CHEM 321 Northern Virginia Community Calibration of Laboratory Glassware Essay

QUANTITATIVE CHEMICAL ANALYSIS LABORATORY: CHEM 321 LABCHEM 321 LAB
Calibration of Laboratory Glassware
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(Read Harris, Chapter 2: Tools of the Trade before doing this lab)
Background
There are three types of containers used in a laboratory, volumetric, ordinary and disposable glassware,
used either to contain (TC) or to deliver (TD) liquids.
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Volumetric glassware is a container that has been calibrated at a specific temperature to deliver
or contain ACCURATE amounts of liquid, examples of volumetric glassware that we will use
includes burets, volumetric pipets and volumetric flasks.
Ordinary glassware has less precise volume calibrations and is used whenever the volumes do
not have to be measured as accurately, examples include beakers, Erlenmeyer flasks and
graduated cylinders.
Disposable glassware (or plastic ware) is used to transfer or hold liquids temporarily and may
not contain any volume markings; examples include medicine droppers and disposable pipets.
Purpose and Principle
The purpose of this experiment is to calibrate analytical volumetric glassware commonly used in
laboratories for chemical analysis. The principle is based on weighing a known volume of water at a
constant temperature. Therefore, the apparent volume can be calculated from the relation: apparent
volume = weight / density. Here, weight and density must be known precisely and accurately. The error
in apparent volume is calculated knowing the error in weight and density through error propagation.
The final result must be expressed with an error with 95% confidence interval.
This experiment will expose you to a variety of important concepts related to quantitative
experimentation, including the proper use of volumetric glassware, analytical balance, error
propagation, and statistics. You will calibrate a 25.0 mL volumetric flask, a 25.0 mL measuring cylinder,
a 10.0 mL pipet, and a 50.0 mL buret. You will experimentally determine what volume they actually
contain and the measurement errors with a desired confidence.
Calibration of glassware is carried out by weighing the amount of water contained or delivered with an
analytical balance within ± 0.0002 g absolute uncertainty. Since the density, or weight per unit volume
of water changes about 0.03% per oC at 25 oC, the temperature of the water must be known accurately.
The actual volume delivered can be obtained from a table relating temperature to volume, which can be
located in your textbook. Although errors in buret and pipet markings by the manufacturer are usually
small, they cannot be neglected. Ask yourself if this error systematic or random.
Procedure
1) Make sure you understand the proper use of the analytical balances and volumetric glassware. A
basic review can be found in your text (Harris, Chapter 2: Tools of the Trade)
2) Before you begin, make sure your glassware is CLEAN. Water should run out smoothly, leaving a thin
film on the inside of the glass. It should not “bead” on the inside. Be sure to note the type of the
glassware before calibration.
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3) Place about 800 mL of deionized water in a 1000 mL beaker with a thermometer. Allow the
temperature of the water to equilibrate to room temperature. Record the water temperature. Why is
this important?
4) Note the specification given for the maximum weight allowance of the balance. Why is this
important?
5) Calibration of a 50.0 mL buret
a) Fill buret with DI water and remove air bubbles from the water column and tip by draining the buret.
If you see any water beads form in the buret, clean the buret and start over.
b) Refill the buret so the meniscus is just under 0.00 mL. Drain water to have a continuous water column
without bubbles trapped at the tip of the buret. Refill and readjust as necessary.
c) Using gloves preweigh a 25.0 mL volumetric flask on the analytical balance, giving the water in the
buret time to settle. Here, the flask is just a container to weigh the water. Large containers are too
heavy to weigh in an analytical balance. If the water drips or leaks tighten the stopcock and allow the
water to settle. Do step b again. (Why must gloves be worn?)
d) Drain ~5.0 mL (read the buret to two decimal) of water into the pre-weighed flask slowly (in step c).
Allow 30 seconds for the film of liquid on the outer walls to descend, record the new liquid level. Find
the amount of liquid delivered by difference.
e) Weigh the flask again to determine the mass of water delivered.
f) Drain the another 5.0 mL from the buret and repeat procedures d and e. Thus you should get 10 data
points form the full 50.0 mL buret volume. Record your data in a tabular form.
g) Calculations: All entries must be present in your lab notebook. The worksheet given is just an example
of the table. Do not submit this worksheet unless instructed. Plot this data: Correction, mL vs. volume
delivered, mL. You should use this buret for the entire semester and keep this graph handy for error
calculation.
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6) Calibration of a 25.0 mL volumetric flask
a) Weigh the clean and dried volumetric flask to the nearest tenth of a milligram on an analytical
balance.
b) Fill the flask with distilled water (made in step 3) just below the 25.0 mL mark.
c) Carefully add water with a disposable pipet until the bottom of the meniscus coincides with the
calibration line. Remove droplets of water present above the line with a lint-less Kimwipe.
d) Reweigh the flask and record the mass.
e) Immediately after weighing, measure and record the temperature of the water in the flask if not using
water from step 3.
f) Calculate the true volume contained in the volumetric flask by using the difference in mass and
temperature correction. Obtain at least three measurements by emptying the flask. Find the average
and the error in your measurement.
