Sunday, 14 December 2014

EXPERIMENT: PHASE DIAGRAM OF TWO COMPONENTS SYSTEM

TITLE: Phase Diagram of Two Component System

OBJECTIVES:
  1.  To measure the miscibility temperatures of water-phenol mixtures of known composition. 
  2. To determine the graphs of phenol composition temperature and the critical solution temperatures. 
  3.  To understand the effect of presence of a third component on the water-phenol critical point.
INTRODUCTION:
          Phenol and water are partially miscible liquids, but here phenol is not really liquid, it is considered as liquid since the addition of first part of water reduces the solid’s melting point under room temperature to produce a liquid-liquid system. It forms a two component systems containing liquid phases.
          Phenol, also known as carbolic acid, hydroxybenzene and phenyl alcohol, is produced at the rate of millions of tons per year, mostly from isopropyl benzene. Phenol is a starting material in the manufacture of plastics and drugs. It was used as an antiseptic in the past. However, phenol is poisonous. The phenol-water mixtures used in this experiment are concentrated and dangerous by contact or ingestion.
          Aqueous phenol solutions are used pharmaceutically. At low and high percentages of phenol, water and phenol mix completely, forming a single liquid phase. However, at intermediate compositions, mixtures of phenol and water will separate into two liquid phases.
          Above the critical temperature, phenol and water are completely miscible. At any temperature below certain critical solution temperature, the compositions for two liquid phases in equilibrium are constant and are not affected by the relative amount of these two phases. These phases are termed conjugate phases. The relative amounts of the two phases vary. The miscibility between two partial miscible liquids is affected by the existence of third component. All systems prepared on a tie line, at equilibrium will separate into phases of constant composition.

APPARATUS :      
Boiling tube, measuring cylinder, water bath, dropper, pipette, thermometer, parafilm  sealed, test tube holder

MATERIALS :
Phenol solution, distilled water 
Phenol solution


Distilled water
PROCEDURE :

  1.  8 boiling tubes are prepared and labelled with A, B, C, D, E, F, G and H.  
  2. Each of the boiling tube is filled with 20ml of phenol and water to produce a phenol                  concentration scale between 8% and 80%.  
    Boiling tube
    A
    B
    C
    D
    E
    F
    G
    H
    Percentage of Phenol (%)
    8
    11
    25
    35
    50
    63
    75
    80
  3. A thermometer is placed in boiling tube A and is fixed in place using parafilm sealed. 
  4. Then, boiling tube A is heated in a water bath and is swirled continuously.
  5. The temperature for boiling tube A at which the turbid liquid becomes clear is observed and        recorded.  
  6. Then, boiling tube A is removed from the water bath and is let to cool until the liquid to become turbid and two layers are separated. The temperature is recorded.
  7. The average temperature of  boiling tube A at which two phases are no longer seen or at which two phases exist is determined.
  8. Steps 3 to 7 are repeated using boiling tube B, C, D, E, F, G and H.
RESULT :           

Boiling tube
Percentage of phenol(%)
Volume of phenol
(ml)
Volume of water
(ml)
Temperature (̊C)
Average temperature(̊C)
Single phase
Two phase
A
8
1.6
18.4
52
45
48.5
B
11
2.2
17.8
62
50
56
C
25
5.0
15.0
64
55
59.5
D
35
7.0
13.0
66
58
62.0
E
50
10.0
10.0
74
65
69.5
F
63
12.6
7.4
77
68
72.5
G
75
15.0
5.0
75
65
70
H
80
16.0
4.0
70
60
65





QUESTION :


  1.  Discuss the diagrams with reference to the phase rule.

The phase rule is a useful device to relate the effect of least number of independent variables such as temperature, pressure and concentration upon the various phases such as solid, liquid and gaseous that can exist in an equilibrium system containing a given number of components.
The phase rule is expressed as :
F = C – P + 2
Where F is the number of degrees of freedom in the system, C is the number of components and P is the number of phases present.
Below the graph, the two component system, which are phenol and water exists as two phase, so the degrees of freedom is
F = C – P +2
   = 2 – 2 + 2
   = 2
This shows that the system has 2 independent variables which is temperature and concentration.
Above the graph, the two component system, which are phenol and water exists as one phase, so the degrees of freedom is
F = C – P + 2
   = 2 – 1 + 3
   = 3
This shows that the system has 3 independent variables which are temperature, concentration and pressure.


