CHEMISTRY - Laboratory Logbook Entry
LABORATORY EXERCISE: Density and Boiling Point Determination of
an Unknown liquid
Lab Instructions:
PAGE 1
Objectives:
1. To identify an unknown liquid using two physical properties: the density
and boiling point.
Discussion and Review:
In this experiment we will examine additional physical properties of a liquid. Two of the
more important physical properties of pure substances are their density and boiling point.
The boiling point of a liquid is the temperature at which that liquid is converted to a
gaseous state. Boiling point is formally defined as the temperature at which the vapor
pressure of the liquid becomes equal to the pressure at the surface of the liquid. The
boiling point of a liquid can change if the pressure at the liquid's surface changes. Since
pure substances have a distinct boiling point, boiling points are sometimes used to
determine the purity of substances.


Density is an intensive property that does not depend on the amount of the
substance that is used.
Boiling points are recorded in the Handbook of Chemistry and Physics, and can
be found in the sections titled "Physical Constants of Organic Compounds" and
"Physical Constants of Inorganic Compounds".
PAGE 2
PART 1
Purpose: Determining the Densities of an unknown liquid
DISCUSSION
Density is an important property of matter. By itself, or in conjunction with other
properties, density can be used to identify substances. Density is defined as the quantity
of matter in a given unit of volume. This relationship, expressed mathematically, is:
Density = mass (g) or D = m
Volume (mL)
V
You will be expected to use the measuring skills and techniques developed in earlier
lab sessions and in the first part of this experiment to find the mass and volume of
different substances. You will use these data to calculate the density of these
substances.
Materials Used:
Beaker
1-Disposable pipette
Electronic balance
10-mL graduated cylinder
Unknown liquid
PROCEDURES:
Part I. Densities of Liquids at Room Temperature.
1. Clean and dry your 10 mL graduated cylinder.
2. Weigh the cylinder carefully and record its mass to the nearest hundredth.
3. Go to the hood area, and pour out approximately 10 mL into a dry-cleaned beaker.
4. Go back to your lab station and pour some of the unknown in your graduated
cylinder. Record the volume on your data table. (Be sure to take your
measurement from the bottom of the meniscus.)
5. Weigh the cylinder and liquid on the balance. Record the mass.
6. Pour some more of the unknown liquid from your beaker to the volume that was
previously recorded in step 4. Record the new volume.
7. Weigh the cylinder and the new volume on the balance. Record the mass.
8. Using the disposable pipette, add some more of the unknown liquid to the previous
volume. Record the new volume.
9. Weigh the cylinder and the new volume. Record the mass.
10. Clean out the graduated cylinder and beaker with tap water and dry the beaker.
PAGE 3
PART II
Purpose: To determine the boiling point of one unknown liquid.
Materials Used:
Striker
1 Unknown liquid
1-2 small rubber bands
Thermometer
beaker
closed-end capillary tubes (melting point tubes)
10-12 mm diameter test tube
Laboratory Burner
Ring stand
Iron ring
Wire gauze
PROCEDURES:
Part II. Boiling Point
1. Make a test tube assembly by using the following directions and illustration.
a. Place about 1 mL of liquid 1 in a 10-12 mm diameter test tube.
b. Using a small rubber band, attach a thermometer to the outside of the test tube.
The thermometer bulb should be even with the test tube's bottom.
c. Insert an inverted closed end capillary tube into the test tube.
2. Make a water bath assembly by using the following directions and illustration.
a. Half fill a 100 mL or larger beaker with warm tap water. [Note: a water bath is
used if the boiling point of the material is expected to be less than the boiling point of
water; otherwise, an oil bath is needed.]
b. Place the above test tube assembly in the water bath so that the surface level
of the alcohol in the test tube is beneath the surface level of the water bath.
c. Place the beaker on the wire stand and, stirring frequently to insure even
heating, carefully heat the water bath with your heat source until the water bath boils and
a rapid stream of bubbles continuously emerges from the capillary tube.
d. Remove the heat source and begin observing the stream of bubbles.
e. When the last bubble emerges from the capillary tube, record the temperature.
3. Reheat the water bath and repeat the cooling process two more times. Record the
temperature reading after each trial, and average all three trials.
