Practical 1: Part A

Practical 1: Phase Diagrams

Part A

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

Three-Component Systems

INTRODUCTION:

           In systems consisting of three components but only one phase, the Phase Rule gives : F=4. The four degrees of freedom are temperature, pressure and the concentrations of any two out of three components. For three component systems at constant temperature and pressure, this composition can be stated in the form of coordinates of an equilateral triangle diagram.

Diagram 1: Ternary phase diagram

           In the above diagram, every corner of the triangular diagram represents a pure component, which 100%A, 100%B and 100%C. Every side of it represents one binary mixture and this triangular diagram represents ternary components. Any line that is parallel to one side of the triangle, shows constant percentage value for one component, for example, the line DE shows 20% A with varies amounts of B and C. It is also the same for the line FG, which shows all mixtures contain 50%B. These lines will intersect one another at K, which surely will contains 20%A, 50%B and 30%c. Measurement can be done like this, because in a shape of equilateral triangle, the total of all distance from point K that are drawn parallel to the three sides of the diagram, are the same, and also equivalent to the length of each from each side of the triangular diagram.

          Addition of one third component into one pair of miscible liquids can change their inter-solubility. If this third component is more soluble in either one from the two components, the inter-solubility of both components will reduce. But if the third component dissolves in both components at the same time, the inter-solubility increases. Thus, when ethanol is added into a mixture of benzene and water, the inter-solubility of both will increase until a point is reached, where the mixture become homogenous. This application can be used in formulizing solutions. Examples of three-component liquid system that have been researched, are castol oil/alcohol/water; permen oil/propylene glycol/water; and permen oil/ polyethylene glycol/water.

          The advantages in preparing an oily substance as a homogeneous aqueous liquid are so clear. However, we should know that what will happen to a system like this, when it is diluted, and this can be explained by comprehension of triangular phase diagram. Diagram 1 is for a system with components permen oil/polysorbitol 20/water. A concentrated solution of 7.5% oil, 42.5% polysorbitol 20 and 50% water (point A in diagram) can be diluted as much as 10 times with water, to give a still-clear solution (now containing 0.75% oil, 4.25% polysorbitol 20 and 95% water). However, when 1ml water is added into 10ml clear B solution (49% oil, 50% polysorbitol 20 and 1% water), the solution turns cloudy, point B’ (44.55% oil, 45.45% polysorbitol 20and 10% water). Consecutively, if 1ml of water is added, the solution becomes clear, point B” (40.5% oil, 41.3% polysorbitol 20, 18.2% water), but if the original solution is diluted to 3 times (16 1/3 oil, 16 1/3 polysobitol 20, 67% water), the solution become cloudy.

OBJECTIVE:
To identify the phase diagram for ethanol/toluene/water system  

APPARATUS:
Sealed test tube, burette, measuring cylinder, 50 ml beaker

MATERIALS: 
 Ethanol, toluene, distilled water

EXPERIMENTAL PROCEDURES:

1) The mixtures of ethanol and toluene are prepared in sealed containers measuring 100 cm3 containing the following percentages of ethanol which are 10 %, 25 %, 35 %, 50 %, 65 %, 75 %, 90 %, and 95 %. 

2) 20 mL of each mixture is prepared by filling a certain volume using a burette accurately.

3) Each mixture is titrated with water until cloudiness is observed due to the existence of second phase.

 

4) A little water is added and shook well after each addition.

5) The room temperature is measured.

6) The percentage is calculated based on the volume of each component when the second phase starts to appear.

7) The points are plotted onto a triangular paper to give a triple phase diagram at the recorded temperature.   

RESULTS:

Table 1:

% of ethanol (v/v)	Volume of Water Used (ml)		Average
	Titration 1	Titration 2
10	1.8	1.9	1.85
25	1.5	1.7	1.60
35	1.1	1.2	1.15
50	1.0	1.0	1.10
65	3.2	3.6	3.40
75	4.6	5.2	4.90
90	14.0	15.4	14.70
95	21.0	23.0	22.0

Table 2:

Total volume	Water	Percentage (%)	Toluene	Percentage (%)	Ethanol	Percentage (%)
(X+20ml)	Volume (ml)		Volume (ml)		Volume (ml)
21.85	1.85	8.5	18.0	82.4	2.0	9.2
21.60	1.60	7.4	15.0	69.4	5.0	23.1
21.15	1.15	5.4	13.0	61.5	7.0	33.1
21.10	1.10	5.2	10.0	47.4	10.0	47.4
23.40	3.40	14.5	7.0	29.9	13.0	55.6
24.90	4.90	19.7	5.0	20.1	15.0	60.2
34.70	14.70	42.4	2.0	5.8	18.0	51.9
42.0	22.0	52.4	1.0	2.4	19.0	45.2

 

Graph of triple phase diagram at the recorded temperature:

PRACTICE:

1. Does the mixture containing 70% ethanol, 20% water and  10% toluene look clear or form 2  phases?

The solution appears clear.

