ABSTRACT

Immiscible substances are caused by the solubility properties of liquid. In most cases for liquids, two immiscible liquids cannot mix even with the addition of a tertiary component. But the addition of a highly polar substance demonstrates a change in its solubility. In this experiment, we used butanol, acetic acid and water as tertiary components. We created fourteen (14) mixtures of butanol and acetic acid with different compositions and then they were allowed to achieve thermal equilibrium. Each of them was then titrated with water (at 25C) until permanent turbidity appeared. Refractive indexes were then measured by a refractor and then recorded. Water was then added to the mixture and the mixture was allowed to form separate layers. Refractive indexes were then recorded again for each layer.Using a ternary plot and the gathered data from the earlier parts, we draw the boundary between two-phase and one-phase systems and the corresponding tie lines.

INTRODUCTION

Extraction of constituents by solvent is a very common practice in chemical processing where a mixture containing separable components is treated with a solvent in which one or more of the desired components are preferentially soluble. This type of extraction is called liquid-liquid extraction in which a solution is brought into contact with a second liquid (solvent) essentially immiscible with the first one in order to bring about transfer of one or more components from the solution into the second solvent. It is an effective alternative process to distillation process. Liquid-liquid extraction process is the most useful method for purification, enriching and separation of components of very close volatility and of heat sensitive.In many cases, butanol is found in its aqueous form. Butanol is an important laboratory reagent, thus, the study of butanol extraction from its aqueous solution is fascinating all the time. In this study, in order to find out the proper solvent for the separation of butanol from aqueous solution, phase equilibrium data and mutual solubility data were therefore obtained experimentally by using solvents. Separation factor which is a quantitative index of effectiveness of separation has been computed from these data.Separation process in which a solute in a feed stream is extracted by contacting the feed with a solvent is called solvent extraction. The solute has to be soluble in both the feed and solvent in order for the extraction to take place. The solvent and the feed for industrial extraction operations are normally partially soluble in one another. A ternary system will be formed consists of the feed, solvent and solute. The composition of such a system can be conveniently represented on an equilateral triangle plot with each corner of the triangle presenting one of the three components.The purpose this experiment was carried out was to determine the bimodal curve and the typical tie lines of the water-water-butanol acid system. The points on the bimodal curve was determined using the mass fractions of water, butanol and the other solvent of mixtures after the it was slowly added until a single phase clear solution is obtained. The tie line is drawn using the mass fractions of butanol, water and the other component of mixtures S, with also their mass ratios using trial and error method. Three phase diagram will be drawn in this experiment.

METHODOLOGY

A. CHEMICALS & APPARATUS

For the determination of the solubility curve, the chemicals involve were distilled water, butanol and acetic acid. Standard glass wares were used (beakers and pipettes for transferring chemicals, Erlenmeyer flasks and burettes for the titration).

For the tie lines determination, we used glacial acetic acid, butanol, distilled water and 1.0M NaOH. Same apparatus were used as in first part. Separation of phases had been done by means of separatory funnel. 1.0M NaoH had been prepared by dissolving NaOH pellets in distilled water using a 100mL volumetric flask.

Upon performing the experiment, certain things had to be considered: NaOH when spilled could be irritating to the skin. Proper handling of the apparatus must be observed as well as proper disposal of the waste of chemicals had to be followed in the end of the experiment. When doing the titration, it had to be ensured that you are shaking the flask continuously and carefully observed when turbidity forms and remains for a while and when it disappears. Also, remember to put phenolphthalein indicator when performing the titration in the tie lines determination.

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B. EXPERIMENTAL PROCEDUREPart 1.Determined solubility curve had been done by starting with determining the first two points in the curve which lies on the horizontal axis of the curve. These two points were the solubility of butanol in water and the solubility of water in butanol. The cloudy appearance had been the evidence for both solubility. The other points on the curve were then determined by adding acetic acid in the two-phase mixture until it turns back into one phase. The transition could be observed by the disappearance of turbidity in the stirred solution.

