The purpose of this experiment is to study the relationship of several types of volumetric glassware and the accuracy of measuring the volumes of liquids very precisely in quantitative laboratory work. The accuracy of the measurement the volumes is the degree of closeness of measurements of a quantity’s actual volumes while the precision of the volumes is the degree to which repeated measurements under unchanged conditions show the same results.

Each of volumetric glassware is marked with its total volume, the notation of TD for ‘to deliver’ and TC for ‘to contain’ and also with the temperature at which the calibration applies. For greatest accuracy, volumetric glassware should be calibrated to measure the volume that is actually contained in or delivered by a particular piece of glassware.

The calibration is done by measuring the mass of water contained in or delivered by the glassware. The density of water at a particular temperature is used to convert mass into volume. Pipettes and burettes are calibrated to deliver specific volumes whereas, volumetric flasks are calibrated to contain basis.

MATERIAL AND PROCEDURE

The materials used in the experiment were:-

10 mL volumetric pipette

25 mL volumetric pipette

100 mL volumetric flask

50 mL measuring cylinder

Distilled water

Plastic dropper

100 mL beaker

250 mL beaker

The procedure

1. Calibration of a volumetric pipette ( 10 mL and 25 mL )

a) An empty 100ml beaker was weighed to the nearest milligram using electronic weigh balance. b) The 10ml pipette was filled to the mark with distilled water. c) The water was drained by gravity (remove pipette bulb or pump) into the beaker and caps the bottle to prevent evaporation. d) The bottle was weighed again to find the mass of water delivered from the pipette. e) Then used the following equation to convert mass to volume. f) The above procedure was performed on each of the pipette. g) The experiment was repeated for 2 times.

True (actual) Volume = (grams of water) x (volume of 1 g of H20 in Table 1

2. Calibration of a volumetric flask (100ml)

a) An empty 100ml volumetric flask was weighed to the nearest milligram using electronic weigh balance. b) The flask was filled to the mark with distilled water and weighed again. c) The mass of water contained in the flask was calculated.

d) Then convert the mass of water to volume.

e) The procedure was repeated two times again.

3. Calibration of a measuring cylinder

a) An empty 50ml measuring cylinder was weighed to the nearest milligram using electronic weigh balance. b) The measuring cylinder was filled to the mark with distilled water and weighed again. c) The mass of water contained in measuring cylinder was calculated. d) Then convert the mass of water to volume by the procedure you think most appropriate. e) Repeat the experiment for two times.

RESULTS AND DISCUSSION

I. 10mL pipette

Trial 1

Trial 2

Trial 3

Mass of container + water (g)

59.31

59.34

59.28

Mass of container (g)

49.55

49.56

49.54

Mass of water (g)

9.76

9.78

9.74

Temperature (°C)

32

32

32

Actual volume (mL)

9.82

9.84

9.80

Average volume (mL)

9.82

Standard deviation, σ

0.02

Relative standard deviation (σ/

2.036666×10-3

II. 25ml pipette

Trial 1

Trial 2

Trial 3

Mass of container + water (g)

74.06

74.04

74.25

Mass of container (g)

49.56

49.55

49.54

Mass of water (g)

24.50

24.49

24.71

Temperature (°C)

32

32

32

Actual volume (mL)

24.64

24.63

24.85

Average volume (mL)

24.71

Standard deviation, σ

0.1243

Relative standard deviation (σ/

5.0304 × 10-3

III. 100mL volumetric flask

Trial 1

Trial 2

Trial 3

Mass of container + water (g)

165.61

165.57

165.70

Mass of container (g)

66.74

66.75

66.77

Mass of water (g)

98.87

98.82

98.93

Temperature (°C)

32

32

32

Actual volume (mL)

99.44

99.39

99.50

Average volume (mL)

99.44

Standard deviation, σ

0.0552

Relative standard deviation (σ/

5.55 × 10-3

IV. 50mL measuring cylinder

Trial 1

Trial 2

Trial 3

Mass of container + water (g)

116.80

116.78

116.73

Mass of container (g)

67.57

67.76

67.78

Mass of water (g)

49.05

49.02

48.95

Temperature (°C)

32

32

32

Actual volume (mL)

49.34

49.30

49.23

Average volume (mL)

