Determination of Naphthalene's Molecular Weight
Using Boiling Point Elevation and Colligative Properties Analysis
Group 1. 강예지, 권수경, 김현중, 위정홍, 최지유
1. Abstraction
In this experiment, we measured the molecular weight of naphthalene using boiling point
elevation based on Raoult’s Law. A Beckmann thermometer and a mercury thermometer were used,
and the difference in results between the two types of thermometers was compared using a t-test.
Additionally, a t-test was conducted to check if the experimental results were statistically consistent
with the actual literature values. The results showed that the Beckmann thermometer, with more
significant figures, provided more precise values, and no statistically significant difference was
observed between the two thermometers. Consistency with literature values was also confirmed
statistically. Furthermore, we explored whether colligative properties apply not only to ideal
solutions but also to real solutions. We also investigated and designed methods for more precise
molecular weight measurements.
Keywords: Raoult's Law, Boiling Point Elevation, Molecular Weight Determination, Beckmann
Thermometer, Mercury Thermometer, Colligative Properties
2. Introduction
Molecular weight is one of the first parameters to understand when analyzing the properties of a
substance of interest. Many methods have been proposed for measuring molecular weight over time,
and these methods have gradually evolved to currently include techniques such as mass
spectrometry and gas chromatography (GC). However, these analytical methods require expensive,
high-quality equipment, making it difficult to use them at the undergraduate level. Therefore,
methods for measuring molecular weight using colligative properties, such as boiling point
elevation and freezing point depression, are employed.
1 / 17
In this regard, we focused on boiling point elevation and observed the differences in molecular
weight after measurements using a mercury thermometer and a Beckmann thermometer. From a
thermodynamic perspective, when the vapor pressure of the solvent decreases, the energy required
to vaporize from the liquid state to the gas state increases, resulting in a higher boiling point. The
Beckmann thermometer can measure temperatures with a precision of two decimal places, making it
easier to obtain accurate temperature readings, and thus we can expect more accurate experimental
values compared to the mercury thermometer. Additionally, we considered how much naphthalene,
the solute, should be dissolved in acetone, the solvent, in order for the experimental values to
approach the theoretical values. This experiment helped us understand the differences in results
when using the Beckmann thermometer and the mercury thermometer for measuring molecular
weight through boiling point elevation, as well as the phenomenon itself.
3. Procedure

Sample
substance
feature
Ketones, colorless liquids, volatile and flammable substances
Acetone (𝐶𝐻3 𝐶𝑂𝐶𝐻3 )
boiling point 56.08℃ molecular weight 58.08g/mol
density 0.791𝑔/𝑐𝑚3 (1)
White crystalline, aromatic hydrocarbons, sublimable
Naphthalene (𝐶10 𝐻8 )
melting point 80.3℃ molecular weight 128.17g/mol
density 1.16 𝑔/𝑐𝑚3 (2)
(A)
(B)
Figure1. (A) Acetone, (B) Naphthalene molecular structure

Experimental Apparatus
Cottrell boiling point measurement apparatus, Beckmann thermometer, clamps, two rubber
tubes, 50 mL graduated cylinder, pipette, pipette filler, condenser, 500 mL beaker, 1000 mL beaker,
hot plate.
2 / 17

Experiment 1
In this experiment, the boiling point measurement apparatus was set up by installing rubber tubes
on a fixed Cottrell boiling point apparatus to allow water to flow. The mercury bulb of the Beckmann
thermometer was also adjusted to align precisely with the position where acetone vapor is released
(Figure 2). Then, 25 mL of weighed acetone was placed in the apparatus and gradually heated in a
water bath. Measurements were taken by reading the scale of the zero-adjusted Beckmann
thermometer at 30-second intervals until there was no change in temperature. The same experiment
was conducted by adding 1 g of naphthalene three times to the acetone, for a total of 3 g, to measure
the boiling point.

Experiment 2
The procedure was carried out in the same manner as in Experiment 1, with the only change being
the replacement of the Beckmann thermometer with a mercury thermometer to repeat the
measurements.

Results Analysis
To analyze the boiling point as a function of naphthalene mass, a calibration curve was created, and
the equation of the line along with the R² value was determined. Subsequently, an F-test was
conducted to verify whether the standard deviation of the results from the differently conducted
experiments fell within the experimental error range. Based on the findings, a t-test was performed to
compare the results. Additionally, a t-test was carried out to assess whether the boiling point elevation
constant values of naphthalene mass/acetone, as presented in the literature, were statistically
consistent with the results of the two experiments.