20ml of butanol was placed in an empty Erlenmeyer flask which was weighed before using. It was weighed again once the butanol was poured into it. This had been titrated with distilled water giving a cloudy appearance. Knowing the density of the butanol and water, the mass of butanol and water could be identified. The mass percentages had been used to determine the first point in the curve. This process had been repeated but this time 20ml of water was used. The second point on the curve could now been determined. Starting from 20ml of butanol and 5ml of water placed in a 200ml parafilm-covered Erlenmeyer flask. Acetic acid had been added until turbidity disappears. The volume of acetic acid added was then recorded. Addition of 5ml aliquot of water had been done to the mixture from the previous step and it had been titrated again with acetic acid. It had been continued until 30 ml water had been added. Addition of 10ml of aliquot of water was now used and it had been kept titrated until a total of 110 ml of water had been added. Volume of acetic acid used in every stage had been recorded. Knowing the volume and density of the three liquids, their masses could be computed. Hence, their mass percentages in each stages could be determined. Trial 2 had been done to get the average composition of ternary mixtures. The average composition was then used to plot the points in the curve.

Part2.

In order for the diagram to be completed, a tie lines had been obtained. For this, preparation of two-phase mixtures was needed. These phases had to be separated using separatory funnel. These separated mixtures had to be titrated in order to determine the amount of acid the solutions contained. The prepared 1.0M NaOH was the base used to titrate the aqueous acid containing solutions. The two-phase mixture which had been assigned to our group was prepared by mixing 30ml distilled water, 15ml butanol and 2ml acetic acid. This mixture had been placed in the separatory funnel and it had been allowed to settle for a while. The two separated mixture had been labeled TP2(Top Phase) and LP2(Bottom Phase) respectively. After obtaining two separate mixtures, both had been titrated with 1.0M NaOH. An indicator had been used; Phenolphthalein to see the color change right when the mixtures had been titrated. A pale pink color solution was expected. The volume of the base which had been used to titrate the mixtures were the volume of the acid the mixtures contained. Thus, knowing the volumes and densities of the three liquids involve, the masses of each could now be determined. The mass of the two phases could also be computed which was then used to determine the points for the tie lines. Trial 2 had also been done.

RESULTS AND DISCUSSIONS

Ternary phase diagrams are 3 component systems. Toconstruct a ternary diagramit is necessary to know the three binary systems for the three components. In this experiment the three components are butanol, water, and acetic acid. The sides of the triangle corresponds to the mole percent of each of the components with respect to the other two . The objective of this activity is to be able to come up with a curve which will show the concentration of each components at equilibrium provided that the amount of butanol remains constant.To obtain this, the activity was divided into two parts, the first one was to determine the two ends of the the curve on the side of the butanol and that of water. No acetic acid was present during this time. The points on the curve was determined by titrating the butanol-water system with acetic acid.

A. Solubility of Immiscible Liquids

Table 2-1a Solubility of Butanol in WaterVolume of ButanolVolume of Added WaterMass of ButanolMass of Added Water% Mass Butanol% Mass Water

20 ml3.2 mL16.2 g3.2 g83.5116.49

Table 2-1b Solubility of Water in ButanolVolume of WaterVolume of Added ButanolMass of WaterMass of Added Butanol% Mass Water% Mass Butanol

20 ml3.7 mL20 g3.0 g86.9613.04

B. Determination of Cloud Point

Table 2-2a: Trial 1Mixture #Volume Data (mL)Mass (g)Mass Percent (%)