7) Calibration of a 25 mL graduated cylinder
a) Place a clean, dry graduated cylinder on the analytical balance and record mass and remove from lab
scales.
b) Pour some of the water from step 3 into the graduated cylinder. Remember to remove any water
bubbles from the liquid first and then remove any droplets from the inside or outside of the cylinder. Fill
the cylinder to ~25 mL, read the volume as precisely as possible and record.
c) Place the cylinder on the scales and record the mass of the water.
d) Repeat for trials 2 & 3 (up the five trials if you choose). Remember that you need not clean and dry
the cylinder between each trial.
10) Calculate the true volume contained in the measuring cylinder by using the difference in mass and
temperature correction. Find the average and the error in your measurement.
8) Calibration of a 10.0 mL volumetric pipet
a) Ask your instructor to show how to use a volumetric pipet. You should practice the fill and delivery
from your pipet several times to get precise volume delivery. Your pipet must deliver without water
droplets sticking to the wall.
b) Fill and deliver the pipet content (water from step 3) into an empty preweighed 25.0 mL volumetric
flask.
c) Place the flask on the analytical balance and record the mass of the water.
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d) Repeat steps b and c at least twice (or more) to get precise results i.e., lower standard deviation. You
need not to clean the weighing flask if you know the initial weight.
e) Calculate the true volume contained in the pipet by using the difference in mass and temperature
correction. Find the average and the error in your measurement.
Data and Results
Calculations for Volumetric Equipment Calibration:
1) Enter the calculated masses and volumes in your laboratory notebook.
2) Calculate:
the mean (average) volume
the standard deviation
the relative standard deviation (%RSD)
the 95% confidence interval
the % relative error (What is your theoretical volume?)
(all errors must be expressed with one significant figure with second figure in subscript: ± 0.2 3 )
3) Construct a reference table of this data and write it in your lab notebook.
Example calculation for a 10.0 mL volumetric pipet
Temperature of Water:
26 OC
Weight of Flask and Water:
Weight of Flask:
Apparent Weight of Water Delivered:
24.6880 g
-14.7130 g
9.9750 g
True Volume of Pipet:
10.02 mL
At 26 OC, 1.0000 g of water occupies 1.0043 mL (Quantitative Chemical Analysis Table 2.7). The true
volume of 9.975 g of water at 26 OC is 9.975 g x 1.0043 mL/g = 10.02 mL
(Note: Confirm the proper number of significant figures.)
Things to consider throughout the experiment and to include in your notes in your laboratory
notebook and your report
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Comment on whether or not the correction volume is within the error allowed for your
volumetric glassware.
Why is it important to do a temperature conversion for the water that you used while
calibrating your glassware? What were the corrections that you took into account? Did you
record your temperature more than once? Did the temperature in the laboratory change during
the duration of the experiment?
Most volumetric glassware is calibrated at what temperature?
What sort of errors do you expect from the analytical balance measurements? What precision
can you expect from the analytical balance? What if you forgot to tare the balance?
What is the best way to read a buret?
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What do the letters T.C. and T.D. found on various types of volumetric glassware signify?
Example tables
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Taken from Harris
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(This is an example of short format lab report. Do not copy the content)
CALIBRATION OF LABORATORY GLASSWARE
Your Name *, Your Partner’s Name
CHEM 321: Quantitative Chemical Analysis Laboratory, GMU
(Experiment date: Feb. 14; Date of submission Feb. 21, 2021)
ABSTRACT
Chemists use precision glassware to prepare and measure solutions for routine
experimentation. The purpose of this lab is to find the accuracy and precision of such
glassware. For this experiment, four different types of glassware: a measuring cylinder,
a buret, a volumetric flask, and a pipet were calibrated for the actual volume they
contain or deliver. The volume correction of water delivered by a buret was found to
range from -0.3 mL to +0.4 mL (one trial). The exact volume contained in the measuring
cylinder, the volumetric pipet, and the measuring cylinder were calculated from the
measurement of …..The errors reported here are within 95% CL and based on the t-test.
The 25.0 mL volumetric flask was found to contain 25.5406 (±0.007 3) mL, the 10.0 mL
pipet contained 10.2301 (±0.0037) mL, and the 25.0 mL measuring cylinder contained
25.1234 (±0.0063) mL of DI water. All replicate measurements were obtained with less
than 0.14 % rsd. These data clearly show that measured volume is precise to three
decimal places. All calculations took into consideration the literature value of density of
laboratory at 17.0 ± 0.1˚C.1
Notes: Watch out for proper significant figures in numbers and errors throughout in this lab.
References and notes should be placed as footnotes.