2.  Explain the effect of adding foreign substances and show the importance of this effect in pharmacy.

Addition of foreign substances such as salt can affect the critical temperature and the phase separation. The addition of salt will reduce the miscibility of the phenol and water which cause the phase separation. The water molecules will associate with the salt ions and hydrating them. So, the simple ion will lower the tendency of the water to solvate the phenol. Addition of the salt will increase the critical temperature of phenol on phenol rich side of the coexistence of the curve. If the foreign substances are soluble in both liquid, it is called as blending. For example, when succinic acid is added to the water-phenol mixture , succinic acid is soluble or completely miscible in each water and phenol therefore it causes a blending of the liquids making the mixture one phase. The purity of the substances can be determined by the solubility of the substance.

DISCUSSION:
    Miscibility is the property of substances to mix in all proportions, forming a homogeneous solution. The term is most often applied to liquids, but applies also to solids and gases. Water and ethanol, for example, are miscible because they mix in all proportions. By contrast, substances are said to be immiscible if a significant proportion does not form a solution. Otherwise, the substances are considered miscible. For example, phenol is significantly soluble in water, but these two solvents are not miscible because they are not soluble in all proportions.
        A liquid is said to be miscible if it dissolves completely in another liquid and is difficult to separate like alcohol is miscible in water. An immiscible liquid is one which does not dissolve but forms a layer over another liquid and can be separated easily like oil is immiscible in water. If we were to pour a little of an immiscible liquid into a test tube containing water we would see that it forms a thin layer above the water. In organic compounds, the weight percent of hydrocarbon chain often determines the compound's miscibility with water. For example, among the alcohols, ethanol has two carbon atoms and is miscible with water, while  octanol with eight carbons is not. Octanol's immiscibility leads it to be used as a standard for partition equilibria. This is also the case with lipids; the very long carbon chains of lipids cause them almost always to be immiscible with water.
       Simple aldehydes and ketones tend to be miscible with water, because a hydrogen bond can form between the hydrogen atom of a water molecule and the ‘lone pair’ of electrons on the carbonyl oxygen atom. Like any other solubility phenomenon, miscibility depends on the forces of attraction between the molecules of the different liquids. The basic rule is liquids with similar molecular structures, in particular similar polarity, will likely dissolve in each other. Polarity means the extent to which partial positive and negative charges appear on a molecule, because of the type and arrangement of its component atoms. Both water and ethyl alcohol have very polar hydroxyl groups (-OH) on their molecules, and therefore both undergo the strong intermolecular attraction known as "hydrogen bonding." Phenol, on the other hand, is not miscible with water at certain proportion though its molecular structure contains a polar groups, -OH, that would be attracted to the water molecules, it also contain a Hexene ring in which electrons are delocalized in it which make the phenol polarity to be reduced.
          But in this experiment, we are able to view the effects of temperature(T) on the miscibility of different liquids( in this experiment are water and phenol). The experiment was conducted until the turbid liquid had turned into a clear liquid. This is because when the 2 solutions are completely miscible, it will appear as one liquid, which in this case, a clear liquid. In this experiment, different proportion of phenol and water were used to see which of those proportion lead to a miscible or immiscible liquid mixture in the test tube. Some of these proportion causes the mixture to be immiscible but those mixture was able to be changed into a miscible mixture when they are heated to a certain temperature(T).
         Using the second law of Thermodynamics, we can explain why the mixture of water and phenol that are immiscible at certain proportion at room temperature and pressure tend to become more miscible when the temperature rises. Heating a mixture of liquids make it easier for the molecule of the liquids to move between miscible and immiscible state. The Second Law predicts that they will shift to the more disordered, more highly dispersed, and therefore, more probably miscible state. But different proportion of mixture of phenol and water required the solution to be heated to different temperature in order to make them miscible.
          From the graph above, may know that all mixture of water and phenol under the graph are immiscible and all the mixture of the water and phenol above the graph are miscible(with respect to each solutions’ proportion). Moving along the graph(left to right), the concentration of phenol increases. This means that it is moving from a water-rich phase to the phenol-rich phase. The average temperature(T) was lowest(48.5ºC) when the percentage of phenol is 8% and the highest average temperature(T) was when the concentration of phenol was 63% which is at 72.5ºC. All proportional combination of water and phenol above 72.5ºC of temperature are completely miscible and yield a one-phase liquid system.

