CHM 431 PHYSICAL CHEMISTRY
TITLE
: PHASE EQUILIBRIUM: EUTECTIC SYSTEM
NAME
: NURFADHILAH BINTI JAAFAR
ID NUMBER
: 2016675256
GROUP
: AS 246 3B
LAB PARTNER
: SITI FATIMAH BINTI SHAIKH ABDUL MUNAIM
SUBMITION DATE
: 8TH NOVEMBER 2016
LECTURER’S NAME
: MADAM ZARILA MOHD SHARIFF
TITLE Phase Equilibrium: Eutectic System OBJECTIVES To determine the eutectic temperature and the composition of the eutectic mixture for the naphthalene and p-nitrotoluene system. INTRODUCTION Eutectic system is the simplest kind of system with two solid phases at low temperature which only the pure solid separates out in the cooling mixture. This composition is known as the eutectic composition while the temperature is known as eutectic temperature. Figure 6.1 shows the equilibrium diagram of a tin and lead system. As pure lead is on the extreme right hand side of the diagram its melting point can be read off where either the solid or the liquid line meets the axis, 327 °C. Similarly the melting point of pure tin can is read off the left hand side, 232 oC. The shape of the cooling curve will change when with some tin is added to lead and lower its freezing point. At 250 oC some solid lead starts to form without tin and the curve get fewer steeps. The eutectic mixture has the lowest melting point of any mixture of lead and tin. At eutectic temperature, the eutectic mixture freezes or melt. If the temperature continues to fall, you obviously just move into the region of a mixture of solid lead and solid tin - in other words, all the remaining liquid freezes.
Figure 6.1: Temperature/ composition diagram for tin and lead system at constant pressure.
PROCEDURE 1. 3g of naphthalene was weighed in a boiling tube and was melted by immersing the tube in a hot water bath. 2. The boiling tube was transfer immediately to the conical flask when the solid in the tube has completely melted. The tube was set vertically by using a clamp in the conical flask. 3. The melt in boiling tube was gently stirred with a thermometer and the temperature of the melt was recorded at every minute interval until it completely solidified and temperature remains constant for a few minutes. The temperature was recorded as the freezing point of pure naphthalene. 4. 1g of p-nitrotoluene was added with 3g of naphtelene into the same boiling tube in 1. The tube was immersed in a hot water bath to melt the mixture in the boiling tube. 5. The boiling tube was transferred to a conical flask and the mixture was gently stirred with thermometer. The temperature of the mixture was recorded at every one minute interval until it completely solidifies and the temperature remains constant. 6. The mixture of different composition of naphthalene and p-nitrotoluene was prepared accordance to the composition given in Table 6.1. Each boiling tube was immersed in a hot water bath to melt the mixture and then procedure 5 was repeated for all the mixtures prepared. Table 6.1 Mass of
3
3
3
3
0
1
2
0
1
2
3
3
3
3
0
25
40
50
100
75
60
Naphthalene (g) Mass
of
p-
nitrotoluene %p-nitrotoluene in the mixture
CHEMICALS 1. Naphthalene, C 10H8 2. p-nitroluene, C 7H7NO2
DISCUSSIONS
The freezing point of naphthalene decreases when p-nitrotuluene added to it. This is because p-nitrotoluene increases the boiling point while decreasing the freezing point. The boiling point of solvent can be change with the addition of solutes. The boiling point of reaction mixture will increase and decreasing the freezing point of when p-nitrotoluene is added to naphthalene. Freezing starts for this mixture where the freezing point starts to decrease at 79 oC as the percentage of p-nitrotoluene added to the naphthalene increases. However, the graph does not horizontal yet even though the energy was released to form solid of lead, but it is differ with p-nitrotoluene form. At this point, there is not enough energy released to keep the temperature constant. The temperature does stop falling at 37 oC. Now both naphthalene and p-nitrotoluene are freezing. The temperature continues to fall once everything has solidified. In this experiment, the compositions for both naphthalene and p-nitrotoluene were conducted to see the change on the freezing point start for each reaction. The less amount of p-nitrolouene, added, the smaller the drop in the freezing point of the naphthalene. For mixture that containing only 24.6% of pnitrotoluene , the freezing point of the naphthalene is 48
o
C which that’s where the graph
become suddenly less steep. The graph will start going horizontal that showing both naphthalene and p-nitrotoluene freezing temperature exactly at the same temperature of 49 oC. When the proportion of p-nitrotoluene increasing, the sign of solids naphthalene appear at lower temperature but the final freezing of the whole mixtures still happens at 49 oC. The trend of the graph still continues at the same level until 100% of p-nitrotoluene was added to the lead. At that point, the trend of the graph change. There is just the single horizontal part of the graph where everything is freezing but it is still the mixture. The particular mixture is what we called the eutectic mixture. The eutectic mixture has the lowest melting point (which is, of course, the same as the freezing point) of any mixture of lead and tin. The temperature at which the eutectic mixture freezes or melts is known as the eutectic temperature. This phenomenon that occurs in this experiment is called as freezing point depression which depends on the concentration of solute particles that associated with a colligative property. Colligative properties are those properties of solutions that dependent on the number of dissolved particles in solution but not the identities of the solutes.
There is some possible error that might occur when conducting the experiments. The major source of error in the experiment during the temperature reading as the temperature was not read automatically by a machine, but manually by the experimenter. Furthermore, when the system is not stirred, the whole solution is not in equilibrium which leads to a deviation in temperature reading that eventually leads to super cooling of the system. Although this will eventually be eliminated, however, this could have been prevented if the system was stirred consistently. The recommendation is that an automatic stirrer can be used rather than a manual one.
CONCLUSIONS
In conclusion, the eutectic temperature of naphthalene is 49 oC and the composition of the eutectic mixture for the naphthalene and p-nitrotoluene was determined.
QUESTIONS
1. Define the following terms: a) Component A distinct chemical species in a mixture. The number of components is the least number of different substances required to describe the composition of all phase in the system. b) Phase A homogenous part of a heterogeneous system that is separated from another parts by distinguishable boundary.
c) Triple Point The temperature and pressure at which the vapour, liquid and solid phases of a substance are in equilibrium state.
d) Critical temperature The temperature at which a substance change phase and a point on pressure temperature curve which liquid and vapour are distinguishable and merge to form single phase.
2. Determine the number of components and phase in a) A salt solution Number of components: salt, water (2) Phase: Liquid (1) b) An aqueous solution of potassium chloride and sodium nitrate Number of components: water, potassium chloride, sodium nitrate (3) Phase: liquid (1) c) An aqueous solution of potassium nitrate Number of components: water, potassium nitrate (2) Phase: liquid (1) d) A saturated solution of copper sulphate stored in closed bottle. Number of components: copper sulphate (1) Phase: liquid (1) e) A mixture of ethanol and distilled water. Number of components: ethanol, water (2) Phase: liquid (1)
REFERENCES
1. Clark, J. (2014, January 12). Solid-liquid phase diagrams: Tin and lead. Retrieved November 05, 2016, from http://chemguide.co.uk/physical/phaseeqia/snpb.html 2. Chung, D.L. (2002). Retrieved from the State University of New York at Buffalo,Mechanical
and
Aerospace
Engineering
website:http://www.mae.buffalo.edu/courses/mae381/lecturenote 3. Williams College. “Binary Solid-Liquid PhaseDiagram.” Accessed on October 6, 2010.
