Purpose: The purpose of this lab is to determine the identity of an unknown liquid by measuring

It’s density and boiling point, and then comparing the results to the values for known

substances.

Data and Calculations: The experiment is divided into two parts (Part A and Part B). In the first

part of experiment, the density of unknown liquid is measured by measuring

volume using three glassware.

1. Graduated Cylinder

Trial 1 Trial 2 Trial 3

Volume of Liquid

(mL)

15.1 30.2 45.3

Mass empty Cylinder

(g)

64.2291 N/A N/A

Mass cylinder + liquid

(g)

76.4224 88.3407 100.5113

Mass liquid (g) 12.1933 24.1116 36.2822

Density of Liquid

(g/mL)

0.808 0.798 0.801

Initial volume of unknown liquid = 15.1 mL

Second volume of unknown liquid = 30.2 mL

Final volume of unknown liquid = 40.3 mL

Mass Liquid (g) = [(Mass cylinder + liquid) – (Mass empty cylinder)] (g)

Density = Mass/Volume (g/mL)

Trial 1: Density = 12.1933 g/15.1 mL

= 0.808 g/mL

Trial 2: Density = 24.1116 g/30.2 mL

= 0.798 g/mL

Trial 3: Density = 36.2822 g/45.3 mL

= 0.801 g/mL

Average value of Density = (0.808 g/mL + 0.798 g/mL + 0.801 g/mL)/3

= 0.802 g/mL

Observations:

The unknown liquid may evaporates if it is remain open so it may cause some uncertainty.

The unknown liquid have colorless and some identical odor characteristics.

2. Volumetric Pipette

Initial volume of unknown liquid = 10.01 mL

Second volume of unknown liquid = 20.01 mL

Final volume of unknown liquid = 30.02 mL

Trial 1 Trail 2 Trial 3

Volume of liquid

(mL)

10.01 20.01 30.02

Mass empty beaker

(g)

69.4449 N/A N/A

Mass beaker + liquid

(g)

77.4111 85.3162 93.1833

Mass liquid (g) 7.9662 15.8713 23.7384

Density of liquid

(g/mL)

0.7958 0.7932 0.7861

Mass liquid (g) = [(Mass beaker + liquid) – (Mass empty beaker)] (g)

Density = Mass/ Volume (g/mL)

Trial 1: Density = 7.9662 g/10.01 mL

= 0.7958 g/mL

Trial 2: Density = 15.8713 g/20.01 mL

= 0.7932 g/mL

Trial 3: Density = 23.7384 g/30.02 mL

= 0.7861 g/mL

Average value of Density = (0.7958 g/mL + 0.7932 g/mL + 0.7861 g/mL)/3

= 0.7917 g/mL

Observations:

The unknown liquid may evaporates if it remains open so it may cause some uncertainty.

The unknown liquid have colorless and some identical odor characteristics.

Few drops of unknown liquid were remained in volumetric pipette, which may cause

uncertainty in volume of unknown liquid.

Volumetric pipette work accurate at normal room temperature (25? C) but there was less

temperature in room.

3. Burette

Initial volume of unknown liquid = 10.01 mL

Second volume of unknown liquid = 20.01 mL

Final volume of unknown liquid = 30.02 mL

Mass liquid (g) = [(Mass beaker + liquid) – (Mass empty beaker)] (g)

Density = Mass/ Volume (g/mL)

Trial 1: Density = 7.9149 g/10.00 mL

= 0.79 g/mL

Trail 2: Density = 15.8126 g/20.01 mL

= 0.7902 g/mL

Trail 3: Density = 23.7427 g/30.00 mL

= 0.79 g/mL

Trial 1 Trial 2 Trial 3

Initial burette reading

(mL)

10.01 20.01 30.02

Final burette reading

(mL)

20.01 30.02 40.02

Volume of liquid

added (mL)

10.00 10.01 10.00

Total volume of

liquid in beaker (mL)

10.00 20.01 30.00

Mass empty beaker

(g)

69.4446 N/A N/A

Mass beaker + liquid

(g)

77.3595 85.2572 93.1873

Mass liquid (g) 7.9149 15.8126 23.7427

Density of liquid

(g/mL)

0.79 0.7902 0.79

Average value of Density = (0.79 g/mL + 0.7902 g/mL + 0.79 g/mL)/3

= 0.7901 g/mL

Observations:

The unknown liquid may evaporates if it remains open so it may cause some uncertainty.

