Partially Miscible Liquids: Determination of Mutual Solubility of Phenol – Water

December 21, 2008

Physical Chemistry Experiment




A phenol – water solution was used to determine the solubility of two partially miscible liquids.  The group calculated the volume of water required to prepare the following mixtures with volume percentage ranging from 5% to 95% sample at 5% increment using 10mL phenol sample.  The different volume ratios of mixtures prepared were subjected to constant heating and cooling in order to gather the needed temperature necessary for the construction of the mutual solubility curve of Phenol- Water solution.  The critical solution temperatures were determined at 30% Phenol – 70% Water ratio, 64˚C (for single phased region) and 61.8˚C (for double – phased region)…

I. Introduction

Oil and water don’t mix. Pouring 10 mL of olive oil into 10 mL of water results in two distinct layers, clearly separated by a curved meniscus. Each layer has the same volume and essentially the same composition as the original liquids. Because very little mixing has apparently occurred, the liquids are called “immiscible” or unmixable.

Pouring grain alcohol into water results in a single liquid phase. No meniscus forms between the alcohol and the water, and the two liquids are considered “miscible”. Nearly any pair of liquids is miscible if only a trace amount of one of the liquids is present.

Many liquid mixtures fall between these two extremes. Two liquids are “partially miscible” if shaking equal volumes of the liquids together results in a meniscus visible between two layers of liquid, but the volumes of the layers are not identical to the volumes of the liquids originally mixed. For example, shaking water with certain organic acids results in two clearly separate layers, but each layer contains water and acid (with one layer mostly water and the other, rich in acid.)  Liquids tend to be immiscible when attractions between like molecules are much stronger than attractions between mixed pairs. (Logan, 1998)

The objectives of this experiment are 1) to determine the solubility of two partially liquids (phenol – water solution), 2) to construct a mutual solubility for the pair, and 3) to determine their critical solution temperature.

II. Review of Related Literature

Mutual solubility of polymers and properties of their mixtures

“Heats of mixing of polymers with each other have been measured, the behavior of the mixtures of solutions of various polymers has been studied, and the dependence of mechanical properties of polymer mixtures on the ratio of components has been investigated. It has been shown that mixing of polymers with each other is usually an endothermic process and, therefore, leads to formation of macroscopically homogenous, but actually microheterogenous, systems with an extremely high degree of dispersion. These microheterogenous polymer mixtures are formed because of the enormous viscosity of polymer mixtures, which prevents macroscopic separation into phases but does not hinder the considerable mobility of the segments of flexible chain molecules. It has been shown that the dependence of mechanical properties of microheterogenous polymer mixtures on the ratio of polymers in the mixture have sharp maxima or minima which cannot be found in the case of true polymers in polymer solutions. It has been found that the behavior of some polymer pairs is anomalous, in that exothermal mixing is supplemented by separation of the solution mixture into phases and by the appearance of maxima or minima in the dependences of the properties of polymer mixtures on the ratio of polymers in the mixture. This anomaly has been attributed to the effect of loose packing of the molecules of the polymers which show anomalous behavior. It has been shown that, in these systems, there necessarily exists a lower critical temperature of mixing whose value can be decreased by adding low-molecular solvents to the loosely packed polymer. Attention has been drawn to the fact that, although mixing of amorphous polymers should be considered on a thermodynamic basis to be a mutual solution of two liquid phases, the large dimensions and the flexibility of polymer chain molecules require a critical revision of the possibility of formal application of the basis thermodynamic concepts and relations to a theoretical analysis of the behavior of polymer mixtures.” (Slonimski, 1998)

Equations of state for the calculation of fluid-phase equilibria

“Progress in developing equations of state for the calculation of fluid-phase equilibria is reviewed. There are many alternative equations of state capable of calculating the phase equilibria of a divers (Sadus and Song Wei)e range of fluids. A wide range of equations of state from cubic equations for simple molecules to theoretically-based equations for molecular chains is considered. An overview is also given of work on mixing rules that are used to apply equations of state to mixtures. Historically, the development of equations of state has been largely empirical. However, equations of state are being formulated increasingly with the benefit of greater theoretical insights. It is now quite common to use molecular simulation data to test the theoretical basis of equations of state. Many of these theoretically-based equations are capable of providing reliable calculations, particularly for large molecules.” (Sadus and Ya, 2000)

Mutual solubility study for 94.2:5.8 of ethanol to octane with supercritical carbon dioxide solvent