        But the results obtain from this experiment are not exactly spot on to the theoretical values. This may due to several errors were done while conducting the experiment. An example of these errors are such as not sealing properly the test tube which contain the mixture of both solutions(water and phenol). There is also the over heating of the solutions which leads to the reading recorded(temperature) was way above the actual temperature of which the solution become miscible. Plus, there is also the possibility of not immersing the test tube completely in the water bath(the line of the solution in the test tube are above the water bath), which causes the inefficient heat transfer. Last but not least, during the heating process in the water bath, the solution was not swirled in order to distribute the heat evenly, thus, the heat distribution was not efficient which causes the results(temperature) obtained to be off from the actual value.

CONCLUSION:
When the two-component system’s (in immiscible state of known proportion) temperature rises to its miscible temperature, the liquids will appear as a single phase. Thus from this experiment, the miscible temperature for each composition of phenol and water was able to be determined. They are 52°C for 8% of phenol, 62°C for 11%, 64°C for 25%, 66°C for 35%, 74°C for 50%, 77°C for 63%, 75°C for 75% and 70°C for 80% of phenol.
The graph of phenol’s concentration against the average temperature was plotted and the critical temperature was determined, which is 72.5°C.

REFERENCES :









EXPERIMENT: PHASE DIAGRAM FOR THREE COMPONENTS SYSTEM

TITLE: Determination of Phase Diagram for Ethanol/ Toluene/ Water System Theory

OBJECTIVE: To determine phase diagram for three component system (ethanol/ toluene/ water system theory)

INTRODUCTION:
          Ternary or three-component system is a complex type of multi- component system. Ternary systems are more frequently encountered in practice than binary systems. For example, air is often approximated as being composed of nitrogen, oxygen, and argon, while dry natural gas can be rather crudely approximated as being composed of methane, nitrogen and carbon dioxide. Intuitively, having more than two components poses a problem when a pictorial representation is desired. A rectangular coordinate plot, having only two axes, will no longer suffice. Gibbs first proposed the use of a triangular coordinate system.
         Ternary phase diagrams are three component systems. To construct a ternary diagram it is necessary to know the three binary systems for the three components. Ternary diagrams have a vertical temperature axis. The actual ternary diagram may be represented as a three dimensional form or more commonly as a two dimensional projection of the liquids surface onto the base of the triangle created when the three binary diagrams are joined together. This irregular triangle is often transformed into an equilateral triangle to facilitate presentation and interpretation. In modern times, we use an equilateral triangle for such a representation. Figure 1 shows an example of a ternary phase diagram. Note that the relationship among the concentrations of the components is more complex than that of binary systems.
A
BC

Figure 1

Figure 1 : Three - component triangular representation
Features:
  • Any point within this triangle represents the overall composition of a ternary system at a fixed temperature and pressure. 
  • By convention, the lightest component is located at the apex or top of the triangle (A). The heavy and medium components are placed at the left hand corner (B) and right hand corner (C), respectively. 
  • Every corner represents a pure condition. Hence, at the top we have 100 % B, and at each side, 100 % A and 100 % C, respectively. 
  • Each side of the triangle represents all possible binary combinations of the three components. 
  • On any of those sides, the fraction of the third component is zero (0%). 
  • As you move from one side (0 %) to the 100 % or pure condition, the composition of the given component is increasing gradually and proportionally. At the very center of the triangle, we find 33.33 % of each of the component.
          To differentiate within the two-phase region and single-phase region in the ternary diagram, pressure and temperature must be fixed. There will be different envelopes (binodal curves) at different pressures and temperatures. The binodal curve is the boundary between the two-phase condition and the single-phase condition. Inside the binodal curve or phase envelope, the two phase condition prevails. If we follow the convention given above (lights at the top, heaviest and mediums at the sides), the two-phase region will be found at the top.
          The addition of a third component to a pair of miscible liquids can change their mutual solubility. If this third component is more soluble in one of the two different components the mutual solubility of the liquid pair is decreased. However, if it is soluble in both of the liquids, the mutual solubility is increased. Thus, when ethanol is added to a mixture of benzene and water, the mutual solubility of the liquid pair increased until it reached a point whereby the mixture becomes homogenous. This approach is used in the formulation of solutions. Examples of three component systems that has been studied include castor oil/ alcohol/ water; peppermint oil/ propylene glycol/ water; peppermint oil/ polyethylene glycol/ water.

