physical chem

FACULTY OF RESOURCE SCIENCE AND TECHNOLOGY DEPARTMENT OF CHEMISTRY

STK 1201 –Practical Physical Chemistry 1

EXPERIMENT NO: 4

TITLE OF EXPERIMENT : CALORIMETRY

DATE OF EXPERIMENT : 27.10.2015

GROUP MEMBERS & MATRICS NUMBER

: MANJUBASINY A/P SEZHIAN (54717) NURUL AMRINA BINTI MASANI (54938)

LAB FACILITATOR :GROUP NUMBER : 27

DUE DATE : 17.11.2015

INTRODUCTION

Volumetric glassware is generally made to specification limits, particularly with regards to the accuracy of calibration. While every effort will have been made in the construction of the glassware to ensure that it is accurate and within its specified tolerance, it is possible that they may require calibration. Calibration of laboratory glasswares can be carried out with the use of distilled water, and an accurate balance. Using the known density of water, the volume contained in or delivered by a piece of glassware may be accurately determined using equation (1.1).

ρ = m/V ----- (1.1)

Volumetric flask

Volumetric flasks are calibrated to contain an exact volume of solution when the solution level is exactly at the mark on the neck of flask (the bottom of the meniscus should lie exactly at this mark).

Pipette

Pipettes are calibrated to deliver an exact volume of liquid or solution. There are two types of pipettes: volumetric pipette and Mohr pipette. Volumetric pipettes have only one calibration mark. Mohr pipettes, which are sometimes known as graduated pipettes, are used to deliver fractional volumes of solution. These pipettes have graduated marks throughout the length of the pipettes, therefore they are far less accurate than volumetric pipettes. To fill a pipette, one simply draw in liquid to the mark. Usually it is easiest to initially overshoot the mark and then let the liquid drain from the pipettes until the bottom of the meniscus lies exactly on the calibration mark.

Burette

Burettes allow you to accurately deliver volumes of liquid that cannot be measured by volumetric pipettes or micropipettors. The proper use of burettes is essential for accurate titration analyses.

The objective of this experiment is to determine the accuracy and precision of some commonly used glassware. In this exercise you will calibrate a volumetric pipette, a burette and a volumetric flask.

MATERIAL AND APPARATUS

Reagent

1. Distilled water

Apparatus

1. Volumetric pipette 2. Burette 3. Beaker 4. Volumetric flask

METHODOLOGY

A) Pipette Calibration

1. A volumetric pipette was selected to calibrate.2. A small empty beaker was placed on the analytical balance and tare the balance.3. The pipette was filled to the calibration mark with distilled water and the water drained

into the beaker on the balance. A small amount of solution remained in the pipette. That was not blown out. The mass of water transferred was recorded.

4. The balance was tarred and this procedure was repeated twice.5. The water volumes from the masses recorded was calculated.

B) Burette Calibration

1. The burette was filled with distilled water and any air bubbles are forced out of the tip. The burette was drained without leaving drops on the walls. The burette was cleaned with distilled water and the burette were touched at the tip to a beaker to remove the suspended drop of water. The burette was allowed to stand for 5 minutes. The stopcock are tightened when the level of the liquid in the burette has changed and the procedure was repeated. the initial reading was recorded.

2. A clean and dry Erlenmeyer flask was weighed and the mass was recorded to the nearest 0.0001g.

3. 5 mL of distilled water are drained into Erlenmeyer flask. The film of liquid on the walls are allowed to descend for about 30 seconds before the reading of the burette are recorded.

4. The flask was weighed again to determine the mass of water delivered.5. The process was repeated 2 more times.6. The procedure for 10mL, 15mL, 20mL and 25 mL are repeated.7. The density information are used to determine the true volume of water delivered.

C) Volumetric Flask Calibration

1. A dry and clean volumetric flask was selected to calibrate.2. The mass of the empty, dry volumetric flask with stopper was recorded.