49.29

Standard deviation, σ

0.055678

Relative standard deviation (σ/

1.1296 × 10-3

DISCUSSION

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 or delivered by the glassware. The density of water at a particular temperature which is measured is used to convert mass into volume. Pipettes is calibrated to deliver specific volumes whereas volumetric flasks are calibrated on a contain basis. BRIEF THEORY:

In this experiment, we were exposed to a variety of important concepts related to quantitative experimentation, including the proper use of measuring cylinder, volumetric glassware, analytical balances and statistics. We calibrated a volumetric pipette that was where experimentally determined what volume a pipette or flask really delivers. We also calibrated a beaker and 50 mL burette.

A table was constructed according to the result. In this experiment, accuracy and precision is important. The brief theory of calibration of glassware is accuracy and precision. Accuracy is the degree of closeness of measurements of a quantity’s actual volumes while the precision of the volumes is the degree to which repeated measurements under unchanged conditions show the same results.

For the accuracy and precision of the measurement, scientists need to calibrate their volumetric glassware periodically. Calibration of Volumetric Glassware experiment is designed to help participants to learn both theories and practical skills to effectively calibrate and verify their volumetric glassware. The mass of water, container and temperature is measured and recorded. From the data recorded, we can observe that all the experiment results are not in accurate and stable.

For the 10ml pipet experiment, the result is increase from Trial 1 to Trial 2 but decrease from Trial 2 to Trial 3. Then for the 25ml pipet experiment, the result is decrease from Trial 1 to Trial 2 but from Trial 2 to Trial 3, the result is increase. After that, for 100ml volumetric flask the result is decrease from Trial 1 to Trial 2 but increase from Trial 2 to Trial 3. For 50ml measuring cylinder, the result is decrease from Trial 1 to Trial

3. When the results are compared to the theory, we can conclude that our result for experiment is not accurate but precise. It is not accurate because of the different pressure from surrounding. But then, the results are precise because all the measurement recorded shows the same results. From this experiment, there are possible error occur. Firstly, error occurs during measure on electronic weigh balance. Second, the apparatus is not dry and cleaned in a proper way. Third, parallax error occurs during measure the apparatus.

CONCLUSION

In conclusion, this experiment is conducted to investigate how to calibrate the liquid accurately and precisely by using volumetric glassware. In order to study the problem, we did three complete trials for each of the calibration of volumetric glassware. My results showed that the trial with the highest relative standard deviation was 100 mL volumetric glassware while the lowest greatest relative standard deviation was 50 mL measuring cylinder.

This can conclude that the accuracy of the volumetric glassware is affected by the sensitivity of the instruments. In order to overcome the error, we have to make sure that the eye position is perpendicular to the reading scale of the apparatus to avoid parallax error. Besides that, the beaker should be clean and dry properly so that there is no water left which can affect the mass of the next trial. Apart from that, the volumetric glassware should be weight properly in order to get the accurate and precise results.

APPENDIX

Questions

1. Please tell in simplest way what calibration is…..

Calibration is a comparison between measurements which is known as magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device. 2. Draw a flowchart for the calibration of 50 mL measuring cylinder.

3. With the reference to the capacity of the glassware you have chosen, give a set of reading to illustrate the meaning of good accuracy and poor precision.

With reference to the capacity of the glassware you have chosen, give asset of reading to illustrate the meaning of good accuracy and poor precision. Accuracy is how close the measurement is to the actual measurement. Good accuracy and poor precision means the readings of the measurements are not particularly close to each other but the readings are close to the actual reading of the glassware chosen. Example:

The capacity of the measuring cylinder is 50mL.

The measurements taken: 48.8mL, 50.1mL, 49.6mL, 47.4mL, 50mL, 50.2mL. This distribution shows no impressive tendency toward a particular value (lack of precision) but each value does come close to the actual volume (high accuracy).

4. What does standard deviation, σ, indicate?

The standard deviation is a measure that summaries the amount by which every value within a dataset varies from the mean. Effectively it indicates how tightly the values in the dataset are bunched around the mean value. It is the most robust and widely used measure of dispersion since, unlike the range and inter-quartile range; it takes into account every variable in the dataset. When the values in a dataset are pretty tightly bunched together the standard deviation is small. When the values are spread apart the standard deviation will be relatively large.