APPARATUS:
Burette, conical flask, retort stand, measuring cylinder, test tubes

Burette

Conical flask and measuring cylinder
MATERIALS:
Ethanol, Toluene, Water
Ethanol

Toluene
Distilled water

EXPERIMENTAL PROCEDURES:
  1. Mixtures of ethanol and toluene were prepared in sealed containers measuring 100cm3 containing the following percentages of ethanol (in percent): 10, 25, 35, 50, 65, 75, 90 and 95. 
  2. 20ml of each mixture was prepared by filling a certain volume using a burette accurately.  
  3. Each mixture was titrated until cloudiness is observed due to the existence of a second phase. 
     
     
  4. A little water was added and shaken well after each addition.  
  5. The room temperature was measured using the thermometer.   
  6. The percentage based on the volume of each component was calculated when the second phase starts to appear.  
     
  7. The points were plotted onto a triangular paper to give a triple phase diagram at the recorded temperature. One more measurement was done if necessary.
RESULTS:

Ethanol
Toluene
Water
Total volume of Ethanol + Toluene + water (mL)
Volume (mL)
Percentage (%)
Volume (mL)
Percentage (%)
Volume (mL)
Percentage (%)
2
9.26
18
83.33
1.6
7.41
21.6
5
24.04
15
72.12
0.8
3.85
20.8
7
33.82
13
62.80
0.7
3.38
20.7
10
45.87
10
45.87
1.8
8.26
21.8
13
55.56
7
29.91
3.4
14.53
23.4
15
60.00
5
20.00
5.0
20.00
25.0
18
56.25
2
6.25
12.0
37.50
32.0
19
51.21
1
2.70
17.1
46.09
37.1



CALCULATION:
When the second phase start to appear, the percentage components of:

  • 10% ethanol = 2mL ethanol;

% of ethanol = 2mL /(2+18+1.6)mL×100% = 9.26%
% of phenol = 18mL /(2+18+1.6)mL×100% = 83.33%
% of water = 1.6mL /(2+18+1.6)mL×100% = 7.41%

  • 25% ethanol = 5mL ethanol;

% of ethanol=5mL/(5+15+0.8)mL×100%=24.04%
% of phenol=15mL/(5+15+0.8)mL×100%=72.12%
% of water=0.8mL/(5+15+0.8)mL×100%=3.85%

  • 35% ethanol = 7mL ethano;l

% of ethanol=7mL/(7+13+3.7)mL×100%=33.82%
% of phenol=13mL/(7+13+3.7)mL×100%=62.8%
% of ethanol=0.7mL/(7+13+3.7)mL×100%=3.38%

  • 50% ethanol = 10mL ethanol;

% of ethanol=10mL/(10+10+1.8)mL×100%=45.87%
% of phenol=10mL/(10+10+1.8)mL×100%=45.87%
% of water=1.8mL/(10+10+1.8)mL×100%=8.26%

  • 65% ethanol = 13mL ethano;l

% of ethanol=13mL/(13+7+3.4)mL×100%=55.56%
% of phenol=7mL/(13+7+3.4)mL×100%=29.91%
% of water=3.4mL/(13+7+3.4)mL×100%=14.53%

  • 75% ethanol = 15mL ethanol;

% of ethanol=15mL/(15+5+5)mL×100%=60%
% of phenol=5mL/(15+5+5)mL×100%=20%
% of water=5mL/(15+5+5)mL×100%=20%

  • 90% ethanol = 18mL ethanol;

% of ethanol=18mL/(18+2+12)mL×100%=56.25%
% of phenol=2mL/(18+2+12)mL×100%=6.25%
% of water=12mL/(18+2+12)mL×100%=37.5%

  • 95% ethanol = 19mL ethanol;

% of ethanol=19mL/(19+1+17.1)mL×100%=51.21%
% of phenol=1mL/(19+1+17.1)mL×100%=2.7%
% of water=17.1mL/(19+1+17.1)mL×100%=46.09%

