Experiment 2 - Calibration of Volumetric Glassware

ADORNA JR., JOEMER A. PITAGAN, PAULA JESSIKA C.

CALIBRATION OF VOLUMETRIC GLASSWARE EXPERIMENT # 2

JUNE 2, 2013

MALAYAN COLLEGES LAGUNA

EXPERIMENT # 2

CALIBRATION OF VOLUMETRIC GLASSWARES

Experiment 2: Calibration of Volumetric Glassware 1 | P a g e

I. OBJECTIVES

To identify different types of volumetric glassware;

To discuss the importance of calibrating volumetric instruments;

To calibrate volumetric glassware; and

To use volumetric glassware properly.

II. LABORATORY EQUIPMENT / INSTRUMENTS / REAGENTS

Equipment/Accessories Quantity

25 mL volumetric pipet 1 10 mL volumetric pipet 1 50 mL buret 2 Aspirator 1 Analytical balance 1 Iron stand 1 50 mL beaker 2 250 mL beaker 2 125 mL Erlenmeyer flasks 2 Thermometer 1 Parafilm 1 Buret holder 1 Distilled water in wash bottle 1

III. DISCUSSION OF FUNDAMENTALS

Introduction

In the life of a simple average person, he measures everyday things with a little something

called "estimate", especially to liquids, things, and the like. But to scientists, estimation is out of the

question. Scientists, especially chemists, do not take second chances when measuring volatile

reactive liquids into their reactions. A minute addition or subtraction to it might cause explosions,

unexpected or non-visual reactions. This is very critical especially in the pharmaceutical or in the


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food industry. If you accidentally killed a person with a confident estimate, then chances are you are

on the verge of your pulling conscience, if you have one.

Like the first experiment, measuring volumes are as fundamental as measuring mass. But they

are a little more crucial when it comes to measuring liquid volume. Unlike solids, they more

significantly respond to changes in pressure and temperature, which is particularly dynamic, even in

a laboratory setting. In doing so, volumetric devices for measurements are used.

The type of volumetric device to be used for a particular measurement considers four factors:

general goal of the volume measurement, volume or range of volumes to be measured, degree of

reliability needed for the measurement and number of measurements to be made. Calibration of

these devices is important, as the reasons are stated above.

Theory

Volume like mass is another fundamental property of matter that is commonly determined in

analytical measurements. For solids, volume can be obtained through calculations of the object’s

dimensions. For liquid materials, volume can be determined by determining the volume of the

container the liquid occupies. Most common laboratory glassware like beakers, Erlenmeyer flasks,

and test tubes serve as containers for mixing, handling, and heating solutions but are not designed

for accurate volume determinations. Volumetric devices used for analytical measurements include

volumetric flask, volumetric pipets or transfer pipet, burets, micropipets, and syringes (Hage and

Carr 2011).

Calibration of volumetric devices is very important especially when the device is recently

acquired or when the device will be used at a temperature different from the temperature it was

initially calibrated. This is because glassware will contract or expand with a change in temperature.

In addition, water expands about 0.02% per degree around 20C (Christian 2004). Therefore, the

true volume is different from the volume that is read from the container. The true volume can be

achieved by calculation considering buoyancy effects and measuring the mass of water that is

contained by the volumetric device, and then calculating the volume of water that was present

using the known density of water at that temperature (Hage and Carr 2011).

Application

Practically this experiment must be done first, among all others. This is practically because it

main application is to ensure the accuracy of the volumetric glassware, that will be frequently used


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in the proceeding experiments. If this experiment gives out bad values, even though random and

systematically errors have been properly avoided and accounted for, chances are that the remaining

experiments that will follow onto this will definitely carry on this same type of error, an error that is

within the apparatus, not on the user itself.

IV. METHODOLOGY

Figure 2.1. Glassware and sample preparation

Glasswares were cleaned with detergent

and lots of tap water. They were then

rinsed with distilled water.

200-mL distilled water was placed in a

250-mL beaker and was allowed to

equilibrate in room temperature.

Distilled water bottle was allowed to

equilibrate to room temperature. It was

used for the calibration of the burette.


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A clean and dry Erlenmeyer flask with a

stopper was weighed in an analytical

balance. The weight was recorded.

Burette was filled with distilled water up

to the 0.00-mL mark. It was ensured that

no leakages or bubbles were found.

Initial volume was read to the nearest

0.01 using a meniscus reader.

About 10-mL of water was transferred

from the burette to the preweighed

Erlenmeyer flask. Delivered water =

apparent volume.

A stopper was put on the flask with

water. Mass was recorded. Step was

repeated until water in buret was

discarded until 50-mL mark carefully.

Differences in mass between two

consecutive mass weighings were taken

as water delivered.