2. What will happen if you dilute1 part of the mixture with 4 parts of (a) water (b) toluene (c) ethanol?

Assume that 1 part of solution = 100mL

So, 4 parts = 400mL

(a) Original volume:  70% ethanol = 70mL

                                   20% water    = 20mL

                                      10% toluene = 10m 

                                   (Total volume = 100mL)

 

After dilution with 400mL water,

70%ethanol= 14%

20% water = 84%

10% toluene = 2 %

(Total volume = 500mL)

From the graph, the point A is inside two liquid phase, hence cloudy solution is formed

(b) Original volume:  70% ethanol = 70mL

                                   20% water = 20mL

                                   10% toluene =10mL

                                   (Total volume = 100mL)

After dilution with 400mL toluene,

70%ethanol = 14%

20%water = 4%

10%toluene = 82%  

(Total volume = 500mL)

From the graph, point B is inside the two liquid phase, hence cloudy solution is formed.

(c) Original volume:   70%ethanol = 70mL

                                    20%water = 20mL
                                    10%toluene= 10mL
                                    (Total volume = 100mL)

After dilution with 400mL of 70%ethanol,
70% ethanol = 94%
20% water= 4%
10% toluene= 2%
(Total volume = 500mL)

From the graph, point C is outside the two liquid phase, locating single, hence clear solution is seen.

DISCUSSION:  
      

          The experiment was carried out to identify the phase diagram for ethanol, toluene and water system. Since we are dealing with a three-componenets system, it is more convenient to use triangular coordinate graph paper, although it is possible to use rectangular coordinates. Originally, toluene was insoluble to water but soluble to ethanol. However, in this experiment, as the three components were mixed until certain proportion, they would be completely miscible.

          First of all, the ethanol were mixed with toluene because they are miscible, then followed by the addition of water. At first, the addition of water to the mixture of ethanol and toluene creates a two liquid phase. However, as we continue adding more water to the mixture until certain proportion, it will result as single liquid phase. This is because the mutual solubilty of the liquid pair increases as the water added to the mixture of ethanol and toluene until the mixture become homogenous.

          From the data of our experiment, the plotted graph (A, B, C, D, E, F, G and H) inside the triangular diagram formed a binomial curve. The region bounded by the curve shows the present of two liquid phases. Inside this regions, the mixture is cloudy. The cloudy solutions formed indicates the phase separation, this is due to the insufficient amount of ethanol to produce a homogenous mixture. When the amount of ethanol is high, it will acts as surfactant which allow the two liquid phases become single liquid phase. Meanwhile, the single liquid phase of homogenous solution was shown at the region above the curve.

          From this experiment, it is proved that ethanol helps to increase the miscibility of the two other components and the homogenity was break by adding more water. This is because, the percentage of ethanol was higher than the percentage of toluene, and also the amount of water needed until cloudiness observed is higher.

          When conducting this experiment, there are few precaution steps that need to be taken a serious considerate in order to get a better result such as : 

1. remove the impurities from the glassware by rinsing them cleanly. 

2. carefully taking the reading of solutions by avoiding the parallax error. 

3. use the consistent rate of agitation for each mixture. 

CONCLUSION:

The experiment of ternary system involve three different liquids which are ethanol, toluene, and water. This ternary system were represent in the form of triangular diagram. The data obtained from the experiment of mixing the ethanol and toluene and then triturated with water is the percentage of ethanol was much more higher than the percentage of toluene and higher amount of water was needed to achieve cloudiness. The two phase system was established once the cloudiness was observed. The single liquid phase formed when toluene and water partially miscible and the ethanol in a sufficient amount. The presence of ethanol help to increase the miscibility of toluene and water. Lastly, when water added exceed the theoritical percentage where the three components are partially miscible, the two phase system occur. 

REFERENCES:

1. A.T.Florence, D. Attwoo, Physicochemical Principles of Pharmacy, 4th edition, 2006, Macmillan   Press Ltd. 

2. http://www.csun.edu/~jeloranta/CHEM355L/experiment5.pdf 

3. Physical Pharmacy: Physical Chemistry Principles in Pharmaceutical Sciences, byMartin, A.N.