ButanolWaterAcetic AcidButanolWaterAcetic AcidButanolWaterAcetic Acid

12051.4 mL16.23.01.4771.4622.066.48

220104.0 mL16.210.04.2053.2932.8913.82

320155.4 mL16.215.05.6743.9440.6815.38

420206.2 mL16.220.06.5137.9346.8315.24

520257.1 mL16.225.07.4633.2951.3815.33

620307.9 mL16.230.08.3029.7255.0515.23

720409.4 mL16.240.09.8724.5260.5414.94

8205010.5 mL16.250.011.0320.9864.7414.28

9206011.5 mL16.260.012.0818.3567.9713.68

10207012.6 mL16.270.013.2316.2970.4013.31

11208013.6 mL16.280.014.2814.6672.4112.93

12209014.4 mL16.290.015.1213.3574.1812.46

132010015.2 mL16.2100.015.9612.2675.6712.08

1420110

Table 2-2b: Trial 2Mixture #Volume Data (mL)Mass (g)Mass Percent (%)

ButanolWaterAceticAcidButanolWaterAceticAcidButanolWaterAceticAcid

12051.1 mL16.25.001.15572.4722.375.17

220103.9 mL16.210.004.09553.4733.0113.52

320155.3 mL16.215.005.56544.8640.8015.14

420206.3 mL16.220.006.61537.8446.7115.45

520257.1 mL16.225.007.45533.3051.3815.32

620307.8 mL16.230.008.1929.7855.1615.06

720409.3 mL16.240.009.76524.8660.6414.80

8205010.3 mL16.250.0010.81521.0364.9214.04

9206011.5 mL16.260.0012.07518.3567.8713.68

10207012.6 mL16.270.0013.2316.2970.4013.31

11208013.4 mL16.280.0014.0714.6972.5512.76

12209014.1 mL16.290.0014.80513.3974.3812.24

132010014.8 mL16.210015.5412.3075.9111.80

142011015.2 mL16.211015.9611.4077.3811.23

Table 2-3: Average Composition of Ternary MixturesMass Percent (Average of Two Trials)

ButanolWateracetic

171.96522.2155.825

253.38032.9513.67

344.040.7715.26

437.88546.7715.345

533.29351.3815.325

629.7555.10515.145

724.5460.5914.87

821.00564.8314.16

918.3567.9713.98

1016.2970.4013.31

1114.67572.4812.845

1213.3774.2812.35

1312.2875.7911.94

14

It is a common knowledge that alcohols such as butanol are miscible in water. Truth is, It does at certain concentrations and this was proven by the addition of acetic acid. Upon addition andwhen the solution was stirred, it came to a point that a cloudy/turbid phase appears , this is the transition from one region to another can be observed by appearance (or disappearance) of cloudiness or turbidity in the solution. The turbidity results from scattering of light by the large number of very small oily droplets of the second phase that are produced when the system is stirred. Sometimes it is easier to see this when stopping the stirring briefly.If the three components are mixed to give an overall system composition that falls in the 2-phase region, the system will separate into two phases: a phase rich in water and another rich in 1-butanol. To determine the other points, water was added in 5 ml increment each time turbidity appears. When water is added, the mixture goes back to the one phase region, and each time the cloudiness appears, the point falls in the two-phase region which is below the curve. 14 points was plotted, the end point of the last one became to difficult to recognize, anyhow, those were enought to complete the curve. On the second part of the experiment, tie lines were constructed to validate the precision and accuracy of the curve. A mixture of water, acetic acid, and butanol in different concentrations were prepared. This concentrations all resulted to two-phase after a while. Each phase was then recovered, the lower phase being the water-rich mixture, and the upper phase being the butanol rich mixture. The plot of their -mole fractions fell on each side of the curve, the end point of the tie-line. The mole fractions of each component prior to separating the two phases were also plotted and as expected, it fell below the curve and passes along the tie-line. Fig. 2-1. Mixture 2 composed of 30 mL water, 2 mL Acetic Acid, 15 mLButanol.