(A)
(B)
Figure 2. (A) Boiling point measurement apparatus for Experiment 1 (3)
(B) Boiling point measurement apparatus for Experiment 2
3 / 17
4. Result
Table 1. Boiling points of acetone measured using the mercury thermometer and the Beckmann
thermometer.
(A) Beckmann thermometer
19.8
Acetone (g)
Naphthalene (g)
0.000
1.000
2.048
3.079
Boiling point (℃)
57.19
57.63
57.87
58.66
(B) Mercury thermometer
19.026
Acetone (g)
Naphthalene (g)
0.000
1.000
2.005
3.005
Boiling point (℃)
55.5
56.2
56.3
56.4
(A) represents the boiling point of acetone measured using the Beckmann thermometer, while (B)
represents the boiling point of acetone measured using the mercury thermometer. In the data obtained
from "Physical Chemistry Experiment Design, Group 1"(4) , only the volume of acetone is known to
be 25.0 mL, so by multiplying the density of 0.791 g/cm³, the mass of 19.8 g was calculated.
From the experimental results, it can be observed that the Beckmann thermometer, which has four
significant figures, allowed for more precise measurements compared to the mercury thermometer,
which has three significant figures. Additionally, it is evident from both experiments that the mass of
naphthalene is proportional to the boiling point according to Equation [1].
∆𝑇𝑏 = 𝐾𝑏 ×
1000×𝑤
𝑀×𝑊
[1](9)
𝐾𝑏 : Boiling point constant of acetone (℃ ∙ 𝑘𝑔/𝑚𝑜𝑙) w: Mass of naphthalene (g)
M: Molecular weight of naphthalene (g)
W: Mass of acetone (g)
4 / 17
Boiling point acetone
59,2
Beckmann thermometer
58,8
Mercury thermometer
Boiling point (℃)
58,4
58
y = 0,4521x + 57,145
R² = 0,9486
57,6
57,2
56,8
56,4
56
y = 0,2794x + 55,68
R² = 0,7837
55,6
55,2
0,000
0,500
1,000
1,500
2,000
2,500
3,000
3,500
Naphthalene (g)
Figure 3. This graph shows the boiling points of acetone measured using the Beckmann
thermometer and the mercury thermometer. Analyzing the experimental results, a correlation
coefficient of 0.995 or above typically indicates that the data fits well to a line. However, in this
experiment, the correlation coefficient for the Beckmann thermometer was 0.9486, and for the
mercury thermometer, it was 0.7837. This indicates a lower linearity than expected, suggesting that
experimental errors occurred. Additionally, the differing correlation coefficients for the two
thermometers in the same experiment confirm that the type of thermometer used affected the
experimental results.
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5. Discussion
(1) Setting the Experimental Conditions
The purpose of this experiment is to determine the molecular weight using boiling point
elevation. Boiling point elevation is a thermodynamic phenomenon where the boiling point of a
liquid increases when a non-volatile solute is dissolved in a solvent, compared to its pure liquid
state, and it falls under the category of colligative properties. Colligative properties refer to physical
characteristics that depend on the relative number of solute particles, regardless of the type of
solute, and they are applicable in ideal solutions. Therefore, while some real solutions may deviate
significantly from Raoult's Law, dilute solutions can still satisfy Raoult's Law.(5) The threshold for
a dilute solution may vary depending on the solute and solvent, but it generally refers to solutions of
0.2 M or lower. For this reason, naphthalene was added three times, in increments of 1 g each, to 25
mL of acetone. Additionally, since acetone is a flammable substance, the experiment was conducted
using a water bath.
Furthermore, the formula used to measure the molecular weight assumes that there are no
changes in pressure. To ensure this, a Cottrell boiling point apparatus was employed. This apparatus
does not prevent acetone vapor from escaping, thus maintaining the internal pressure equal to
atmospheric pressure, and the circulating cold water causes the evaporated acetone to liquefy.
Therefore, using this apparatus allows for the maintenance of constant pressure and prevents
changes in volume, thereby increasing the precision of the experiment.
(2) Comparison of Vapor Pressure Lowering and Boiling Point Elevation
Vapor pressure lowering refers to the phenomenon where the vapor pressure of a solvent
decreases when another substance (solute) is dissolved in it. Boiling point elevation, on the other
hand, is the phenomenon where the boiling point is raised when a non-volatile solute is present in
the solvent compared to pure solvent. According to Raoult's Law, the vapor pressure of a solution
decreases in proportion to the mole fraction of the solute in the solution, which affects the entropy
of the solution.
