EXPERIMENT
Physical Properties:
Identification of a Pure Liquid
7
Prepared by Edward L. Brown, Lee University and
Verrill M. Norwood, Cleveland State Community College
OBJECTIVE
To identify an unknown liquid by comparing the experimental and theoretical
boiling points and densities.
A
P P A R A T U S
balance
Bunsen burner
disposable glass pipette
ring stand
thermometer (-10ºC to 150ºC)
ring clamp
1 mm cross section of rubber hose
wire gauze
test tube (10 – 15 cm long)
striker (lighter)
boiling stone
Thermometer (or test tube) clamp
test tube clamp
1000 mL beaker
C
APPARATUS
AND
CHEMICALS
H E M I C A L S
Unknown liquid (~ 3.5 mL)
Physical properties are those characteristics of a substance that can be observed or
measured without chemically changing the substance. Taste, odor, and color are examples
of physical properties that are more observable than measurable. Measurable physical
properties include melting point, boiling point, refractive index, density, solubility, and
viscosity. Many scientists devoted their lives to collecting and tabulating the physical
properties of the elements and compounds. Two books have emerged as references in this
area: N. A. Lange’s Handbook of Chemistry and The Chemical Rubber Company’s
Handbook of Chemistry and Physics. The “handbook” for this lab has been condensed to
Table 1 – eight organic liquids and their densities, melting points and boiling points.
With meticulous laboratory care, your collected data and this table will allow you to
identify your particular unknown.
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Physical Properties: Identification of a Pure Liquid
The boiling point of a liquid is the temperature at which the vapor pressure of the liquid
equals the pressure of the atmosphere above the liquid. At the boiling point, bubbles of
vapor form within the liquid and rise unimpeded to the top of the liquid, breaking the
surface tension and releasing the vapor into the atmosphere above. If the pressure of the
atmosphere above the liquid is exactly 1 atmosphere, then the temperature at the boiling
point is called the normal boiling point. Because boiling points are pressure dependent,
certain corrections to the boiling point measurement must be made if the pressure is
significantly different from 1 atmosphere. Fortunately for this lab, as long as the
atmospheric pressure is 760 mmHg +/- 10 mm Hg, then the correction will be less than
0.3º C (well within the error range of reading a thermometer).
The density of a substance relates two common measurements, mass and volume, as a
ratio that is unique (thus meaningful) to the substance being studied. Whether one has
only a speck of a pure substance or a warehouse, the density will be the same.
D=
M
V
Equation 1
In this lab, mass will be determined using a balance. It is IMPERATIVE that you use the
SAME BALANCE when making measurements during the SAME LAB!! We are generally
interested in the differences in mass and this measurement is accurate only if the SAME
INSTRUMENT is used for both measurements.
Typically, liquid volumes are determined using calibrated glassware such as graduated
cylinders, volumetric flasks, burettes, and pipettes. In today’s lab, a “green chemistry”
approach to determining the density and boiling point will be employed. In this green
chemistry approach, the total volume of liquid unknown you will be given is ~ 3.5 mL.
After the density and boiling point of the liquid is determined, there will be ~ 1
mL of chemical waste that must be placed in the labeled waste container.
A.
Thermometer Calibration
PROCEDURE
Useful measurements result only from using equipment that is precise and accurate.
Calibration is a process where equipment inaccuracies are exposed and corrections are
determined. During any calibration process, it is critical that students exercise the
greatest amount of precision possible in order to obtain an accurate instrument. At
the front of the class are two large beakers of water – one containing ice and water and the
CHEM 1001 - Experiment 7
7-2
Physical Properties: Identification of a Pure Liquid
other containing boiling water. You and your lab partner will measure the temperature of
water in the two beakers to calibrate your thermometer.
1. Place your thermometer in the beaker containing ice and water. Make sure the
beaker has plenty of ice (at least ½ ice) and carefully stir the contents with your
thermometer to make sure the entire solution is at the same temperature.
2. After 1 minute, record the temperature (make sure the thermometer is still in
the ice water when you read the temperature – don’t lift it out) to the nearest
0.2 °C [Data Sheet].
3. Next, place the same thermometer in the beaker containing the boiling water.
Make certain the water is boiling and do not allow the thermometer to touch the
sides of the beaker.
4. After 1 minute record the temperature to the nearest 0.2 °C [Data Sheet] - make
sure the thermometer is still in the boiling water when you read the
temperature.
B.
Density of a Liquid Unknown
5. Obtain a numbered vial containing a liquid unknown – Do Not Share This
Unknown With Anyone Except Your Lab Partner!
6. Record the four digit number of your unknown liquid [Data Sheet].
7. Obtain a micropycnometer and a glass pipette from the Instructor’s Desk.
8. Place a small beaker on the balance and TARE its mass to 0.000 g. Then, place
the micropycnometer into the beaker and record its mass [Data Sheet].
9. Place a rubber pipette bulb on the pipette. Use this pipette to transfer your
unknown liquid into the micropycnometer.