Figure 2-2: Ternary phase diagram of wateacetic acid-butanol and tie line constructed from 30 mL water, 2 mL Acetic Acid, 15 mLButanol

As mentioned earlier, the points along the curve shows the mass percentage of the three components at equilibrium, information regarding phase equilibria can be predicted by a simple rule (Gibbs phase rule): f = c p + 2 where c is the number of components and p is the number of phases present in the system. The degrees of freedom f, or variance, gives the number of variables (e.g., pressure, temperature, composition, etc.) that must be given to completely describe the system, or to locate the state of the system on the phase diagram. In this experiment there were 3 components, and creates a two-phase system which gives the value f=3, however the+ 2 in the equation already corresponds to pressure and temperature, so aside from those 2, the other variable that helped in locating the mixture in the diagram is the concentration.

SAMPLE CALCULATIONS

Page 1 of 7

Solubility of Immiscible LiquidsSolubility of Butanol in waterMbutanol = (0.81 g/mL)(20mL) = 16.20 gbutanolMH20 = (1.0 g/mL)(3.2mL) = 3.20 gH2O%Butanolmass= = 83.51%%H2Omass = 100% - 83.51% = 16.49%

Determination of Cloud pointTrial 1, Mixture #1Mbutanol = (0.81 g/mL)(20.0mL) = 16.20 gbutanolMH2O = (1.0 g/mL)(5.0mL) = 5.0 gH2OMacetic = (1.05 g/mL)(1.4mL) = 1.47 gacetic -Mass Percent%butanol = = 71.46%%H2O = = 22.06%%acetic = = 6.48%

Average Composition of Ternary MixturesButanol:%butanol = Acetic Acid:%acetic = Determination of Tie-Lines(Relative Masses of Two-phase systems)Trial 1, Mixture #2Mbutanol = (0.81 g/mL)(15mL) = 12.15 gbutanolMH2O = (1.0 g/mL)(30.0mL) = 30.0 gH2OMacetic = (1.05 g/mL)(2.0mL) = 2.10 gacetic

Solubility of Water in ButanolMbutanol = (0.81 g/mL)(3.7mL) = 3.0 gbutanolMH20 = (1.0 g/mL)(20mL) = 20.0 gH2O%Butanolmass= = 13.04%%H2Omass = 100% - 13.04% = 86.96%

Trial 2, Mixture #1Mbutanol = (0.81 g/mL)(20.0mL) = 16.20 gbutanolMH2O = (1.0 g/mL)(5.0mL) = 5.0 gH2OMaa = (1.05 g/mL)(1.1mL) = 1.155 gaa-Mass Percent%butanol = = 72.47%

%H2O = = 22.37%%acetic = = 5.17%

Water:%H2O =

Determination of Tie-Lines(Titration Data: Composition of Two Phases)Trial 1, Mixture #2nacetic = nNaOH = ()(0.0158 L) = 0.0158 molnacetic = nNaOH = (1 (0.025L) = 0.025 mol%wtacetic,TP2=

CONCLUSION

Through the experiment, the students were able to learn how to determine the bimodal curve and tie lines in checking the composition of the water-butanol-acetic acid system. Based on the results of the experiment, the percentages obtained can be considered accurate and precise due to the closeness of the values. However, certain errors were also present, such as the not so perpendicular eye level on measuring the volumes of liquids, overruns during titration, and differing temperature of the room. It is a wondrous experience to actually prove what is only learned theoretically.

REFERENCES

(9th Edition). Physical Chemistry. Sa P. Akins, & J. de Paula, Physical Chemistry. New York: WH Freeman and Company.Feigenson, G. W., & Buboltz, J. T. (June 6, 2001). Ternary Phase Diagram of Dipalmitoyl-PC/Dilauroyl-PC/Cholesterol: Nanoscopic Domain Formation Driven by Cholesterol. Biophysical Journal, 27752788.(7th Edition). Sa J. M. Smith, H. C. Van Ness, & M. M. Abbott, Introduction to Chemical Engineering THermodynamics. McGraw Hill.