Experiment One: Calibration of and Choosing Glassware
Purpose: The purpose is to show the different techniques involved in using different pieces of
volumetric glassware and how precision and accuracy are affected by the choice of volumetric
glassware. This will be done by generating data and using statistical analysis.
Procedure:
Calibration of Pipettes
1. Weigh a clean, dry weighing bottle 5 times and record results.
2. Use 1mL pipets to fill to the mark and weigh.
3. Repeat process 5 times for 1mL pipet.
4. Repeat Steps 2-4 for 2mL and 5mL pipets.
5. Average data for each pipet.
6. Determine standard deviation and relative standard deviation.
Calibration of Volumetric Glassware:
1. Separately weigh clean and dry 10mL, 25mL, and 50mL volumetric flasks.
2. Fill to the mark of the 10mL volumetric flask and re-weigh.
3. Repeat process five times for 10mL volumetric flask.
4. Repeat Steps 2 and 3 with 25mL and 50mL volumetric flasks.
5. Calculate average weight, standard deviation, and relative standard deviation for all three
flasks.
Data:
Calibration of Pipettes
1
67.7691
2
67.7701
3
67.7694
4
67.77
1 mL
Pipette 1
Trial 1
1.0802
Trial 2
0.9995
Trial 3
0.9915
Trial 4
1.0139
Trial 5
1.0113
Average
1.01928
Total
Average
Standard Deviation
Relative Standard
Deviation
Pipette 2
1.0057
0.984
0.9884
0.9982
1.0104
0.99734
Pipette 3
0.819
1.0094
0.9975
1.0054
0.997
0.96566
Pipette 4
1.0091
1.0047
0.9907
0.9888
0.999
0.99846
Weigh bottle
0.998096
0.0202308
2.02%
5
Average
66.7701 67.56974
Pipette 5
0.9978
1.0046
0.9994
1.0735
0.9734
1.00974
2 mL
Pipette 1
Pipette 2
Pipette 3
Pipette 4
Pipette 5
Trial 1
1.9816
1.9703
1.9859
1.9987
1.9901
Trial 2
1.9978
1.9341
1.9665
1.9933
1.9918
Trial 3
1.9820
1.9934
1.9693
1.9957
1.9934
Trial 4
1.9989
1.9893
1.9458
1.8999
1.9889
Trial 5
1.9900
1.976
1.8722
1.9959
1.9893
Average
1.99006
1.97262
1.94794
1.9767
1.9907
Total
Average
1.975604
Standard Deviation
0.0174088
Relative Standard
Deviation
0.88%
5 mL
Pipette 1
Pipette 2
Pipette 3
Pipette 4
Pipette 5
Trial 1
4.9416
4.9394
4.9395
4.9528
4.9725
Trial 2
4.9348
4.9393
4.9333
4.9601
4.9701
Trial 3
4.9689
4.9320
4.9471
4.9457
4.9598
Trial 4
4.9367
4.9251
4.9458
4.9492
4.9628
Trial 5
4.9302
4.9385
4.9298
4.9511
4.9587
Average
4.94244
4.93486
4.9391
4.95178
4.96478
Total
Average
4.946592
Standard Deviation
0.011924
Relative Standard
Deviation
0.24%
Calibration of Volumetric Glassware
Empty
Volumetric Glass
10 ml
25 mL
50 mL
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Average
13.2727
13.2725
13.273
13.2728
13.2724 13.27268
18.3467
18.3476
18.3476
18.3471
18.3475 18.3473
35.639
35.6392
35.6384
35.6383
35.6382 35.63862
10 mL
Pipette 1
Pipette 2
Pipette 3
Pipette 4 Pipette 5
Trial 1
9.9993
9.9979
9.9993
9.9989
9.9813
Trial 2
10.001
9.9885
10.0035
9.9992
9.9927
Trial 3
9.9895
9.9691
9.9788
9.9833
9.9948
Trial 4
9.9788
9.9413
9.9499
10.0002
9.9981
Trial 5
9.9900
9.9831
9.9639
9.9993
9.9972
Average
9.99172
9.97598
9.97908
9.99618
9.99282
Total
Average
9.987156
Standard Deviation
0.0090065
Relative Standard
Deviation
0.09%
25 mL
Pipette 1
Pipette 2 Pipette 3
Pipette 4 Pipette 5
Trial 1
24.88
24.8346
24.8823
24.8812
24.9196
Trial 2
24.9086
24.8823
24.8917
24.8897
24.9075
Trial 3
24.8912
24.9033
24.9039
24.8791
24.8955
Trial 4
24.9034
24.8911
24.8859
24.8901
24.8897
Trial 5
24.8783
24.8875
24.8958
24.8832
24.8916
Average