Actual/ true volume was taken using:

Mass of H2O with buoyancy effect = mass

of H2O * buoyancy correction (eq. 1)

True volume = (corrected mass of

H2O)/(density of H2O at specified

temperature). (eq. 2)

Correction value for each apparent

volume was taken using:

Correction value = true volume –

apparent volume (eq. 3)

Entire procedure was repeated with 20

aliquots of water per delivery. Same was

done for 30-mL, 40-mL, and 50-mL

aliquots of water.

Values were plotted: correction values on

y-axis and apparent volume on x-axis.

Figure 2.2. Calibration of 50-mL buret


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Figure 2.3. Calibration of 25-mL and 10-mL pipets

For 25-mL pipet: A clean and dry 125-mL Erlenmeyer flask with stopper was weighed on an analytical balance.

Recorded as: initial mass.

For 10-mL pipet: A clean, dry 50‐mL beaker with parafilm was weighed on an

analytical balance. Recorded as: initial mass.

25-mL/10-mL water was transferred from

the pipet, allowing water to run out, with

the tip of the pipet touching the side of

the beaker. It was allowed 7-10 seconds

to drain. The mass of the beaker and

added water was recorded. Recorded:

water delivered = apparent volume.

This addition was repeated three more

times without discarding water in beaker

or flask. Recorded for every transfer:

apparent volume and mass of container

plus added water.

Difference in mass between each set of

two consecutive mass measurements

were obtained to determine mass of

water delivered in each trial.

Get true volume using eq. 1

Do entire procedure using 10-mL pipet.

The following were calculated for

calibrated pipets: a. the mean volume, b.

standard deviation, c. relative standard

deviation (%RSD), d. 95% confidence

interval, e. % relative error (theoretical

volume assumed was exactly 25-mL and

10-mL for pipets)


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V. DESCRIPTION OF THE APPARATUS / SET - UP

Figure 2.4. Volumetric flask. Figure 2.5. Volumetric pipet

Figure 2.6. Burette (buret)

A volumetric flask is an instrument that is used to contain an accurate amount of liquid. A

typical volumetric flask that is used in our laboratory measures 500 mL of liquid, which has a


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tolerance of ±0.2 mL. This tolerance equates to a relative uncertainty of about 400 ppm (parts per

million).

A volumetric pipet is an instrument that is used to transfer accurate amounts of liquid. There

are many types of volumetric pipets, among which are used in this laboratory where the 10-mL and

the 25-mL ones. The volumetric pipet has only one graduation, and in doing so it can only deliver

one accurate measure at a time.

A burette is a laboratory apparatus that is mainly used for quantitative chemical analyses of

liquids. It consists of a long, graduated glass tube with a stopcock (in a liquid burette’s case, on the

bottom) that is handled by a burette clamp, which is connected to an iron stand. The volume that

the burette dispenses is controlled by the stopcock, and is accurately measured by the graduations

of the glass tube.

VI. DATA SHEET

I. GLASSWARE AND SAMPLE PREPARATION

Table 1. Water temperature

Container Temperature (C)

250 mL beaker 24C

Distilled water bottle 24C


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II. CALIBRATION OF 50 mL BURET

Table 2. Calibration of 50 mL buret

Conditions Trial 1 Trial 2

Mass of Erlenmeyer flask, g 113.79 117.52

10-mL delivery (1st)

Final volume, mL 9.9 10.0

Initial volume, mL 0.00 0.00

Volume used, mL 9.9 10.0

Mass of flask + 10 mL water, g 123.19 127.57

Mass of water, g 9.41 10.05

10-mL delivery (2nd)






10-mL delivery (3rd)






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10-mL delivery (4th)


Initial volume, mL 30,0 30.0



















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Table 3. Volumes for the 50 mL Buret

Conditions Trial 1 Trial 2


Apparent volume , mL 9.9 10


Corrected mass, g 9.41 10.07

True volume, mL 9.44 10.10

Correction value, mL -0.46 0.10


Apparent volume , mL 10.1 10



True volume, mL 10,17 10.06

Correction value, mL 0.07 0.06

10-mL delivery (3rd)


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Apparent volume , mL 10 10




Correction value, mL 0 0


Apparent volume , mL 10 10.1

Mass of water, g 10 10.07





Apparent volume , mL 10 9.9






Apparent volume , mL 19.9 20.0




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Correction value, mL 0.03 -0.08





















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Correction value, mL -0.10 0.15

III. CALIBRATION OF 25 mL AND 10 mL VOLUMETRIC PIPET

Table 4. Calibration of 25 mL volumetric pipet and 10 mL measuring pipet

Conditions 25-mL pipet Conditions 10-mL pipet

Mass of Erlenmeyer

flask, g 117.52 Mass of beaker, g

30.45

25-mL delivery

(1st trial)

10-mL delivery (1st

trial)