6 / 17
Pure solvent molecules have a disordered state and possess corresponding entropy. The
magnitude of vapor pressure indicates a tendency for the system to reach a higher entropy state, that
is, the gaseous state. However, when a solute is dissolved in the solvent, the entropy of the solution
increases, resulting in a smaller entropy gain during vaporization compared to the pure solvent.
Consequently, vaporization of the solution occurs less spontaneously than that of the pure solvent,
leading to a lower vapor pressure of the solvent in the solution compared to that of the pure
solvent.(6)
The boiling point is defined as the temperature at which the vapor pressure of a liquid equals the
external pressure. When solute particles lower the vapor pressure, a higher temperature is required
to equal the atmospheric pressure. In other words, the boiling point increases, which indicates that
vapor pressure lowering is synonymous with boiling point elevation.
(3) Considerations on the Conditions for Colligative Properties
Colligative properties depend on the relative number of solute particles and are independent of
the chemical species involved. These properties include vapor pressure lowering, boiling point
elevation, freezing point depression, and osmotic pressure, which arise because the presence of
solute decreases the chemical potential of the solvent. Colligative properties are valid only in ideal
solutions, while in real solutions, they can be influenced by the type of solute.
The first reason for this is the difference in interactions between solute and solvent. In ideal
solutions, it is assumed that the interactions among solvent-solvent, solute-solute, and solute-solvent
are the same. However, in real solutions, specific solutes may interact more strongly or weakly with
the solvent. If the intermolecular forces between solvent-solvent and solute-solute are stronger than
those between solute and solvent, the actual vapor pressure will be greater than that predicted by
Raoult's Law. Conversely, if the solute-solvent interactions are stronger, the actual vapor pressure
will be lower than the value calculated by Raoult's Law.
The second reason involves ionization or chemical reactions. If the solute ionizes or reacts in the
solvent, colligative properties do not simply correlate with the number of solute particles. For
example, when NaCl dissolves in water, it dissociates into Na⁺ and Cl⁻ ions, increasing the particle
count compared to the original amount. Since boiling point elevation is proportional to the total
particle concentration, the van 't Hoff factor (i), which accounts for the number of particles after
ionization, must be considered in calculations.(7) However, the actual boiling point elevation is
often measured to be lower than the theoretical value because ions in solution can temporarily
7 / 17
associate with oppositely charged ions to form ion pairs.(8) These ion pairs behave as a single
particle, resulting in the observed boiling point elevation being greater than that calculated with i=1
(assuming no ionization) and less than that calculated with i=2 (assuming complete ionization).
(4) Analysis of the Boiling Point Elevation Formula
When a solute is added to a pure solvent, the chemical potential of the solvent decreases. As the
chemical potential of the solvent decreases, the temperature at which the solvent in the gas phase
and the solvent in the liquid phase have the same chemical potential (the boiling point) reaches
equilibrium at a pressure of 1 atm. The chemical potential at equilibrium can be expressed with
equation [2].
𝛍𝑨 = 𝝁̇ 𝑨 + 𝑹𝑻 𝐥𝐧 𝒙𝑨 [2](𝟗)
According to this equation, when the chemical potential of the solvent decreases, the normal boiling
point increases, and this increase is proportional to the mole fraction of the solute in dilute solutions.
By using this principle to derive the boiling point elevation formula, we get ∆𝑇𝑏 = 𝐾𝑏 × 𝑥𝐵 (9) .
However, in experiments, molality is used instead of the mole fraction of the solute. This is because,
when x_B << 1, the mole fraction and molality are proportional to each other.
Therefore, the equation we actually use is ∆𝑇𝑏 = 𝐾𝑏 × m,(9) which shows that when a solute is
added to a pure liquid solvent, the boiling point of the solvent rises, and this elevation in boiling point
increases as more solute is added, proportional to the molality of the solution.
(5) Comparison of Results Based on Types of Thermometers and Discussion of
Experimental Results
The Beckmann thermometer is a specialized mercury thermometer capable of measuring a wide
range from -20°C to 180°C, with a precision selectable to 1/100°C, typically measuring about 40 to 50
cm in length. Its temperature scale is divided into increments of about 5°C and consists of 1000 divisions,
allowing for precise measurement of small temperature changes. It is convenient for measuring minute
temperature variations by breaking the mercury column or setting a reference temperature with the Ushaped upper part of the tube.
