INTRODUCTION

In condition of vapor-liquid equilibrium, a state where the rate of condensation (vapor changing to liquid) equals the rate of evaporation (liquid goes into a vapor phase) on a molecular level.

http://en.wikipedia.org/wiki/Vapor-liquid_equilibrium

The vapor pressure and composition in equilibrium with a solution can yield valuable information regarding the thermodynamic properties of the liquids involved. Raoult’s law relates the vapor pressure of components to the composition of the solution. The law assumes ideal behavior. It gives a simple picture of the situation just as the ideal gas law does. The ideal gas law is very useful as a limiting law. As the interactive forces between molecules and the volume of the molecules approache zero, so the behavior of gases approach the behavior of the ideal gas. Raoult’s law is similar in that it assumes that the physical properties of the components are identical. The more similar the components the more their behavior approaches that described by Raoult’s law.

Using the example of a solution of two liquids, A and B, if no other gases are present the total vapor pressure Ptot above the solution is equal to the sum of the vapor pressures of the two components, PA and PB.

f the two components are very similar, or in the limiting case, differ only in isotopic content, then the vapor pressure of each component will be equal to the vapor pressure of the pure substance Po times the mole fraction in the solution. This is Raoult’s law.

Thus the total pressure above solution of A and B would be

http://tannerm.com/raoult.htm

AZEOTROPE

Each azeotrope has a characteristic boiling point. The boiling point of an azeotrope can be either greater than the boiling point of any of its constituents (a negative azeotrope , or less than the boiling points of any of its constituents (a positive azeotrope). Positive azeotropes are also called minimum boiling mixtures.

A well known example of a positive azeotrope is 95.6% ethanol and 4.4% water (by weight). Ethanol boils at 78.4°C, water boils at 100°C, but the azeotrope boils at 78.1°C, which is lower than either of its constituents. Indeed 78.1°C is the minimum temperature at which any ethanol/water solution can boil. It is true that a positive azeotrope boils at a lower temperature than any other ratio of its constituents. An example of a negative azeotrope is hydrochloric

acid at a concentration of 20.2% hydrogen chloride and 79.8% water (by weight). Hydrogen chloride boils at –84°C and water at 100°C, but the azeotrope boils at 110°C, which is higher than either of its constituents. Indeed 110°C is the maximum temperature at which any hydrochloric acid solution can boil. In general, a negative azeotrope boils at a higher temperature than any other ratio of its constituents. Negative azeotropes are also called maximum boiling mixtures.

Azeotropes consisting of two constituents, such as the two examples above, are called binary azeotropes. Those consisting of three constituents are called ternary azeotropes. Azeotropes of more than three constituents are also known.

high-boiling azeotrope

low-boiling azeotrope

is a complex mixture of hundreds of different hydrocarbon compounds generally having from 3 to 60 carbon atoms per molecule, although there may be small amounts of hydrocarbons outside that range. The refining of crude oil begins with distilling the incoming crude oil in a so-called atmospheric distillation column operating at pressures slightly above atmospheric pressure.

In distilling the crude oil, it is important not to subject the crude oil to temperatures above 370 to 380 °C because the high molecular weight components in the crude oil will undergo

thermal cracking and form petroleum coke at temperatures above that. Formation of coke would result in plugging the tubes in the furnace that heats the feed stream to the crude oil distillation column. Plugging would also occur in the piping from the furnace to the distillation column as well as in the column itself.

http://en.wikipedia.org/wiki/Azeotrope

EXPERIMENTAL METHOD

Equipment Needed:Isopropyl alcohol WaterTest tubes Pasteur pipettes Tube rackHeating mantle100 ml 2-neck round bottom flaskDistillation SetupThermometer

The fractional distillation equipment was set as it was shown in the figure.

The 50 ml of sample was poured into the bottom flask and boiling chips were added.

The heater was around #1. During the heating, the temperature of vapor and liquid were recorded. The first distillate was collected into initial test tube.

Test tube Vı was used to collect second distillate. After collecting second distillate the heat was turned off. System was cooled down.

Test tube V2 was used collect distillate at equilibrium and Vf was used to take liquid remaining at equilibrium.

The refractive indices of IPA, acetone and water were measured.

The refractive indices of liquids in the test tubes were also measured.

The same processes were repeated for the second sample.