DISCUSSIONS:
            The system contains 3 components (ethanol, toluene, and water) but only one phase, F = 3-1+2 =4 for a non-condensed system. The four degrees of freedom are temperature, pressure and the concentrations of two of the three components. Only concentration of two components are required because the sum of these subtracted from the total will give the concentration of the third component. In this experiment, we regard the system as condensed and hold the temperature constant, then F=2. Each of three corners or apexes of the triangle represent 100% by weight of one component A represent for ethanol, B represents water while C represents toluene. As a result, that same apex will represent 0% of the other two components. The three lines joining the corner points represent two-component mixtures of the three possible combinations of A, B and C. Thus the lines AB, BC and CA are used for two-component mixtures .By dividing each line into 100 equal units, the location of a point along the line can be directly related to the per cent concentration of one component in a two-component system. In going along a line bounding the triangle so as to represent the concentration in a two-component system, it does not matter whether we proceed in a clockwise or counter clockwise direction around the triangle, provided we are consistent. The more usual convention is clockwise and has been applied in this experiment. Hence, as we move along A to B, we are signifying systems of A (ethanol) and B (water) containing increasing concentrations of B, and correspondingly smaller amounts of A.
            In this experiment, water and toluene form a two-phase system because they are only slightly miscible while ethanol is completely miscible with both toluene and water. But, as these three components were mixed until certain proportion, all three components would be completely miscible. This experiment is carried out by first making a solution of ethanol and toluene which will be completely miscible and addition of water where at first it will make up two phase. As we continue to add more water until appropriate amount, it will result to one phase system. However when conducting this experiment, we must not clean the apparatus with distilled water so that it will not effect the mixture become cloudy when ethanol and toluene is pour into the apparatus. This is shown in the triple phase diagram that has been plotted on the triangular diagram.
             Addition of water to the mixture of ethanol and toluene increases the mutual solubility of the liquid pair until at one point the mixture become homogenous. The region under the graph shows that there are two phase system form which consist of water and toluene since the solubility of water with toluene is weaker than that with ethanol. Meanwhile the region above the graph shows homogenous mixture.  All the experimental mixtures should all plotted within the triangle theoretically. From the triangle above, the points are deviated a bit from theoretical points which are aligned in parallel line. So, there are might be some errors were occurs when conducting the experiment.
               One of the causes of error is because ethanol and toluene are volatile liquids which can evaporate easily and so they will vaporize as it is left longer and exposed to the air. This caused the measured volume is less than the actual one as some of them already evaporated and thus affected the volume of water needed for titration. Secondly, the cloudiness was hard to be judged because there was no specific range of degree of cloudiness in each of the experiment .This might affect the volume of water added to the system and hence causes deviation of the final result. Next, the eyes of the observer is not perpendicular to the meniscus level of the apparatus so parallax error happened. This caused inaccurate reading or measurement of liquids and thus affecting the curve.  
              Thus to overcome this problem, a few precaution must be taken when doing this experiment to obtain the good result .First of all, the mixtures of ethanol and toluene must be closed immediately with rubber stopper when poured to the conical flask  to avoid  the solution to evaporated. The eye of the observer must be perpendicular to the meniscus of the liquids to avoid parallax error to obtain accurate volume of liquids. Besides that, we have to the same student to observe the cloudiness throughout the experiment so that the results will be more accurate.


QUESTIONS:

1.   Does the mixture containing 70% ethanol, 20% water and 10% toluene (volume) appear clear or does it form 2 layers?

The mixture appear as clear solution

2.     What will happen if you dilute 1 part of the mixture with 4 parts of (a) water (b) toluene (c) ethanol?

(a) water: two phases are formed
(b) toluene: two phases are formed
(c) ethanol: the mixture remains clear

CONCLUSION:
     Phase diagram for ternary systems which contain ethanol/toluene/water is represented using a triangle diagram. The real curve was determined in this experiment. Water and toluene form a two-phase system because they are only slightly miscible. Ethanol is completely miscible with both toluene and water. The rule of the triangle fully explained the three-component system. However, we obtained incomplete binomial curve due to several errors conducted in the experiment.

REFERENCE:
1) http://pubs.acs.org/doi/abs/10.1021/j150093a005
2) http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Phases_of_Matter/Phase_Transitions/Phase_Diagrams