Melting point diagram of the durene-naphthalene system
A binary phase diagram of durene/naphtalene was compiled and the corresponding ideal
phase diagram was calculated. The melting enthalpies of durene and naphthalene were
determined to (20.4  0.4) kJmol-1 and (18.9  1.8) kJmol-1.
Linus Becker
Katrin Niedermann
Zürich,29.4.05
Assistent: Dr. Pavel Bushev
1
1 Introduction
A phase diagram for durene-naphtahalene was created by measuering its freezing points. In the
experiment, a freezing curve for to binary mixture with known composition was measured. By a
quantitative analysis of the data, the meltingenthalpies of the two materials could be determined.
2 Procedure
Gadget:
• Sample tube consisting of glas containing a stirring wire and a thermocouple.
• Reference thermocouple
• x,t- chart recorder
Fig. 1: Sample tube
Calibration:
The reference and the sample thermocouple were hold in ice water, so that they have the same
temperature und the voltagedifference will be eliminated. The chart recorder was set to zero (left
side). After that, RANGE was set to 5 mV. Water was put into the sample tube and was heated
using a heatgun until it boiled. At the boilingpoint of water, the chart recorder showed a value of 82
%. After that, the sample tube was put into icewater again and the chart recorder was set to zero at
the right side. The thermovoltage of a freezing mixture was measured.
Mesasurement:
The samples (different mixtures of durene/naphthalene with known molarfraction) were placed in
the sample tube, liquified with a heatgun and cooled down with icewater. For each sample the
measurement was carried out twice (see table 1, appendix). The sample tube was cleaned by
liquifing the sample and rinsing with aceton.
2
5 Results
The phase diagram can be drawn by plotting the measured freezing temperatures versus the
corresponding molar fractions.
Fig. 2: experimental phase diagram, error bars indicate
the difference of the temperaturs for each measurment.
3
To calculate the ideal phase diagram for the system durene/naphthalen we used the linear relation
between melting point of the mixture and melting enthalpy, given by the equations:
T i =
1 −1
1 Rln x i
−
 (1)
T *i m H *i
T j =
1 −1
1 Rln1−x i 
−

(2)
T *j
m H *j
xi, xj: molar fractions of durene/naphtalene
Ti,Tj: melting temperaures at xi, xj
*
Ti , Tj*: melting points of the pure substances
ΔmHi*, ΔmHj*: melting enthalpies
Fig. 3: calculated phase diagram for durene/naphthalene.
The intersection of the two lines is the eutectic point.
Durene
Naphthalene
Melting Enthalpies:
Measured
(20.4  0.4) kJmol-1
(18.9  1.8) kJmol-1
Literature
20.88 kJmol-1 [1]
19.02 kJmol-1 [2]
6 Discussion
The execution of the experiment went well, no problems occurred.
The experimental phase diagram fits well with the calculated ideal phase diagram. The experimental
curve underlies slightly the calculated curve. A resasen could be that the calibration wasn't exact
enough.
At the eutectic point there is a somewhat bigger error bar, the other error bars are all very small.
This means that the reproduction at that molarfraction did not lead to the same temperature.
The obtained melting enthalpies suit with the literature values.
4
7 Literature
[1] Domalski, E.S.; Hearing, E.D., J. Phys. Chem. Ref. Data, 1996, 1.
[2] Syunyaev, Z.I. et. al., Zhur. Prikl. Khim. (Leningrad), 1984, 57, 666-669.
[3] Meister, E. Grundpraktikum Physikalische Chemie: Theorie und Experimente, vdf, Zürich,
2003, S. 53ff.
8 Appendix
Molarfraction
Voltage 1
Temp. 1 Voltage 2
Temp 2
Measurement durene xD
/ (% of 5mV) / °C
/ (% of 5mV)
/ °C
1a
0
65
79.3
1b
0
65
79.3
2a
0.5068593
36
43.92
2b
0.5068593
41.8
50.996
2c
0.5068593
40
48.8
3a
0.10107416
60
73.2
3b
0.10107416
60
73.2
4a
0.20051489
55
67.1
36
43.92
4b
0.20051489
54
65.88
35
42.7
5a
0.30234155
50.8
61.976
37
45.14
5b
0.30234155
51
62.22
37
45.14
6a
0.40198396
43
52.46
37.5
45.75
6b
0.40198396
43
52.46
37.5
45.75
6c
0.40198396
43
52.46
39
47.58
7a
0.60121393
44
53.68
36
43.92
7b
0.60121393
44
53.68
38
46.36
8a
0.70075922
50
61
36
43.92
8b
0.70075922
50
61
35
42.7
9a
0.81158195
55
67.1
9b
0.81158195
55
67.1
10a
0.89931277
59
71.98
10b
0.89931277
59
71.98
11a
1
64
78.08
11b
1
63.5
77.47
Tab. 1: Measured data voltage 1 and voltage 2, calculated temperatures temp. 1 and temp. 2.
Fig. 4: Linear regression to calculate the melting enthaphies according to (1) and (2).
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