In contrast, a standard mercury thermometer can measure in the range of 0°C to 100°C and can also
measure temperatures above 100°C, but with greater error. Generally, it is divided into 100 increments
8 / 17
for the 0°C to 100°C range, allowing measurements in 1°C increments, which is less precise than the
Beckmann thermometer.
In boiling point elevation experiments, the changes in boiling point are very small, so a Beckmann
thermometer is typically used for precise measurements. The Beckmann thermometer can measure with
up to four significant figures, making it advantageous for experiments. However, in this particular
experiment, difficulties arose in using the Beckmann thermometer, and only a standard mercury
thermometer was used. Instead, the measurements from the Beckmann thermometer used in the physical
chemistry experiment design of the first group were referenced, and a t-test was conducted to compare
the results.
Table 2. t-test Results for Beckmann Thermometer and Mercury Thermometer Measurements
(A)
𝐹𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛
21.65
𝐹𝑡𝑎𝑏𝑙𝑒 (𝑑𝑓1=𝑑𝑓2 =2)
39.00
(B)
𝑇𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛
1.453
𝑆𝑝𝑜𝑜𝑙𝑒𝑑
552.2
𝑇𝑡𝑎𝑏𝑙𝑒
2.776
df
4
To determine whether the standard deviations of the two experimental values are statistically different,
an F-test was conducted. Since each value was measured three times, the degrees of freedom are 2.
According to equation [3], 𝐹𝑡𝑎𝑏𝑙𝑒 = 39.00 and 𝐹𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 21.65. Since 𝐹𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛 < 𝐹𝑡𝑎𝑏𝑙𝑒 , there
is a greater than 5% probability that the two results come from populations with the same standard
deviation. Therefore, the difference is not significant.
𝑆2
𝐹𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 12 (𝑆1 > 𝑆2 ) [3](10)
𝑆2
Next, based on the results of the F-test, since the difference in standard deviations is not significant,
a t-test was conducted using equation [4].
𝑡=
|𝑥
̅̅̅1̅+ ̅̅
𝑥̅2̅|
𝑠𝑝𝑜𝑜𝑙𝑒𝑑
𝑛1 𝑛2
√𝑛 +𝑛
1
2
𝑠 2 (𝑛1 −1)+𝑠22 (𝑛2 −1)
, 𝑆𝑝𝑜𝑜𝑙𝑒𝑑 = √ 1
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𝑛1 +𝑛2 −2
[4](10)
At a 95% confidence level, with degrees of freedom (𝑛1 + 𝑛2 − 2) = 4, the calculated value is
𝑇𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛 =1.453 and the critical value is 𝑇𝑡𝑎𝑏𝑙𝑒 =2.776. Therefore, since 𝑇𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛 < 𝑇𝑡𝑎𝑏𝑙𝑒 , we
can conclude that the difference between the two means is not statistically significant.
In the next experiment, if we take photos while reading the scale of the mercury thermometer to
carefully verify the readings, I believe the discrepancies between the two experimental results will be
reduced. This approach will help minimize subjective errors in reading the scale and yield more accurate
data.
Additionally, the experimental results were influenced by various sources of experimental error
beyond just significant figures. During the water bath process with acetone, the bath temperature was
adjusted mid-experiment, leading to inadequate control of variables. Due to inexperience with the
equipment, we were unable to start the experiment immediately after adding naphthalene. Furthermore,
as the temperature of the apparatus increased, the parafilm connecting the thermometer to the Cottrell
boiling point measurement device melted, resulting in an inability to maintain a constant pressure.
10 / 17
(6) Comparison of Literature Values and Experimental Values Using t-test
Table 3. Comparison of Literature Values and Experimental Values of M/𝐾𝑏 Using t-test
(A) Beckmann Thermometer
ΔTb
0.44
0.24
0.79
M/𝐾𝑏
114.8
431.0
196.8
Average
247.5
standard dev.
164.1
95% confidence
407.6
T for 95%
4.303
ΔTb
0.7
0.1
0.1
M/𝐾𝑏
75.1
1054
1579
Average
903
standard dev.
