MOLAR MASS OF A VOLATILE LIQUID

CHEMISTRY LAB REPORT

October 4 th , 2009

LAB PERFORMED BY:Narendran Sairam and Steven Kraplin

Table Of Contents

Objective .......................................................................................................................................3 Equipment......................................................................................................................................3 Experimental Procedure.................................................................................................................3 Observations...................................................................................................................................4 Data Table......................................................................................................................................4 Calculations...................................................................................................................................5 Conclusion.....................................................................................................................................5

Objective

The Objective of this lab is to experimentally determine the molar mass of an unknown and

volatile liquid.

Equipment

Hot Plate

200 mL Flat Bottom Flask

1000 mL Beaker

600 mL Beaker

Flask Clip

Flask Cap

Cork

Ring Stand

25 ml Graduated Cylinder

Funnel

Buret Clamp

5.1 mL of Unknown A

Thermometer

Experimental Procedure

1. All essential equipment was obtained from instructor.

2. 5.1 ml of Unknown A liquid was measured in a 25ml volumetric flask.

3. The ring stand was setup and the hot plate was placed on the base of the stand.

4. The empty flat bottom flask was weighed and then the unknown liquid was poured into it.

5. The 1 liter beaker was placed on the hot plate and filled with enough water to submerge the flat

bottom flask.

6. Supported by a buret clap attached to the ring stand, the flat bottom flask was lowered into the

beaker.

7. The thermometer was also lowered into the beaker.

8. Initially a cork was used to seal the cap of the flask, but then, owing to new instructions, the use

of the cork was abandoned.

9. The beaker was heated on the hot plate until the liquid in the flask evaporated.

10. After the liquid evaporated, the water in the beaker was allowed to boil for an additional 5-8

minutes before the hot plate was turned off.

11. The flask was removed from the beaker and a cork was used to seal the cap.

12. The flask was then lowered into a beaker of cold water and allowed to completely cool.

13. The barometric pressure was observed and recorded.

14. The flask was weighed with the condensed liquid in it.

15. The temperature of the water in the 1 liter beaker was observed through out the experiment.

Observations

During step 9, as the water was being heated, the unknown liquid began boiling at 72°C and a

vapor began rising from the flask at about 85°C.

The water in the 1 liter beaker began boiling violently at 100°C.

At about 90°C the unknown liquid evaporated completely leaving a yellow residue behind.

After step 12, the vapor in the flask condensed to form a liquid.

Data Table

Measurement Value

Mass of flask and stopper 123.56 g

Mass of flask, stopper, and condensed vapor

124.4 g

Temperature of boiling water bath 98.8˚C

Barometric pressure 740 mm Hg

Calculations

Measurement Value

Pressure of vapor, P 0.9736842105 atm

Volume of flask (volume of vapor), V 0.2866 L

Gas Constant, R 0.0821 L atm/(mole K)

Temperature of vapor, T 371.95˚K

Mass of vapor, g 0.84 g

Number of moles of vapor, n 0.0091383249 M

Molar mass of unknown 91.92056661 g

Conclusion

The expected molar mass of the given liquid was 88g but the molar mass obtained through the

experimentation was 91.92056661 g. This discrepancy is most probably a result of mechanical errors

such as inaccurate mass provided by the weighing scales, incorrect pressure provided by barometer or

inaccurate results of calculations provided by our calculator.