DATA ANALYSIS
Data Table #1: Unknown #1 Mass(g), volume (mL), and density (g/mL)
measurements
Mass of Empty
Cylinder (g)
Mass of Liquid &
Cylinder in Grams
(to nearest 0.01g)
Mass of Liquid in
Grams
(to nearest 0.01g)
Volume of Liquid in
mL
(to nearest 0.1mL)
Density of Liquid in
g/mL
(to nearest 0.1g/mL)
CALCULATIONS for Unknown #1
A) Mass of the Liquid (g) = [Mass (g) Liq + cylinder] - [Mass (g) empty cylinder]
B) Density (g/mL) = mass (g)/volume(mL)
C) Averaged Density (formula needed) = __∑x_ = sum of density (g/mL)
n
number of trials
TABLE # 1: Mass (g) and Volume (ml) for UNKNOWN #1
Trials
1
2
3
Mass (g)
Volume (mL)
GRAPH #1
1. Construct a Mass (y axis) vs Volume (x axis) graph for unknown #1 using the
measurements from the data table.
2. Calculate the slope (page R 76 in text for chemistry) of the line graphs.
(Show the formula used, and calculations on the graph for each line) Be sure
to clearly label the graphs for the unknown.
PART II
DATA TABLE #2: Boiling point of Unknown 1 (ºC)
Trials
BP (ºC) - Unknown 1
1
2
3
AVERAGES
Calculations: Average
Average for Unknown # 1: _∑x_ = sum of BP (ºC)
n
number of trials
LIST OF KNOWNS
n-butanol
2-propanol
Ethanol
Octane
Ethyl acetate
1-octyl alcohol
Density
0.809
0.786
0.789
0.703
0.773
0.8240
B.P.
117 ºC
82 ºC
78.4 ºC
126 ºC
78.9 ºC
194 ºC
DATA TABLE# 3: Lab data comparing the AVERAGED DENSITY (g/mL),
SLOPES (g/mL) (from graph), and BOILING POINTS with TRUE values for the
unknowns.
Unknown
ID
True
Density
(g/mL)
Slope
Density
(g/mL)
%
Error
slope
Density
Measured
Averaged
Density
(g/mL)
%Error
Average
Density
(g/mL
True
BP (ºC)
Measured
Average BP
(ºC)
% Error
BP (ºC)
ERROR CALCULATIONS below data table:
Calculate the percent error for your measurements. Be sure to provide the
formula used for percent error. Show all work. Calculate the % error for your
average Density, the slopes, and the BP.
% Error = |true density (g/mL) - measured density (g/mL)|_
True density (g/mL
x 100
% Error = |true BP (ºC) - measured BP (ºC) |_ x 100
True BP (ºC)
DATA TABLE #4: Comparison of the Calculated average density; slope; and true
value for each of the unknowns Percent Error (%)
Unknown # 1 % Error
Averaged Density
Slope
Boiling Point
Bar Graph #1: Comparison of the Percent Error for each of the unknowns (should
include your measured averages, slopes, and BP.
CLASS ANALYSIS:
Calculation for your group average
DATA TABLE #5: Data table of class group averages for Density (g/mL) and
Boiling Points (for Unknown)
Group Number
1.
2.
3
4
5
6
7
8
9
10
11
12
13
14
15
Class range
∑x
N (number of
groups)
X
(Average/mean)
Density
(g/mL)
Unknown
#1
B.P (ºC).
Unknown
#1
DATA TABLE #6: CLASS PERCENT ERROR for Density and B.P. for 1 unknown
liquid to the known values & Percent errors
UNKNOWN Property
Measured
#1
Measured
Value
Known Value
% Error
Density
(g/mL)
Boiling Point
(ºC)
CALCULATIONS: % Error for Class averages for Density (g/mL) and Boiling
Point (ºC) for Unknown #1
% Error = |true density (g/mL) - measured density (g/mL)|_ x 100
True density (g/mL
% Error = |true BP (ºC) - measured BP (ºC) |_ x 100
True BP (ºC)
BAR GRAPH #2: Bar Graph for Class % Error for Density and B.P. for Unknown
liquid (also include your % error)
CONCLUSIONS
A. Was purpose met
B. comments about percent error for density and boiling
point (personal error)
C. compare error for personal measurements and slope (for
density)
D. comment on class error
E. compare personal error to class error
F. discuss possible causes for the error (both personal and
class)
G. what needs to be done to decrease error (both personal
and class)
H. summary statement