Volume delivered, mL 25.0 Volume delivered, mL 10.0

Mass of flask + 25 mL

water, g 142.45

Mass of beaker + 10

mL water, g

40.35

Mass of water, g 24.93 Mass of water, g 9.9

Corrected mass, g 25.02 Corrected mass, g 9.91

True volume, mL 25.04 True volume, mL 9.94

25-mL delivery

(2nd trial)

10-mL delivery (2nd

trial)



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water, g 167.33

Mass of beaker + 10

mL water, g

30.29




25-mL delivery

(3rdtrial )

10-mL delivery

(3rdtrial)



water, g 192.21

Mass of beaker + 10

mL water, g

60.28




Statistical Analysis

Average volume 25.01 Average volume 9.96

Standard deviation 0.029 Standard deviation 0.05

RSD 0.12% RSD 0.54%

95% confidence

interval 25.01±0.028

95% confidence

interval

9.96±0.049

% relative error 0.04% % relative error 0.4%


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VII. SAMPLE CALCULATIONS

For Table 3

( )( )

VIII. RESULTS AND DISCUSSIONS

This experiment is all about calibration of laboratory glassware. Calibration is very much

needed for the instruments, since it is one of the primary processes used in maintaining the

instrument’s measuring accuracy. Calibration, hence, means the process of configuring an

instrument (and accepting whatever environmental factors might be affecting it, even in a

controlled laboratory setting) to provide certain results from a sample within an acceptable range

(which is known as the tolerance). The table showing the tolerances of common Class A glassware is

shown.

Table 1. Tolerance for Class A Laboratory Glassware*

Tolerance of Class A burets Tolerance of Class A transfer pipets

Buret volume (mL)

Smallest Graduation (mL)

Tolerance ((mL)

Volume (mL) Tolerance (mL)

50 0.1 ±0.05 10 ±0.02

25 ±0.03

*Quantitative Chemical Analysis (6th ed). NY: W.H.Freeman and Company.

This is done to minimize or readily eliminate the inaccurate measurements that can be done by

the instrument, and is one of the instrumentation design’s fundamental aspects. With this done, an

instrument that has assigned its proper measurement can now be called a standard. Also,

calibration is done when the environment’s temperature setting is not in tune with the one from

which the instrument was originally made, or formerly calibrated, since density and buoyancy

factors change the slightest of a single measurement, even though the estimated significance of the


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measurement is certain (because you are using a graduated measuring instrument). The table

showing the corrections of density and buoyancy correction is shown below.

Table 2. Density of Water at Various Temperatures**

Temperature (C) Density (g/cm3) Buoyancy correction

10 0.9997026 mdisplay ∙ 1.00152

11 0.9996084 mdisplay ∙ 1.00152

12 0.9995004 mdisplay ∙ 1.00152

13 0.9993801 mdisplay ∙ 1.00152

14 0.9992744 mdisplay ∙ 1.00152

15 0.9991026 mdisplay ∙ 1.00152

16 0.9989460 mdisplay ∙ 1.00152

17 0.9987779 mdisplay ∙ 1.00153

18 0.9985986 mdisplay ∙ 1.00153

19 0.9984082 mdisplay ∙ 1.00153

20 0.9982071 mdisplay ∙ 1.00153

21 0.9979955 mdisplay ∙ 1.00153

22 0.9977735 mdisplay ∙ 1.00154

23 0.9975415 mdisplay ∙ 1.00154

24 0.9972995 mdisplay ∙ 1.00154

25 0.9970479 mdisplay ∙ 1.00155

26 0.9967867 mdisplay ∙ 1.00155

27 0.9965162 mdisplay ∙ 1.00155

28 0.9962365 mdisplay ∙ 1.00156

29 0.9959478 mdisplay ∙ 1.00156

30 0.9956502 mdisplay ∙ 1.00156

** All of the densities shown for pure air-free water at a pressure of 101.325 kPa (1 atm). The

buoyancy corrections assume that the air density is 1.20 x 10-3 g/cm3 and the density of the reference

weight is 8.00 g/cm3.

** Analytical Chemistry and Quantitative Analysis. New Jersey: Pearson Prentice Hall.

We started the experiment off by thoroughly cleaning the glassware. They are clean as it

seems, but maybe the students that used it before us didn’t thoroughly clean it through, so we have

to do it again for assurance that the calibration will be very much accurate. The final rinsing will be


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the distilled water, which is free of most ions present in tap water, and in effect the water will not

be attracted to the sides of the glassware, creating a free flowing liquid inside. Since the distilled

water that we used in the wash bottle already equilibrated to room temperature, we just read this

temperature which will be used for computations later on.