1
Experimental Data, Results, and Discussion:
Write few sentences to introduce the section…
Show your table and graph and discuss the results.
Write any relevant observations, measurement errors, and their sources.
Buret calibration
Table 1: Calibration of buret (50 mL)
Show your table
Discuss your table
Table 1 contains the experimental data and calculations for the calibration of a 50 mL
buret, with a factory tolerance of ±0.1 mL, with DI water. ….
Show your calibration graph for the buret
Calibration of 50.0 mL buret (# 6)
0.5
0.4
Correction, mL
0.3
0.2
0.1
0
-0.1
0
10
20
30
40
50
60
-0.2
-0.3
-0.4
Volume delivered, mL
Figure 1. Clearly describe the figure. The figure caption should be meaniningful.
(Keep a copy of this graph in your folder for future use. Use the same buret throughout
the semester).
Pipet calibration
Show table, discuss results and the source of error.
Volumetric flask calibration
Show table, discuss results and the source of error.
Measuring cylinder calibration
Show table, discuss results and the source of error.
Conclusion:
The experiments clearly show that all glassware in the laboratory has different degrees
of error associated with them, whether it is measuring the volumes contained (TC) or
delivering volumes (TD). By calibrating laboratory glassware, it is possible to calculate
the random error associated with an experiment. All systematic errors were removed by
calibrating the glassware.
The results clearly show that measured volume is precise to three decimal places.
Therefore, the use of a less precise balance is possible. All calculations took into
consideration the literature value of density/temperature conversion of water due to
the laboratory water being 17.0 ± 0.1˚C. The slight temperature variation over the entire
lab period (only if you measured over the entire period) was not considered for error
propagation. (You can put some the critical conclusions in the abstract)
Example Calculations: (these may be typed or hand written)
One example calculation for each type must be shown in your lab report. For this lab,
you must have example calculation for water mass converted to water volume, average,
standard deviation, %rsd, and error at t95%, n-1. . Also, show error propagation if any.
Questions:
Answer all questions. Write the question first.
Reference:
References should be placed in footnotes2 or endnotes. Use proper journal format (any
American Chemical Society journal). Always try to cite the primary reference. Secondary
and tertiary references are not reliable. Do not cite from web unless they are authentic.
Supplementary materials:
Attach your lab notebook carbon copies or printout from instruments.
2 Check for examples in your quant text.
Calibration of Laboratory Glassware
CHEM 321: Quantitative Chemical Analysis Laboratory
09.02.2022
Introduction
The purpose of this experiment is to determine the mass of liquid the
glassware will hold, and to divide this mass of liquid by the density of
the liquid, obtaining the corresponding volume of liquid. Density is
affected by temperature, so it is necessary to measure the liquid
temperature and look up appropriate density values. This experiment
will represent a diversity of important concepts related to quantitative
experimentation, analytical balance, error, and statistics. In this
experiment, by using clean 50.0 ml buret, DI water, thermometer,
graduated cylinder, we will be able to examine the procedure and note
the result.
Material
• 50.0 ml buret
• Volumetric Flask
• Graduated Cylinder
• DI water
• Thermometer
Procedure
Before starting the experiment, we need to be sure that a buret is
clean, and water can smoothly run out throughout the buret.
Volumetric flask will be filled with DI water, and thermometer will
be placed in the flask in order to record the temperature of water
that will be tested for buret calibration. Once the buret is filled
with 50.0 ml of DI water, the experiment will begin. Water
temperature is 22 Centigrade. 4ml of water in a buret will be
transferred to the graduated cylinder, and will be weighted and
recorded in the table. Next step is to transfer another 4 ml of DI
water inside the buret to the graduated cylinder, then graduated
cylinder will be weighted and recorded. Third step is to add 2ml of
water from buret and weighted then recorded. Since, the
graduated cylinder is 10.0ml, the water needs to be removed and
the procedure will be start all over again until the 50.0ml of DI
water in the buret is finished for the experiment.
Observation
The purpose of the experiment of calibration of volumetric
glassware is to calibrate certain measurement by using volumetric
glassware. The calibration was done by measuring the mass of
water contained in the buret by using graduated cylinder. The
density of water at a 22C temperature was measured for each
data to convert mass into volume.
Conclusion
In conclusion, this experiment is conducted to investigate how to
calibrate the liquid accurately by using volumetric glassware.
Questions
Why is it important to do a temperature conversion for the water
that you used while calibrating your glassware? What were the
corrections that you took into account? Did you record your
temperature more than once? Did the temperature in the
laboratory change during the duration of the experiment?
Density is affected by temperature, so it is necessary to measure
the liquid temperature and look up appropriate density values.
Most volumetric glassware is calibrated at what temperature?
20 degrees C
What sort of errors do you expect from the analytical balance
measurements? What precision can you expect from the
analytical balance? What if you forgot to tare the balance?
What is the best way to read a buret?
It must be at eye level with the bottom of the meniscus to read
the burette.