Expt 1 Cal of Pipette

Experiment #1: Calibrating a 10-mL volumetric pipet (a bring home experiment)
prepared by r. a. mindo
Student Learning Objectives:
 Demonstrate the proper handling of the pipet and the pipet bulb in dispensing a 10-mL volume.
 Create a control chart of the data.
 Analyze the data and examine how well (in terms of precision and accuracy) was the experiment done.
Introduction
In this experiment; we will apply the lessons we learned in Chapter 6: Random errors in Chemical Analysis,
specifically; calculating standard deviation, and confidence intervals or critical limits. Through these statistical
parameters; we will be able to examine how well you are able to deliver the 10.00 mL portions using a 10-mL volumetric
pipet.
Glassware and materials needed:
1 – 10 mL volumetric pipet 10 – test tubes (pre-weighed) 500 mL distilled water
1 – pipet bulb 10 – rubber stoppers 1 - Digital thermometer
1 – test tube rack 1 – 500 mL beaker 1 – wash bottle
Proper techniques in using a volumetric pipet.
Watch the following instructional videos before attempting to use the pipet.
Types of pipet: serological pipet and standard pipet https://youtu.be/fG6FwBTCvok or https://youtu.be/hO-

yTT_qCe4
Understanding serological pipets https://youtu.be/WGLivRvsh5w
Using and reading a graduated pipet https://youtu.be/rL1KxXvwzL4
How to use the pipet and the pipet bulb https://youtu.be/Wrr5zH9ea1s
Preparing the pipet
Obtain a 10-mL pipet and wash it with liquid detergent and rinse it with tap water. Once the soap suds are removed, rinse it
with distilled water. Allow it to air dry for a few minutes. Study the pipet. What type of pipet are you using? What is the
volume of the smallest division of the pipet’s scale? Make a drawing of the pipet, show the volume markings.
Practice pipetting
Practice using the pipet bulb and pipet; try to dispense 10 mL distilled water to a beaker a few times. Keep on practicing
until you are comfortable with handling the pipet.
Before you proceed to the experiment, I would like to check your pipetting technique. Create a video in flipgrid showing
how you handle your pipet. I will give the go signal for you to proceed to the experiment once I see that you are proficient with the
use of the pipet.
I. Calibration of 10-mL pipet

1. Obtain at least 10 clean and dry test tubes with corks or rubber stoppers. Label the test tubes properly. Measure the initial
weights of the test tube and its cover using the Analytical balance. Use a clean and dry 125 mL Erlenmeyer flask to help the
test tube stand on the balance pan. Hold the test tube with a tissue paper or paper towel, not with your hands, to avoid
changing its mass with fingerprint residue. (Your instructor performed this part of the experiment, the initials weights and
the final weights of the test tubes will be given after you return the test tubes and the borrowed materials. Do not exchange
the labels of the test tubes nor exchange the stoppers of the test tubes.)
2. Using the calibrated thermometer, read the temperature of the distilled water used for this experiment.
3. Dispense 10 mL distilled water to the pre-weighed test tubes and cover the test tubes. Hold the test tube with a tissue
paper or paper towel, not with your hands.
4. Measure the weights of the test tubes with its contents using the analytical balance. (Your instructor will perform this part
of the experiment. Carefully package the glassware and ask your parents or guardians to return the materials to the School.
The items are to be delivered to the Community Center entrance by Tuesday, July 27 noon time.)
II. Calculation of results

1. Calculate the mass of water delivered by subtracting the weight of test tube + cover + 10-mL water with the initial weight of
the test tube + cover.
2. Use Table 1 to convert the mass of water to the volume delivered.
3. Calculate the difference of volume between the volume delivered and the volume of the pipet.
'
V pipet =true volume dispensed by pipet−10.00 … e q n . 4
4. Calculate the average volume of dispensed water. Subtract this volume from the volume of the pipet. Round off the volume
difference to two decimal places. This is the correction volume for the pipet.
correction volume of the pipet=average true volume of water −10.00 mL … e q ' n . 5

(Round off to 2 decimal places)
5. Label the pipet with the correction volume, date of calibration and your name.
Appendix:
Table 1 [4]
True volume = (grams of water) x (volume of 1 gram of H 2O corrected to 20 °C) …eq’n. 7
Volume of 1 gram of water (mL)

Temperature (°C) Density (g/mL) At temperature shown a Corrected to 20°C b
10 0.9997026 1.0014 1.0015
11 0.9996084 1.0015 1.0016
12 0.9995004 1.0016 1.0017
13 0.9993801 1.0017 1.0018
14 0.9992474 1.0018 1.0019
15 0.9991026 1.0020 1.0020
16 0.9989460 1.0021 1.0021
17 0.9987779 1.0023 1.0023
18 0.9985986 1.0025 1.0025
19 0.9984082 1.0027 1.0027
20 0.9982071 1.0029 1.0029
21 0.9979955 1.0031 1.0031
22 0.9977735 1.0033 1.0033

23 0.9975415 1.0035 1.0035
24 0.9972995 1.0038 1.0038
25 0.9970479 1.0040 1.0040
26 0.9967867 1.0043 1.0042
27 0.9965162 1.0046 1.0045
28 0.9962365 1.0048 1.0047
29 0.9959478 1.0051 1.0050
30 0.9956502 1.0054 1.0053
31 0.9953440 1.0055
32 0.9950292 1.0058
33 0.9947060 1.0061
34 0.9943745 1.0063
35 0.9940349 1.0066
a - corrected for buoyancy with the equation:
m=
'
m 1−
( da
dw )
( 1− dd )a
da is the density of air (0.0012 g/mL) near 1 atm and 25 °C

dw is the density of the calibration weights (typically 8.0 g/mL)
d is the density of the object being weighed
b - corrected for buoyancy and expansion of borosilicate glass (0.0010 % K -1)

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Experiment #1: Calibrating a 10-mL volumetric pipet (a bring home experiment)

Student Learning Objectives:

Glassware and materials needed:

1 – 10 mL volumetric pipet 10 – test tubes (pre-weighed) 500 mL distilled water

1 – pipet bulb 10 – rubber stoppers 1 - Digital thermometer

1 – test tube rack 1 – 500 mL beaker 1 – wash bottle

Proper techniques in using a volumetric pipet.

Types of pipet: serological pipet and standard pipet https://youtu.be/fG6FwBTCvok or https://youtu.be/hO-

Understanding serological pipets https://youtu.be/WGLivRvsh5w

Using and reading a graduated pipet https://youtu.be/rL1KxXvwzL4

How to use the pipet and the pipet bulb https://youtu.be/Wrr5zH9ea1s

Preparing the pipet

I. Calibration of 10-mL pipet

II. Calculation of results

correction volume of the pipet=average true volume of water −10.00 mL … e q ' n . 5

True volume = (grams of water) x (volume of 1 gram of H 2O corrected to 20 °C) …eq’n. 7

Volume of 1 gram of water (mL)

22 0.9977735 1.0033 1.0033

da is the density of air (0.0012 g/mL) near 1 atm and 25 °C

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