3. The volumetric flask was filled ot the mark with distilled water and the mass was recorded.

4. The procedure was repeated twice and the actual volume of distilled water contained was calculated.

RESULTS

A) Pipette Calibration

Trial 1 Trial 2 Trial 3Water temperature, t (C) 28.0 28.0 28.0Mass of empty beaker (g) 47.72 47.70 47.72Mass of beaker with distilled water (g) 72.51 72.29 72.49Apparent mass of water transferred (g) 24.79 24.59 24.77True mass of water transferred (g)Apparent mass refers to the measurement under vacuum condition. The density of air is 0.0012 g/mL. Therefore, the mass of air displaced in the water transferred is 0.0012 times the volume of water transferred. The calculated mass of air displaced has to be added to the apparent mass to give true mass of water.

24.82 24.62 24.80

Density of water at t C (g/mL) 0.996232 0.996232 0.996232Actual volume of water transferred (mL) 24.91 24.71 24.89Average volume of water transferred (mL) + standard deviation

24.84±0.01 24.84±0.01 24.84±0.01

B) Burette Calibration

5ml Trial 1 Trial 2 Trial 3Water temperature, t (C) 28.0 28.0 28.0Initial reading of burette (to 0.01 mL) 0.00 5.00 10.00Final reading of burette (to 0.01mL) 5.00 10.00 15.00Nominal volume of water transferred (mL) 5.00 5.00 5.00Mass of empty Erlenmeyer flask (g) 52.360 52.362 52.671Mass of Erlenmeyer flask with water(g) 57.345 57.348 57.352Apparent mass of water (g) 4.985 4.886 4.681True mass of water (g) 4.991 4.892 4.687Density of water at tC (g/mL) 0.996232 0.996232 0.996232Actual volume of water transferred (mL) 5.010 4.911 4.705Correction of nominal (labelled) volume (mL) 5.019 5.019 5.019Average volume of water transferred (mL) ± standard deviation

4.875±0.01 4.875±0.01 4.875±0.01


10.148±0.01 10.148±0.01 10.148±0.01


15.347±0.01 15.347±0.01 15.347±0.01

20ml Trial 1 Trial 2 Trial 3Water temperature, t (C) 28.0 28.0 28.0Initial reading of burette (to 0.01 mL) 0.00 0.00 0.00Final reading of burette (to 0.01mL) 20.00 20.00 20.00

Nominal volume of water transferred (mL) 20.00 20.00 20.00Mass of empty Erlenmeyer flask (g) 52.381 52.382 52.381Mass of Erlenmeyer flask with water(g) 72.421 72.430 72.423Apparent mass of water (g) 20.040 20.048 20.042True mass of water (g) 20.064 20.072 20.066Density of water at tC (g/mL) 0.996232 0.996232 0.996232Actual volume of water transferred (mL) 20.140 20.148 20.142Correction of nominal (labelled) volume (mL) 20.076 20.076 20.076Average volume of water transferred (mL) ± standard deviation

20.143±0.01 20.143±0.01 20.143±0.01


25.416±0.01 25.416±0.01 25.416±0.01

C) Volumetric Flask Calibration

Trial 1 Trial 2 Trial 3Water temperature, t (C) 28.0 28.0 28.0Mass of empty volumetric flask (g) 49.356 49.359 49.360Mass of volumetric flask with distilled water (g)

148.749 148.575 148.592

Apparent mass of water transferred (g) 99.393 99.216 99.232True mass of water transferred (g) 99.512 99.335 99.551Density of water at t C (g/mL) 0.996232 0.996232 0.996232Actual volume of water transferred (mL) 99.888 99.711 99.727Average volume of water transferred (mL) + standard deviation

99.775±0.01 99.775±0.01 99.775±0.01

CALCULATIONS

Pipette calibrations: Apparent mass of water = Mass of beaker with - Mass of empty beaker (g)

transferred (g) distilled water (g)

Trial 1 : apparent mass of water (g) = 72.51 – 47.72 = 24.79g

Trial 2 : apparent mass of water (g) = 72.29-47.70 = 24.59g


True mass of water transferred =(0.0012g/mL×volume of water transferred) + apparent mass of water

Trial 1 : true mass of water transferred (g) = (0.0012 × 24.79)+24.79 = 24.82g

Trial 2 : : true mass of water transferred (g) = (0.0012 × 24.59)+24.59 = 24.62g

Trial 3 : : true mass of water transferred (g) = (0.0012 × 24.77)+24.77 = 24.84g

Actual volume of water transferred = massof water transferred , gdensity of water at t , °C

Trial 1 : actual volume of water transferred = 24.82

0.996232 = 24.91 mL


0.996232 = 24.71 mL


0.996232 = 24.89 mL

Average volume of water transferred = (24.91+24.71+24.89)/3

(mL) ± standard deviation = (24.84 ± 0.01) mL

Burette calibrations: The calculation method is same for 10mL,15mL,20mL and 25mL. Below calculation is by using 5mL.

