements associated error it represents that every single measurement adds to the overall error this is known as the
propagation of error.
Conclusion:
The calculations of the relative standard deviations from the experiment could only conclude that overall that the
volumetric glassware is more precise than the pipettes. This conclusion is not exact due to errors that occurred during the
experiment. The precision difference between the volumetric flasks and the pipettes could be due to errors outside of the
glassware. Pipetting requires more technique than filling a volumetric flask and there could be error involved with the
actual pipetting technique. Another error was completely the procedure correctly and misreading the procedure. Instead of
reweighing the empty glassware after each trial it was weighed empty five times at once. Also there is no way that the
glassware was fully dried in between each trial. The calculated relative standard deviation values fell in the accepted range,
but the if the experiment was done a second time the results could come out more precisely if the procedure is followed
more closely and more attention to detail is paid.