763
95% confidence
1897
T for 95%
4.303
(B) Mercury Thermometer
(C) Literature Values
M (g/mol)
128.18
𝐾𝑏 (℃ ∙ 𝑘𝑔/𝑚𝑜𝑙)
1.71
M/𝐾𝑏
75.0
The objective of this experiment is to measure the molecular weight of naphthalene; however,
the unknowns in this experiment include not only the molecular weight (M) but also the boiling
(11)
point elevation constant (𝐾𝑏
). Therefore, the results of this experiment focused on deriving the
M/K_b value.
Using equation [5] to conduct a t-test, it was found that the M/𝐾𝑏 values from both experiments
fell within the 95% confidence interval of the literature values. Therefore, it can be concluded that
the experimental results are consistent with the literature values within the margin of error.
95% 𝑐𝑜𝑛𝑓𝑖𝑑𝑒𝑛𝑐𝑒 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 = 𝑥̅ ±
11 / 17
𝑡𝑠
√𝑛
[5](10)
(7) Introduction to Molecular Weight Measurement Methods

What is Mass Spectrometry
This method measures the mass of a substance as a mass-to-charge ratio (m/z), and the ionization
process is essential before the sample enters the mass spectrometer.

Principle
The most important factor in the ionization process is the condition for transferring internal energy.
Some methods cause significant fragmentation with high energy, while others generate molecular
ions in a gentle manner. There are various types of ionization processes depending on the target
application. The different types of ionization methods and their main applications are summarized in
Table 4.
Table 4. Different ionization methods (12)
Ionization
method
EI
Separation
Ion type
Sample type
𝑀∙+, fragments
Nonpolar and some polar organic compounds
GC
Nonpolar and some polar organic compounds
GC
technique
[M + H]+ ,
CI
FAB
Thermospray
[M + H]− , 𝑀∙+
[M + H]+ , [M + H]−
Peptides, proteins, lipids, carbohydrates,
Oligosa, ccharide, nucleotides, oligonucleotides
[M + H]+ , [M + H]− , [M
Polar compounds
LC
Polar compounds, drugs
LC
+ 𝑁𝐻4 ]+
APCI
[M + H]+ , [M + H]−
ESI
[M + nH]𝑛+ , [M + nH]𝑛−
LC, CE
Peptides, proteins, lipids, carbohydrates, oligosa
ccharide, nucleotides, oligonucleotides,
LC, CE
Low mass polymer
MAI, DI
[M + H]+ , [M + H]−
Peptides, proteins, lipids, carbohydrates, oligosa
ccharide, nucleotides, oligonucleotides, polymers
LC, CE
After ions are generated, they must be separated based on their mass. For this reason, there are
various types of mass spectrometers. The three important characteristics of mass spectrometers are
the mass analysis upper limit, transmission efficiency, and resolution. The mass analysis upper limit
refers to the highest value of the m/z ratio that can be determined. Transmission efficiency indicates
the ratio of ions reaching the detector from the ion source, while resolution refers to the ability to
distinguish two ions as different signals even with small differences in molecular weight.
12 / 17

Types of 𝐀𝐧𝐚𝐥𝐲𝐳𝐞𝐫𝐬 (𝟏𝟑)
Quadrupole Analyzers: Also known as quadrupole analyzers, these are the most commonly used
types of analyzers. They consist of four rods arranged in a quadrupole shape. When positive ions
enter the quadrupole's internal space, they are attracted toward the negative pole. When the poles
switch, the direction of the ions changes. Below is a brief introduction to the types of mass
analyzers.
Quadrupole Ion Trap: This traps only the desired ions within a range of the same frequency
quadrupole while expelling the others. This selectivity is an advantage, and the separated ions
undergo fragmentation due to collision gas. Additionally, its ability to capture and accumulate
smaller ions is also regarded as an advantage.
Double-Focusing Magnetic Sector: This analyzer uses magnets to generate an electric field,
causing ions to accelerate. The ions undergo circular motion, with the diameter determined by their
velocity, magnetic field strength, and m/z value. The kinetic energy of the ions arriving at the
detector is made uniform within the device, enhancing resolution.
Time-of-Flight Mass Spectrometer: This is the simplest mass spectrometer and is used in
conjunction with other chromatography techniques. The principle is that ions receive the same
energy in the acceleration region and are accelerated to the detector, with lighter ions detected first,
followed by heavier ions.
Fourier Transform Ion Cyclotron Resonance: The basic principle is that ions move at lower
speeds in the ion orbit; the stronger the magnetic field, the smaller the diameter of the orbit. While
the ions are circulating within the magnetic field, they generate an observable and detectable
current. This current is transformed into a specific frequency for detection. It shows high resolution
and accuracy, highlighting its advantages in the analysis of biological substances.