The unknown liquid have colorless and some identical odor characteristics.

There was air bubble in the burette pipe, which may cause the uncertainty in measuring the

value of volume of unknown liquid.

Overall Average Value of Density = (0.802 g/mL + 0.7917 g/mL + 0.7901 g/mL)/3

= 0.7946 g/mL

In the second part of experiment, the unknown liquid is determine by checking it’s boiling point by

performing three trial.

Trial 1 Trial 2 Trial 3

Boiling point ( ?C) 81 78 77

Average value = (81 ? C + 78 ? C + 77 ? C)/3

= 79 ? C

Observations:

1. Water inside the beaker starts bubbling after 70 ? C.

2. Some pieces of boiling chip starts bubbling at 50 ?C, and then floating over the surface of hot

water.

3. Capillary tube starts bubbling rapidly at 80.5 ? C.

4. The filling up of capillary tube starts when bubbling stops and it happens slowly and gradually.

5. When vapor pressure becomes equal to the atmospheric pressure of room, that is 100.5 KPa

then capillary tube starts filling up the unknown liquid.

6. The cotton used to cover the mouth of 75 mm test tube was getting wet because of the vapors of

unknown liquid.

7. After disposing the remaining unknown liquid the capillary tube remain stuck inside the test

tube.

Graph:

Discussions: The probable identity of unknown Z6K was determined to be ethanol from its

Experimental density of 0.7946 g/mL. This compares to the literature value of 0.789

g/mL (Laboratory Manual, Krystyna koczanski and James Xidos). The experimental

density differs very less from the literature value. It’s experimental value of boiling point

is 79 ? C which is almost same as literature value of ethanol (78.5 ? C) and confirms the

unknown Z6K to be ethanol (Laboratory Manual, Krystyna koczanski and James Xidos).

Ethanol is colorless, slightly viscous than water and has identical odor. Observations of

unknown Z6K are consistent with the physical properties of ethanol.

The precision of the determined density was limited by the ability of the experimenter to

correctly fill the Graduated cylinder, volumetric pipette, burette, and measuring the mass

over the balance. The accuracy of glassware and balance is to 0.5 mL, 0.01 mL, 0.04 mL

and 0.0004 g respectively.

Sources of experimental error include:

Densities of liquid vary slightly with temperature. If the temperature in the lab was not 25°C,

the true values of the density of the unknown liquid may have differed from the literature

values for 25°C.

Few drops remain in burette while filling up the beaker.

Thermometer can touch the bottom of the beaker which can cause the error in reading.

Few drops could remain in volumetric pipette which causes error in Density.

The balance could give wrong reading as because of the disturbance due to other students over

the shelf on which the balance is placed on.

This lab could be improved by improving the method of drying the Graduated cylinder and beaker

before filling it with the unknown liquid. The glassware could be dried by small amount of acetone

could be used to rinse the flasks after washing. Any acetone remaining in the flask could be removed

by evaporation. Finally, the experimenter should remove droplets clinging to the neck or outside of the

flask by using a Kim Wipe.

Conclusion:

After careful consideration of all the test results and all the possible identities of the unknown, the

experimenters determined the unknown was, in fact, ethanol with density of 0.7946 g/mL and boiling

point of 79 ? C.

References:

Lab manual:

Koczanski, Krystyna; Xidos, James D. CHEM 1300 Laboratory Manual; UMSU Copy

Centre: Winnipeg, MB, Canada, 2013, pp 16.

Book with authors:

Olmested, John III; Williams, Gerg; Burk, Robert C. Chemsitry, Ist Canadian ed.; John

Wiley and Sons Ltd: Mississauga, Canada, 2010, pp 399 – 406.