RESULTS

Isopropyl alcohol (B.P: 82.4 oC (760 mmHg), density: 0.785 g/cm³(20oC), MW: 60.09 g/mole)Water (B.P:100.0 oC (760 mmHg), density: 0.998 g/cm³ (20oC), MW:18.0153 g/mole)

Soln. RI1 RI2 IPA water IPA water(V/V) (Tcorrected)

at 20C(Tcorrected)

at 20CWeight fraction

Weight fraction

Mole fraction

Mole fraction

%10 1,3395 1,3400 0,080373 0,919627 0,025533 0,974467%20 1,3470 1,3475 0,164329 0,835671 0,055673 0,944327%30 1,3570 1,3570 0,252114 0,747886 0,091789 0,908211%40 1,3610 1,3610 0,343996 0,656004 0,135854 0,864146%50 1,3655 1,3655 0,440269 0,559731 0,19082 0,80918%60 1,3677 1,3677 0,490152 0,509848 0,223737 0,776263%70 1,3695 1,3695 0,541255 0,458745 0,261299 0,738701%80 1,3715 1,3715 0,593625 0,406375 0,304565 0,695435%90 1,3730 1,3730 0,647308 0,352692 0,35494 0,64506%95 1,3745 1,3750 0,702356 0,297644 0,414333 0,585667

Std calibration curve

V/V concentration(%)

weight percent

mole percent

n average

Temperature measured(C)

n at 20(C)

10 8,031882 4,676901 1,3411 24 1,342925 20,7607 12,83056 1,352467 24 1,35426735 29,73733 19,20955 1,358837 23,5 1,36041245 39,13909 26,54011 1,3642 23,5 1,36577555 48,99694 35,0523 1,366667 24 1,36846765 59,34487 45,05688 1,3719 24 1,373770 64,71418 50,74709 1,3673 24 1,369175 70,22037 56,98405 1,371933 24 1,37373380 75,86873 63,85053 1,3732 24 1,37585 81,66483 71,4469 1,3742 24 1,37690 87,61457 79,89609 1,3788 24 1,380695 93,72411 89,35025 1,3785 24 1,3803

Exp data IPA calibration

From the standard calibration curve data, the molar concentration vs. refractive index graph was plotted. The best fit equality of this graph is found

y = 0.0117ln(x) + 1.3839

From the experimental calibration curve data, the molar concentration vs. refractive index graph was plotted. The best fit equality of this graph is found as:

Y=0.0152ln(x) + 1.3096

By giving the refractive index to the y value, x was found as molar concentration. After defining x, it was converted also weight percent:

1,3430 = y = 0.0117ln(x) + 1.3839Lnx = -3,4188X = 0,0328

Weight percent: Mw(IPA)*X/(Mw(IPA)*X+(1-X)*Mw(water)

= 60.09*0,0328/(60.09*0.0328+(1-0,0328)*18,0153) =0.10148(w/w)

SampleTemp (°C) RI (liq) RI (vap)

X ıpa (liq)(n)

X ıpa (vap)(n)

Weight percent(liq)

Weight percent(vap)

1 100,0 1,3360 1,3360 0,0000 0,0000 0 02 96,3 1,3430 1,3520 0,0328 0,0707 0,101481 0,2023543 93,5 1,3540 1,3630 0,0839 0,1810 0,233899 0,4243014 91,0 1,3610 1,3685 0,1525 0,2896 0,375144 0,5762045 88,2 1,3660 1,3720 0,2339 0,3906 0,504508 0,6812826 86,0 1,3700 1,3740 0,3292 0,4634 0,620762 0,7422777 83,6 1,3730 1,3765 0,4254 0,5738 0,711775 0,8178438 81,8 1,3770 1,3780 0,5988 0,6522 0,832731 0,8621789 80,3 1,3790 1,3790 0,7104 0,7104 0,891108 0,89110810 80,5 1,3800 1,3795 0,7738 0,7415 0,919432 0,90535111 81,3 1,3810 1,3800 0,8429 0,7738 0,947069 0,91943212 82,3 1,3820 1,3820 1,0000 1,0000 1 1

Phase(std) (n/n vs. RI)

Phase(std)(w/w vs. RI)

V1     V2     Vf    RI average T(C) Pvap

RI average T(C) Pvap

RI average T(C) Pvap

%75(IPA) 1,378908 82 752,6032 1,376575 83 783,2557 1,37315 25 42,73194%65(IPA) 1,3764 83 783,2557 1,3761 83 783,2557 1,3691 24 40,10272

Experimental values

    75%   65%  X(liq) X(vap) X(liq) X(vap)V1 0,711817 0,704889 0,55198 0,56887V2 0,560298 0,577443 0,538007 0,554469Vf 0,4309 0,024228 0,30482 0,016084

Experimental concentrations