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Analysis of the Deviations from Ideality of a Methanol-Water
System through Functions of Mixing
Sarah Rudy Mark SleeperDavid Watts Tyler Garrett
Executive Summary• Main objective included observing deviations from ideality of a
methanol-water solution through heat of mixing, volume of mixing, and analyses of partial pressures of mixing.
• Accomplished by varying molar fractions of methanol and water.• Used a calorimeter to observe heat outputs for exothermic
reaction.• Used pycnometers to measure mass of liquid and calculate
density changes of solutions.• Provided partial pressures of methanol and water at different
mole fractions.
Introduction• What is an ideal solution?
– Interactions between solute and solvent molecules are the same as those between two identical molecules
• How does this translate to the experiment?– Does not absorb or produce heat– Exhibits volume equal to the sum of the volume of its
separate parts– Displays vapor pressure as a linear function of molar
composition• Extensive properties of a solution are directly proportional to
the size of the system.– X = n1 * X1 + n2 * X2
Heat of Mixing
Experimental• Mixing of methanol and water in order to
observe deviations from ideality.
Water and Methanol
Water and WaterMethanol and Methanol
Experimental (cont’d)• Heat of Mixing
– CSC 2-Drop Calorimeter
Data and Results
Data Acquired
Literature Data: Comparison of Experimental Excess Molar Enthalpies To Simulation Data
Vlcek, L.; Nezbeda, I. Excess Properties Of Aqueous Mixtures Of Methanol: Simple Models Versus Experiment. Journal of Molecular Liquids 2007; pp 161.
Data and Results (cont’d)
• Mixing water and methanol is exothermic.• Deviation from ideality increased as the
solution approached 1:1 ratio of methanol and water.
Modification 1• Objective
– How does varying the starting solution’s temperature affect the heat of mixing?
Modification 1 (cont’d)Heat of Mixing in Methanol and Water Mixtures at Varied Temperature
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Mole Fraction of Water
Heat
of
Mix
ing
[J/m
ol]
25 degrees C
35 degrees C
Ideal
Modification 1(cont’d)• Results
– At the higher temperature, the heat of mixing was closer to the ideal value.
• Explanation– At an elevated temperature, the mixture acts more ideally.
The molecules move faster and therefore have higher energy.
– This also means that more space between the molecules is available. The solution mixes faster and easier than at lower temperatures
Modification 2• Objective
– To show how intermolecular forces affect the ideality of the volume of mixing and heat of mixing.
– To show this, isopropanol was substituted for methanol in the mixture with H2O
Methanol Isopropanol
Modification 2(cont’d)
Water and Isopropanol Mixture Water and Methanol Mixture
Modification 2(cont’d)Affect of Intermolecular forces on Heat of Mixing
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Mole fraction of Water
Heat
of
Mix
ing
[J/m
ol]
Methanol and Water
Isopropanol and Water
Ideal
Modification 2(cont’d)• Results
– The Isopropanol and water mixture proved to be closer to ideal than the mixture of methanol and water.
– Isopropanol and water contain stronger molecular forces than do methanol and water. Isopropanol and water more readily mix making it the more ideal solution
– Isopropanol is more polar
Volume of Mixing
Experimental
• Seven solutions were prepared– Covers a range of mole
ratios
Mole Ratio Methanol
Mole Ratio Water
1 0
.8 .2
.6 .4
.4 .6
.2 .8
Experimental
• Volume of mixing is dependant upon density– Ideal Volume of Mixing:
– Real Volume of Mixing:
d
MXMXV 2211
2
22
1
11
d
MX
d
MXVideal
Experimental
• Pycnometers were used– Allow bubbles to escape– Accurate density measurement
Experimental
• Constant temperature is needed.– Water bath at 25°C was used
• The mass of each solution could then be calculated .
pycnometeremptypycnometerfullsolution MMM
Experimental
• Density of mixture could then be calculated:
Mole Fraction of Water
Density of Solution (g/mL)
0 0.790
0.2 0.846
0.4 0.868
0.6 0.905
0.8 0.942
solution
solutionsolution V
Md
Literature Data: Comparison of Experimental Volume of Mixings to Simulation Data
Partial Pressure of Mixing
Partial Pressure of Mixing
Partial Pressure of Mixing (Cont.)
• Due to the exothermic nature of the mixing, the partial pressure of mixing deviated from ideality.– Because of an increased temperature of the
system, components vaporized to a larger extent than if the solution were ideal.
Conclusion
• The mixing of methanol and water is non-ideal– Heat is evolved upon mixing– Volume upon mixing does not equal the sum of the
volumes of the components– A non-linear relationship was observed between the
partial pressure of methanol and its mole fraction.
• Modifications:– An increase in temperature causes the mixture to behave
more ideally with regards to heat of mixing.– The size of the alcohol effects the ideality of the mixture.
References• 1. McQuarrie, D.A.; Simon, J.D. Physical Chemistry: a Molecular Approach. University
Science Books: Sausalito, CA, 1997; p 638.• 2. Block Diagram Of the CSC Model 4400 Isothermal Microcalorimeter; May 1998; 24
Sept. 2008 <http://www.devicelink.com/mpb/archive/98/05/9805b50a.gif>.• 3. Material Safety Data Sheet; 14 March 2001; Iowa State University; 17 Sept. 2008 <
http://avogadro.chem.iastate.edu/MSDS/Methanol.htm>.• 4. Perrot, Pierre. A to Z of Thermodynamics. Oxford University Press: Oxford, 1998.• 5. Liquid (State of Matter): Endothermic and Exothermic Solutions; Britannica Online
Encyclopedia Website; 1 Oct. 2008 <http://www.britannica.com/EBchecked/topic/343026/liquid>
• 6. Vlcek, L.; Nezbeda, I. Excess Properties Of Aqueous Mixtures Of Methanol: Simple Models Versus Experiment. Journal of Molecular Liquids 2007; pp 131-132, 158-162.
• 7. Harris, Daniel C. Quantitative Chemical Analysis, 7th ed.; W.H. Freeman and Company: New York, 2007; p 65.
• 8. Ideal Solution; Britannica Online Encyclopedia Website; 1 Oct. 2008 <http://www.britannica.com/EBchecked/topic/281790/ideal-solution>.
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