We started calibrating the 50-mL buret by filling the buret with distilled water. Then, by getting

the mass of the Erlenmeyer flask (which will be used throughout this whole procedure) we now

transfer an appropriate amount (10-ml aliquots, adding 10 to the preceding one until we have 50-

mL aliquots, for two trials) to the flask and weigh the flask. The difference between the last reading

and the initial will be the mass of the water. After all trials and different aliquots have been done,

we go to the computation step. By having the apparent mass of the water, we now compute for the

corrected mass of water by the equation:

( )( ). (Eq 1)

By getting the mass, we can get the corrected/true volume by the equation:

. (Eq 2)

By having the true volume, we compute for the correction value as follows:

. (Eq 3)

After this, we will graph the correction values vs. apparent volume. By inspection, you can see

that there are negative and positive values for the correction value. This is mainly because of the

difference in the mass weighed to the volume that you have estimated to the burette’s significant

figures (even with the help of the meniscus reader). The slope of the line will serve as the relative

error of the calibration process, and if it goes by the specific tolerance, then the glassware has been

properly calibrated.

For the calibration of the 10-mL and 25-mL pipet, a proper container for delivery is allocated

for the different measuring instruments. A 125-mL E. flask is used for the 25-mL pipet and a 50-mL

beaker with parafilm for the 10-mL pipet. By getting the respective weights of the containers, for

three trials we transferred distilled water to its appropriate container, and weighing it to get the

difference, which will serve as the apparent mass of water. After all trials have been made, the

computation process will be the same as the 50-mL buret computations, i.e. getting the correction


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value. After this has been made, the data that we have computed and determined will be compared

using statistical analysis. By getting the means of the true volumes of the different pipets, we

computed for the standard deviation by the equation:

√∑( ̅)

. (Eq 4)

After that, we computed for the coefficient of variation (%relative standard deviation) to see

how precise our measurements are. We got a low value; therefore our precision is very high. Also,

the %RSD can be used as comparison for the tolerances that is in Table 1. From what we got, we are

inside the bounds of the tolerance values, therefore the values are within range. By getting the

confidence interval, we computed for its actual tolerances, assuming that this is the working

temperature for this glassware throughout the whole term. Lastly, we determined the %relative

error, using 25-mL and 10-mL measurements as the theoretical volume. This can be compared to

the tolerances, and from what we got, we are within range.

0.1

0.06

0

y = 2x - 19.92

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

9.94 9.96 9.98 10 10.02

10-mL aliquots (Correction values vs. Apparent volume)

Correction values

Linear (Correctionvalues)


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By cleaning up everything and putting everything to what it was back before, we conclude the

experiment to a finish.

IX. SUMMARY AND CONCLUSIONS

This experiment verified the concept involving the how to’s of calibrating glassware, such as

burettes and volumetric flasks. The glasswares were already previously calibrated during

manufacture by the Quality Control (QC) department, but calibrating the instruments would be

needed to ensure that no errors have been made by the QC, if ever. Even in a controlled laboratory

setting, a random error can always happen.

Certain factors that can affect the precision and accuracy of measurements of these glasswares

are quite a few. Linear expansion would b a thing, but since the difference in the temperature in the

laboratory would be very low, this can be way much disregarded. A difference in temperature, from

what is said earlier, however, can affect the density of the liquid being contained or transferred.

Density is the mass to volume ratio of a substance i.e. liquid, which is significant since for every

degree of change, there would be a notable difference in the density. This is because the mass of

0.03

0.09

-0.03

y = 0.3x - 5.97

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

19.85 19.9 19.95 20 20.05 20.1 20.15

20-mL aliquots (Correction values vs. Apparent volume)

Correction values

Linear (Correctionvalues)


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the water is affected by buoyancy. With this changes, plus environmental factors, will cause a

significant change between the volume obtained, and the true volume.

Overall, by getting the relative difference through statistical methods and comparing it to the

standard values (with the tolerance values as a guide for maximum allowable error), if it is within

the bounds, then we can conclude that the glassware are calibrated to accuracy, and can be used for

future purposes.

X. POST LAB QUESTIONS

1. What is the maximum allowable error for the respective volumetric glassware that you

calibrated?

Based on our data, the maximum allowable error is about 0.41%, since the average tells this

much difference, as to the computation o the relative error.

2. Are your errors within the tolerance volumes for the Class A glassware? What are the

systematic or random errors that have occurred?

Yes. If there are errors, what have possibly occurred would be: the reading of the lower

meniscus, which always results to estimation; and possibly the water drops left inside the

glassware due to the surface tension inside.

XI. REFERENCES

Christian, Gary D. 2004. Analytical chemistry (6th ed.). John Wiley and Sons Inc.

Hage, David S. and James D. Carr. 2011. Analytical chemistry and quantitative analysis. New

Jersey: Pearson Prentice Hall.

Skoog, Douglas et. al. 2004. Fundamentals of Analytical Chemistry (8th ed.). Singapore:

Thomson Learning.

Experiment 2 - Calibration of Volumetric Glassware

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