Avoid air bubbles

Make sure the micropycnometer is completely filled with liquid

Don’t break the glass tip of your pipette inside the micropycnometer
10. Place a small beaker on the balance and TARE its mass to 0.000 g. Place the
micropycnometer filled with unknown liquid in this beaker and record its mass
[Data Sheet].
11. Remove the unknown liquid with the same delivery pipette – Place This Liquid
In A Clean, Dry Test Tube (this will be used in Step 15)!!
CHEM 1001 - Experiment 7
7-3
Physical Properties: Identification of a Pure Liquid
12. Return the vial containing any “extra” unknown liquid to the Instructor’s
Desk.
13. Fill the micropycnometer to the top with distilled water using the pipette you
constructed.

Avoid air bubbles

Make sure the micropycnometer is completely filled with water

Don’t break the glass tip of your pipette inside the micropycnometer
14. Place a small beaker on the balance first and TARE its mass to 0.000 g. Place the
micropycnometer filled with water in this beaker and record its mass [Data
Sheet].
C.
Boiling Point of a Liquid Unknown
15. Add a boiling stone to the Unknown liquid already in the Pyrex test tube from
Step 11 [see Figure 2].
16. Secure the test tube with a three-fingered clamp
and lower it into a beaker filled with tap water.
17. Heat the water rapidly with a Bunsen burner until
the unknown liquid begins to boil.
18. Clamp (or hold) your thermometer approximately
1 cm above the boiling unknown liquid for about
20 seconds before recording the temperature to
the nearest 0.2 °C [Data Sheet] – the liquid
should be dripping off the end of your
thermometer when you read the temperature.
Lift the test tube out of the hot water as soon as
possible (without burning yourself) after
recording the boiling point to prevent the
vaporization of your unknown into the lab’s
atmosphere.
D.
Boiling Stones
Figure 2
Unknown Identification
19. Compare your unknown’s density and boiling point to those recorded in Table 1 to
identify your unknown. You will report the identity of your unknown in the
online report sheet for this lab.
CHEM 1001 - Experiment 7
7-4
Physical Properties: Identification of a Pure Liquid
Substance
Chemical
Formula
Density
Melting
Boiling
(g/mL)
Point (°C)
Point (°C)
Acetone (1)
C3H6O
0.79
-95.4
56.2
2,3-Butanedione (2)
C4H6O2
0.98
-2.4
88
Cyclohexanol (3)
C6H12O
0.96
24.0
161
Chloroform (4)
CHCl3
1.48
-63.5
61.7
Bromoform (5)
CHBr3
2.90
7.5
150
Hexane (6)
C6H14
0.66
-94.0
69
Isopropyl alcohol (7)
C3H8O
0.79
-89.5
82.4
Methyl alcohol (8)
CH4O
0.79
-98.0
64.7
Table 1
Waste Disposal:
Place any liquid remaining from the boiling point determination in
the waste beaker in the hood. You should have returned the unknown vial (along with
any unused liquid unknown) to the Instructor’s desk in Step 12.
Lab Report:
Once you have turned in your Instructor Data Sheet, lab attendance will
be entered and you will be permitted to access the online data / calculation submission part
of the lab report (click on Lab 7 – Identification of an Unknown Liquid). Enter your
data accurately to avoid penalty.
CHEM 1001 - Experiment 7
7-5
CHEM 1001 - Lab 7
Student Data Sheet
Actual Freezing Point of Water
0
ºC
Actual Boiling Point of Water
100
ºC
Freezing Point of Water recorded on Your Thermometer
ºC
Boiling Point of Water recorded on Your Thermometer
ºC
Unknown Number (liquid)
Mass of micropycnometer
g
Mass of micropycnometer + unknown liquid
g
Mass of micropycnometer + water
g
Boiling Point of the unknown liquid
ºC

Name:
CHEM 1001 - Lab 7
Instructor Data Sheet
Actual Freezing Point of Water
0
ºC
Actual Boiling Point of Water
100
ºC
Freezing Point of Water recorded on Your Thermometer
ºC
Boiling Point of Water recorded on Your Thermometer
ºC
Unknown Number (liquid)
Mass of micropycnometer
g
Mass of micropycnometer + unknown liquid
g
Mass of micropycnometer + water
g
Boiling Point of the unknown liquid
ºC
CHEM 1001 - Experiment 7
7-6