Experiment 1
Calibration of and Choosing Glassware
Purpose: To introduce different types of glassware, and the techniques involved in using them. Then
by using statistical analysis one will see how precision and accuracy are affected by
glassware.
Procedure:
Calibration of pipets:
o Weigh a clean dry beaker
o Place a sample of water in the beaker using a 1mL pipet
o Repeat steps until 5 data points are collected
o Repeat with a 2 and 5mL pipet
Calibration of Volumetric Glassware:
o Weigh a clean and dry volumetric flask 10mL
o Fill to mark with water and re-mass
o Repeat steps until 5 data points are collected
o Repeat with a 25, 50mL volumetric flask
Data:
Calibration of Pipet
Trial
Mass of Empty
Mass of 1mL
Mass of 2mL
Mass of 5mL
Beaker (g)
Pipetted Water
Pipetted Water
Pipetted Water
and Beaker (g)
and Beaker (g)
and Beaker (g)
1
80.0442
81.0335
81.9957
85.0128
2
80.0417
81.0209
81.9596
85.0127
3
80.0415
81.0209
81.9949
85.0027
4
80.0418
81.0307
81.9846
84.9877
5
80.0400
81.0296
81.9964
84.9952
Avg.
80.0418
81.0299
81.9862
85.0022
Trial
Mass of 1mL Pipetted
Mass of 2mL Pipetted
Mass of 5mL Pipetted
Water (g)
Water (g)
Water (g)
1
0.9917
1.9539
5.0000
2
0.9791
1.9178
4.9999
3
0.9791
1.9531
4.9899
4
0.9889
1.9428
4.9749
5
0.9878
1.9546
4.9824
Avg.
0.9853
1.94444
4.9894
Calibration of Volumetric Flask
V.F.= Volumetric Flask
Trial
Mass of
Mass of
Mass of
Mass of
Mass of
Mass of
Empty 10mL
10mL V.F.
Empty
25mL V.F.
Empty
50mL V.F.
V.F. (g)
and Water
25mL V.F.
and Water
50mL V.F.
and Water
(g)
(g)
(g)
(g)
(g)
1
9.3546
19.3053
20.1689
45.0807
35.8745
86.6069
2
9.3544
19.3048
20.1684
45.0806
35.8744
86.6052
3
9.3542
19.3037
20.1681
45.0804
35.8770
86.6044
4
9.3546
19.3041
20.1683
45.0799
35.8727
86.6039
5
9.3546
19.3041
20.1685
45.0800
35.8737
86.6041
Avg.
9.3546
19.30432
20.1685
45.0803
35.8739
86.6049
Experiment 1
Calibration of and Choosing Glassware
Trial
Mass of Water 10mL
V.F. (g)
Mass of Water 25mL
V.F. (g)
Mass of Water 50mL
V.F. (g)
1
2
3
4
5
Avg.
9.95084
9.95034
9.94924
9.94964
9.94964
9.94994
24.91224
24.91214
24.91214
24.91194
24.91154
24.91186
50.73304
50.73134
50.73054
50.73004
50.73024
50.73104
Statistical Analysis
Standard Deviation
1mL Pipet
0.005853375
Relative Standard Deviation
0.594058285
2mL Pipet
0.015653211
0.805024096
5mL Pipet
10mL V.F.
0.010978479
0.000640312
0.220036055
0.00643534
25mL V.F.
0.000279285
0.001121092
50mL V.F.
0.001222702
0.002410165
Calculations:
mwater=mwater&glasswarememptygalssware
Σ𝑥
𝑥̅ =
𝑛
n= Number of Trials
x=Measurement from Trial
̅=Average of Trials
𝒙
𝑠=√
Σ(𝑥 − 𝑥̅ )
𝑛−1
s= Standard Deviation
mwater=81.0335g-80.0442g=0.9917g
𝑥̅ =
80.0442 + 80.0417 + 80.0415 + 80.0418 + 80.0400
5
𝑥̅ = 80.0418
(0.9917 − 0.9853)2 + (0.9791 − 0.9853)2 + (0.9791 + 0.0853)2 + (0.9878 + 0.9853)2 + (0.9878 + 0.9853)2
𝑠=√
5−1
s=0.005853375
100 × (𝑠)
𝑥̅
RSD=Relative Standard
Deviation
𝑅𝑆𝐷 =
𝑅𝑆𝐷 =
100 × (0.005853375)
0.9853
RSD=0.594058285
Conclusion:
The piece of volumetric glassware that had the lowest standard deviation and therefore was
the most precise was the volumetric flask. One of the reasons for the larger error with the pipets,
pipetting takes a more difficult technique to measure out the desired amount. For less experienced
chemists who haven’t refined their technique this is a significant error. Another error that occur is
due to a miss understanding of procedure, instead of weighing the empty glassware after each trial it
was weighed five times in the beginning to which an average mass was taken. This error is due to left
over water in the glassware that was not taken into account.
Experiment 1
Calibration of and Choosing Glassware
Post Lab Questions:
1.
With every piece volumetric glassware there is always going to be some error associated
with it, chemists reduce this by using the right kind of glassware when doing an experiment. An
example of this is with a buret, which is another commonly used piece of glassware. If 20mL of
solution is needed measured out, one would want to use the appropriated buret, a 50mL buret would
introduce unneeded error into the experiment so it would be best to use a 25mL buret. The next
experiment calls for 56mL of solution, you again would not want to use a 50mL buret because you
would uses the entire buret plus have to refill and add 6mL more. This again adds unneeded error to
your experiment. Now lets say that 49mL of solution are needed, a 50mL buret would be a perfect fit
for the job, it holds enough solution to satisfy the needs of the experiment, this reduces the chances
for error.
2.
𝑀𝑏𝑎𝑠𝑒 × 𝑉𝑏𝑎𝑠𝑒 = 𝑀𝑎𝑐𝑖𝑑 × 𝑉𝑎𝑐𝑖𝑑
(43.56𝑚𝐿)(0.1012𝑀)
= 𝑀𝑎𝑐𝑖𝑑
50𝑚𝐿
Macid=0.0882M
𝑒1 =
0.89
0.0025
0.05
× 100% = 2.04% 𝑒2 =
× 100% = 2.47% 𝑒3 =
× 100% = 0.1%
43.56
0.1012
50
%𝐸𝑟𝑟𝑜𝑟 = √(2.04%)2 + (2.47%)2 + (. 1%)2 = 3.21%
Macid=0.0882M ±3.21%
Macid=0.0882M±0.0028