24.8923 24.87976 24.89192 24.88466 24.90078
Total
Average
24.88988
Standard Deviation
0.0080388
Relative Standard
Deviation
0.03%
50 mL
Pipette 1
Pipette 2 Pipette 3
Pipette 4 Pipette 5
Trial 1
49.4655
49.8633
49.6750
49.8001
49.5824
Trial 2
49.6820
49.7238
49.6002
49.7984
49.6276
Trial 3
49.6036
49.7495
49.6489
49.7321
49.5785
Trial 4
49.5941
49.8205
49.7068
49.6992
49.7411
Trial 5
49.4992
49.6912
49.7134
49.7612
49.6503
Average
49.56888 49.76966 49.66886
49.7582 49.63598
Total
Average
49.68032
Standard Deviation
0.0845032
Relative Standard
Deviation
0.17%
Calculations:
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑊𝑒𝑖𝑔ℎ𝑡 =
𝑥1 + 𝑥2 + 𝑥3 + 𝑥4 + 𝑥5
5
Ex. 1mL Pipet#1:
1.0802 + 0.9995 + 0.9915 + 1.0139 + 1.0113
= 1.01928
5
(𝑥1 − 𝑎𝑣𝑔)2 + (𝑥2 − 𝑎𝑣𝑔)2 + (𝑥3 − 𝑎𝑣𝑔)2 + (𝑥4 − 𝑎𝑣𝑔)2 + (𝑥5 − 𝑎𝑣𝑔)2
𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝐷𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 = √
𝑛−1
Ex. 1mL Pipet:
(1.01928 − 0.998096)2 + (0.99734 − 0.998096)2 + (0.96566 − 0.998096)2 + (0.99846 − 0.998096)2 + (1.00974 − 0.998096)2
√
4
= 0.0202308
𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝐷𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛𝑛 =
𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝐷𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛
× 100%
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑊𝑒𝑖𝑔ℎ𝑡
Ex. 1mL Pipet:
0.0202308
× 100% = 2.02%
1.01928
Conclusion:
For this lab, different sized pipettes and volumetric glassware were tested for their
accuracy using water. The results of this experiment showed that as the size of glassware or
pipette increased, the standard of deviation decreased. This proved that the larger the glassware
or pipette, the more accurate it is. For example, the calculated standard deviation of the 5mL
pipette was 0.01194, which was smaller than the calculated standard deviation of the 1mL
pipette, which was 0.020238. Overall, the volumetric flasks were more accurate than the
pipettes. Human error, such as extra water left in the flask or an inaccurate measurement of the
pipette, could attest for the abnormal standard deviation calculation for our 50mL volumetric
flask.
After-Lab Questions:
1. Explain using calculations and words whether it is better to use 20, 49, or 56 mL of
solution from a fifty mL buret.
It would be better to use the 49 mL of solution from a fifty mL buret. The 20 mL
would not be better since, as our calculations showed, you want the buret to be filled as
much as possible with as little chance of error. Our calculations showed that the bigger
the buret, the smaller the relative deviation and therefore, less error associated with the
measurements. It also would not be better to use 56 mL of solution since it would be
challenging to have to measure out 50 mL of solution and then add another 6 mL without
some form of human error affecting the results.
2. Assuming the volume of base used had a mean value of 43.56mL with a std dev of 0.89mL using
five titrations, the molarity of base was 0.1012M std dev 0.0025, and the volume of acid had a
mean value of 50mL std dev 0.05mL, what would be the calculated molarity and error associated
with this measurement?
𝑉𝑏𝑎𝑠𝑒 × 𝑀𝑏𝑎𝑠𝑒 = 𝑉𝑎𝑐𝑖𝑑 × 𝑀𝑎𝑐𝑖𝑑
(43.56𝑚𝐿) × (0.1012𝑀) = (0.050𝐿 × 1000𝑚𝐿) × 𝑀𝑎𝑐𝑖𝑑
𝑀𝑎𝑐𝑖𝑑 = 0.088𝑀
% 𝑒𝑟𝑟𝑜𝑟 = √[
0.89 × 100 2
0.0025 × 100 2
0.05 × 100 2
] +[
] +[
]
43.56
0.1012
50
% 𝑒𝑟𝑟𝑜𝑟 = 3.21%