Experiment 1: Calibration of Glassware
Purpose:
The purpose of the experiment is to allow you to understand the correct ways to prepare and use
different types of volumetric glassware in order to obtain the correct measurements. It will also help
you understand the difference between precision and accuracy, and how each is effected by the
different types of glassware.
Procedure:
Calibration of Pipets



Weigh a clean, dry weighing bottle at least 5 times to determine the empty weight and record
the result
Using 1, 2, and 5 mL pipets fill the pipet to the mark and deliver the volume to the weighing
bottle using correct pipeting technique
Repeat delivery and weighing step 5 times for each pipet
Calibration of Volumetric Glassware




Weigh clean and dry volumetric flasks 10, 25, and 50 mL five times
Fill to mark and re-weigh
Perform the fill and weigh step 5 times for each flask
Treat this data as above
Which pipets are more precise and why?
The larger pipets are more precise because there is greater room in error for measurement compared to
a smaller pipet because their measurements are so small; being off by just a little is a greater percent
error than a larger pipet.
Which volumetric flasks are more precise and why?
The larger volumetric flasks are more precise because just like the pipets there is more room to be off in
a measurement and it can still have a smaller percent error, than a smaller flask with the same amount
of measurement error.
Data:
Calibration of Pipets
Clean dry weighing bottle (100mL beaker)
Trial 1
Trial 2
Trial 3
Trial 4
Trial 5
Average
50.1062g
50.1057g
50.1055g
50.1052g
50.1051g
50.10554g
1mL pipet: mass of water
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
Average (g)
Standard
Deviation
Relative
Standard
Deviation
0.9701
0.9809
0.9729
0.9818
0.9778
0.9767
0.0051
.5191%
2mL pipet: mass of water
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
Average (g)
Standard
Deviation
Relative
Standard
Deviation
1.9595
1.9643
1.9608
1.9702
1.9690
1.9647
0.0048
.2430%
5mL pipet: mass of water
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
Average (g)
Standard
Deviation
Relative
Standard
Deviation
4.9582
4.9476
4.9424
4.9577
4.9609
4.9533
0.0079
.1604%
Empty Volumetric Flasks
Volumetric
Flasks (mL)
10
25
50
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
9.3717
19.6647
35.9462
9.3720
19.6647
35.9459
9.3718
19.6648
35.9458
9.3719
19.6646
35.9461
9.3719
19.6646
35.9456
10mL vol flask: mass of water
25mL vol flask: mass of water
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
Average
Standard
Deviation
Relative
Standard
Deviation
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
Average
Standard
Deviation
Relative
Standard
Deviation
0.9701
0.9809
0.9729
0.9818
0.9778
0.9767g
0.0051
.5191%
Calculations:
Average:
Example:
𝑥1 +𝑥2 +𝑥3 +𝑥4 +𝑥5
5
0.9701+0.9809+0.9729+0.9818+0.9778
5
= 0.9767
1.9595
1.9643
1.9608
1.9702
1.9690
1.9647g
0.0048
.2430%
Average Weight
(g)
9.37186
19.66468
35.94592
50mL vol flask: mass of water
Trial 1 (g)
Trial 2 (g)
Trial 3 (g)
Trial 4 (g)
Trial 5 (g)
Average
Standard
Deviation
Relative
Standard
Deviation
4.9582
4.9476
4.9424
4.9577
4.9609
4.9533g
0.0079
.1604%
2
(𝑥 – 𝑎𝑣𝑔)
Standard Deviation: √ 1
2
(0.9701– 0.9767)
Example: √
.0051
×
0.9767
2
2
2
𝑛−1
2
2
2
2
+(0.9809– 0.9767) +(0.9729– 0.9767) +(0.9818– 0.9767) +(0.9778– 0.9767)
Relative Standard Deviation:
Example:
2
+(𝑥2 – 𝑎𝑣𝑔) +(𝑥3 – 𝑎𝑣𝑔) +(𝑥4 – 𝑎𝑣𝑔) +(𝑥𝑛 – 𝑎𝑣𝑔)
4
𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑤𝑒𝑖𝑔ℎ𝑡
= .0051
× 100
100 = 0.5191%
Conclusion:
The point of the experiment was to be precise and accurate in measuring with the pipets and volumetric
flasks. There were many places that error could have taken place when measuring out the volume.
There could have been error if a person didn’t wipe the pipet before depositing the water or if they
didn’t get the last drop out of the pipet. There can also be an error if a person didn’t read the level of
the meniscus right.
From the data collected and the results that were calculated, it shows that the larger the volume of the
pipets or flasks the less percent error there is in measurements. The smaller the pipet or flask the larger
the relative standard deviation is, which means more percent error.
Lab Questions:
1) Explain using calculations and words whether it is better to use 20, 49, or 56mL of solution from a
50mL buret.
It is better to use a 56mL solution from the 50mL buret because 56mL is largest volume. The second
addition of solution to add the extra 6mL might cause a greater percent in error when being
measured.
2) Volume of base had mean value of 43.56mL with std dev of 0.89mL using 5 titrations, molarity of
base was 0.1012M std dev 0.0025, volume of acid had mean value of 50mL std dev 0.05m, what
would be the calculated molarity and error associated with this measurement.
𝑀1 𝑉1 = 𝑀2 𝑉2
0.1012𝑀 × 43.56𝑚𝐿 = 𝑀2 × 50𝑚𝐿
𝑀2 = 0.0882𝑀
2
2
2
0.89
.0025
.05
% error= √(43.56) + (.1012) + ( 50 ) × 100% = 3.21%