Apparent mass of water = Mass of Erlenmeyer - Mass of empty Erlenmeyertransferred (g) flask with distilled flask (g) water (g)





Trial 1 : true mass of water transferred (g) = (0.0012 × 4.985)+ 4.985 = 4.991g





0.996232 = 5.010 mL


0.996232 = 4.911mL


0.996232 = 4.705 mL

Correction of nominal = Nominal volume of water transferred ,mLDensity of water transferred at t °C ,g /mL

(labelled) volume (mL)

Trial 1 : correction of nominal (labelled) volume = 5.00

0.996232 = 5.019 mL

*the value for trial 2 and trial 3 is equal to the value of trial 1

Average volume of water transferred = (5.010+4.911+4.705)/3(mL) ± standard deviation = (4.875 ± 0.001) mL

Volumetric flask calibrations:

Apparent mass of water = Mass of volumetric - Mass of empty volumetrictransferred (g) flask with distilled flask (g) water (g)


Trial 2 : apparent mass of water (g) =148.575-49.359 = 99.216g

Trial 3 : apparent mass of water (g) = 148.592-49.360

= 99.232g







0.996232 = 99.888 mL


0.996232 = 99.711 mL


0.996232 = 99.727mL

Average volume of water transferred =( 99.888+99.711+99.727)/3

(mL) ± standard deviation

= (99.775± 0.001) mL

DISCUSSION

In this experiment, we are required to test the accuracy and precision of some commonly used glassware. All the used glassware were not precise in the experiment conducted, for precision is the repeatability or reproducibility of measured values of the same quantity. This evidence is found in all the results of the used glassware , example are some of the values were not repeated twice in the data collected during the experiment. However, the data of the experiment were not accurate because non had a range equal to or above the true value of the volumetric glassware standardized.

CONCLUSION

Overall, by getting the relative difference through statistical methods by comparing it to the standard values, if it is within the bounds, then we can conclude that the glassware are calibrated to accuracy.

In conclusion, the volume of the various standardized glassware was not accurate, this to tell us that glassware in the laboratory may not accurately contain the volume prescribe on them unless the temperature and density of the substance are noted.

POST-LAB QUESTIONS

1. Pipettes are used to transfer liquid sample and they are rinsed with small amount of the

sample after transfer. Calculate the % error that will be produced with pipette of 1mL,

5mL, and 10mL if each pipette retains 5 drops of water after use. Assuming the volume

of one drop of water is 0.05mL.

i. For 1mL of pipette: The percentage error, % = (0.05×5)

1.0 × 100%

= 25%

ii. For 5 mL of pipette: The percentage error, % = (0.05×5)

5.0 × 100%

= 5%

iii. For 10 mL of pipette: The percentage error, % = (0.05×5)

10.0 × 100%

= 2.5%

2. It is important to ensure that no air bubbles are captured at the stopcock of the burette

when the initial reading is recorded. If 0.5 mL of air bubbles is present in the burette,

what is the % error that will be generated in 10 mL, 20 mL, and 40 mL of the sample

when the air bubbles are released?

a) For 10 mL: The percentage error, % = 0.5

10.0 100%

= 5%

b) For 20 mL: The percentage error, % = 0.5

20.0 100%

= 2.5%

c) For 40 mL: The percentage error, % = 0.5

40.0 100%

= 1.25%

REFERENCE

1. Shoemaker.P.David, Garland.W.Carl, Nibler.W Joseph, (1989), Experiments in Physical

Chemistry, 5th Edition, Mc.Graw.Hill,Inc.

2. To calculate percentage error can be get through this link:

http://staff.bhusd.org/bhhs/cbushee/Current/PercentError.htm ( Accessed on 12/10/2015).

Documents

physical chem