13 / 17
𝐃𝐞𝐭𝐞𝐜𝐭𝐨𝐫𝐬(𝟏𝟒)
: Ions arriving at the detector generate signals, and their kinetic energy is used to release the next
electron. Below is a brief description of the types of detectors.
Electron Multiplier: Amplifies the signal through the interaction between electrons and dynodes.
Faraday Cup: Induces a current from the instantaneous release of electrons, with high tolerance.
Photon Multipliers: Operates in two modes; in the positive ion mode, the amplified ions are
accelerated toward the negatively charged dynode, while in the negative ion mode, the ions are
accelerated toward the positively charged dynode. This is followed by conversion to photons via a
phosphorescent screen and detection by the photomultiplier.
What is Victor Meyer Method
The Victor Meyer method is a technique for determining the molecular weight of a substance by
measuring the density of the vapor when a relatively volatile liquid is converted into gas. While this
method may not be suitable for measuring the molecular weight of naphthalene, it is included in the
discussion to introduce this molecular weight measurement technique.
Principle
In this method, air with a volume equal to that of the known mass of the substance is evaporated
from an evaporation tube. This evaporated air is then collected above water or mercury, and its
volume is measured under known atmospheric pressure and temperature conditions. The key to this
experiment is that the vapor state of the reagent changes the height of the liquid column, and this
volume is used along with the ideal gas law to calculate the molecular weight.
It is important to note that when calculating the pressure applied to the reagent, one must consider
the atmospheric pressure minus the vapor pressure.(15) Additionally, since the reagent is not
directly evaporated but rather heated in a water bath, only reagents with a boiling point below
100°C can be used. If this condition is not met, the reagent may re-liquefy, leading to inaccurate
measurements.
14 / 17
Calculation Formula
When the temperature is t°C, let the saturation vapor pressure of water be p' mmHg, and the partial
pressure of dry air be (P - P') mmHg. If the volume of this air is converted to conditions of 0°C and
1 atm, it can be expressed as:
𝑉0 =
273.15 × (𝑝 − 𝑝′)
× 𝑉 (14)
(273.15 + 𝑡) × 760
Here, 𝑉0 represents the volume of the sample when it is in the gas state at 0°C and 1 atm. If the
mass of the sample collected before the experiment is W g, then the hypothetical air density of this
substance at 0°C and 1 atm is W/𝑉0 g/cm³. From the calculations, it can be determined that the
molecular weight of the substance is given by:
Molecular Weight=22.414×𝑊/𝑉0
15 / 17
6. Conclusion
In this experiment, the molecular weight of naphthalene and the boiling point elevation constant
of acetone were measured using boiling point elevation. Since boiling point elevation is based on
Raoult's Law, the experiment was conducted with dilute solutions and under constant pressure
conditions. Two types of thermometers, the Beckmann thermometer and the mercury thermometer,
were used, with the Beckmann thermometer providing more precise results due to its greater
number of significant figures. The t-test results indicated that there was no statistically significant
difference in the means of the experimental values, and when compared to the actual literature
values, the two values were found to be in agreement within the experimental error range.
Furthermore, the concept of colligative properties was explored. Colligative properties apply well
to ideal solutions where solvent-solvent, solute-solute, and solute-solvent interactions are the same,
but in real solutions, the differences in solute-solvent interactions can affect the number of solute
particles. In the case of electrolyte solutes, the actual number of particles increases due to
ionization, so the van 't Hoff factor (i) must be considered. An analysis of the boiling point elevation
equation revealed that the chemical potential of the solvent decreases due to the solute and is
proportional to the mole fraction of the solute. When the mole fraction is very small, molality can be
used to calculate boiling point elevation. However, because the change in boiling point elevation is
minimal, it is not widely used for molecular weight measurements.
To achieve more accurate measurements, the need for additional analytical methods was
investigated after exploring mass spectrometry and the Victor Meyer method. A future experiment
was designed to measure the molecular weight of naphthalene using gas chromatography (GC)
combined with mass spectrometry (MS).
In conclusion, this experiment provided an understanding of the principles and limitations of
measuring molecular weight through boiling point elevation, confirmed the agreement between
experimental results and literature values, and highlighted the necessity for additional analytical
methods for more accurate molecular weight determination.
16 / 17
7. References
(1)
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