The standard deviation is usually presented in conjunction with the mean and is measured in the same units. Standard deviation is calculated as square root of variance. In many datasets the values deviate from the mean value due to chance and such datasets are said to display a normal distribution. In a dataset with a normal distribution most of the values are clustered around the mean while relatively few values tend to be extremely high or extremely low. Many natural phenomena display a normal distribution.

5. A 50 mL pipette delivers 49.960 g of water at 27 ̊C. calculate the volume delivered by this pipette at 28 ̊C. (Given 1.000 g of water weight in air occupies 1.0048 mL at 28 ̊C)

27 ºC = 49.960g

Grams of water at 1 ºC = (49.960g x 1 ºC)/ 27ºC

= 1.8504 g

1 ºC = 1.8504 g

Grams of water at 28 ºC = (1.8504g x 28 ºC)/1 ºC

= 51.8104 g

Volume = 51.8104 g x 1.0048 mL

= 52.0591 g mL

Calculations

I. Standard Deviation , σ

(x1-x̑) 2+(x2-x̑) 2+(x3-x̑) 2]

(9.82-9.82)2+ (9.84-9.84)2+ (9.80-9.82)2]

(0+0.0004+0.0004]

=0.02

Relative standard deviation, (σ/ x̑)

= 0.02/9.82

= 2.03666×10-3

II. Standard Deviation, σ

(x1-x̑) 2+(x2-x̑) 2+(x3-x̑) 2]

(24.64-24.71)2+ (24.63-24.71)2+ (24.85-24.71)2]

(4.9×10-3)+ (6.4×10-3) + (0.0196)2]

0.0309]

= 0.1243

Relative standard deviation, (σ/ x̑)

= 0.1243/24.71

= 5.0×10-3

III. Standard Deviation , σ

(x1-x̑) 2+(x2-x̑) 2+(x3-x̑) 2]

(99.44-99.44)2+ (99.39-99.44)2+ (99.50-99.44)2]

0+ (2.5×10-3) + (3.6×10-3)]

6.1×10-3]

3.05×10-3

= 0.0552

Relative standard deviation, (σ/ x̑)

=0.0552/99.44

=5.55×10-3

IV. Standard Deviation , σ

(x1-x̑) 2+(x2-x̑) 2+(x3-x̑) 2]

(49.34-49.29)2+ (49.30-49.29)2+ (49.23-49.29)2]

(2.5×10-3)+ (1×10-4) + (3.6×10-3)]

6.2×10-3]

= 3.1×10-3]

= 0.055678

Relative standard deviation, (σ/ x̑)

=0.055678/49.29

=1.1296×10-3

REFERENCE

Chemistry eleventh Edition book by Raymond Chang

Elementary Principles of Chemical Processes by Richard M. Felder (Author), Ronald W. Rousseau (Author) Longman Essential Chemistry by Yeap Tok Kheng

http://en.wikipedia.org/wiki/Standard_deviation

http://www.udel.edu/chem/analytical/c119/Lab_2.pdf

SUMMARY

The purpose of this experiment was to measure volume of liquid and compared the result with the reading for each trial of volumetric glassware. By using all types of volumetric glassware, an accurate and precise measurement can be achieved. We had done three trials to get the accurate data. All the empty glassware was weighed at first and pour using the distilled water with the same amount of liquid. With the specific amount, the calibration is done by measuring the mass of water contained in or delivered by the particular glassware.

Then, the density of water of particular temperature is used to convert mass into volume. . Based on the result, the average volume of calibration of 10 mL volumetric pipette is 9.82 mL. The average volume of calibration of 25 mL volumetric pipette is 24.71 mL. Then, the average volume of calibration of 100 mL of volumetric flask is 99.44 mL. So, the average volume of 50 mL measuring cylinder is 49.20 mL. Ours result verified that the mass of volumetric glassware has some effects with the condition of surrounding.

Meanwhile, there are some possible errors occurred during the experiment, thus the result was distracted. In order to overcome the error, we have to make sure that the eye position is perpendicular to the reading scale of the apparatus to avoid parallax error. Last but not least, the beaker should be clean and dry properly so that there is no water left which can affect the mass of the next trial.

Courtney from Study Moose

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