“Solubility data of a mixture containing 94.2% ethanol and 5.8% octane was measured in carbon dioxide solvent using a high-pressure type phase equilibrium apparatus at pressures up to 103.5 bar and at temperature of 75 °C. The results showed that considerable separation was not achieved in this ethanol and octane ratio. However, the experimental data were then compared with the theoretical data which were obtained from two models which are regular solution theory and Redlich-Kwong equation of state. Regular solution theory is employed to each phase by applying activity coefficient expressions. Redlich-Kwong equation of state is employed to the vapor phase and then with applying fugacity coefficient, liquid phase data is obtained. The regular solution theory as a novel model approach has been found to be encouraging for the prediction of phase equilibria solubilities. It concluded that the regular solution theory model could predict two phases equilibrium data better than Redlich-Kwong equation of state.” (Davarnejad et al, 2008)

Solubility, miscibility and their relation to interfacial tension in ternary liquid systems

The terms, miscibility and solubility, are widely used in phase behavior stud (Ayiralam and Rao)ies of multicomponent hydrocarbon systems. The distinction between these two terms appears to be still hazy, leading to their synonymous use in some quarters. Also, the relation of these two thermodynamic properties with interfacial tension has largely remained unexplored. However, recently a new experimental technique of vanishing interfacial tension (VIT) has been reported relating miscibility with interfacial tension in gas-oil systems. Therefore, the objectives of this study are to correlate miscibility and solubility with interfacial tension and to investigate the applicability of the new VIT technique to determine miscibility conditions in ternary fluid systems. For this purpose, a standard ternary liquid system of benzene, ethanol and water was chosen since their phase behavior and solubility data were readily available. The interfacial tensions of benzene in aqueous ethanol at various ethanol enrichments were measured using the drop shape analysis (DSA) and capillary rise techniques.

The experimental results indicate the applicability of VIT technique to determine miscibility conditions for ternary liquid systems as well. Comparison of IFT measurements with solubility data showed a strong mutual relationship between these two properties, in addition to demonstrating a clear distinction between solubility and miscibility. The interfacial tension appears to be independent of solvent-oil ratio in feed, provided that complete equilibration of fluid phases is allowed to incorporate all the mass transfer effects during experimentation. All these experimental observations have immense application in fluid-fluid phase equilibria studies and to determine the miscibility conditions of gas injection improved oil recovery projects.” (Ayiralam et al, 2006)

Heats of mixing of the partially miscible liquid system cyclohexane + methanol

“The molar excess enthalpies of cyclohexane + methanol were systematically measured with a Picker flow microcalorimeter operated in the discontinuous mode at 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15K. Our measurements are higher than the literature data. This work shows that molar excess enthalpies increase with temperatures, an the straight segments of the excess enthalpy curves in the mid region become shorter with increasing temperature. At 323.15K the curve become one of a miscible liquid system, and the position of the maximum value is at X=0.6. In addition, the calorimetric measurement can be used to determine the compositions of two immiscible phases for the binary mixture.” (Dai and Chao, 1985)

III. Methodology

Apparatus and Materials

Phenol Sample

Distilled water

Stirring Rod

Hot plate

200ml beaker

Thermometer (0.1 deg calibration)

1 L Beaker (2pcs)

A.   Preliminaries

Before the experiment, the group calculated the volume of water required to prepare the following mixtures with volume percentage ranging from 5% to 95% sample at 5% increment, using 10mL sample in each proportion.  The calculations should be approved before proceeding.

B.   Experiment Proper

After the preparation of a 95% sample – 5% water volume to volume mixture based on 10mL of the sample, [Caution: All the samples are corrosive while triethylamine is flammable, a lachrymator and readily forms explosive in air] the mixtures was heated in a water bath with mild stirring until the cloudiness in it disappears. Its temperature was noted. It was cooled in a second water bath with mild stirring until the cloudiness appears. Once again, the temperature was noted. This process was repeated until a fairly constant reading was observed for a specific volume ratio mentioned in the preliminaries. Constant temperature was recorded.

IV. Data and Discussion

After the group prepared a 95% phenol -5% water volume to volume mixtures based on 10mL of the sample (see Table I), the mixture was heated in a water bath with mild stirring and recorded its constant temperature until the cloudiness of the solution disappeared and cooled instantly until the cloudiness appears. As shown in Table I, it shows that on 95% phenol – 85% phenol and 5% phenol, there is no significant changes appeared both for heating and cooling of the mixtures due to the concentration of phenol in the solution.  Cloudiness of the solution started to appear at 80% phenol.

Table I: The prepared amount of water needed to add at the given

percentage of Phenol – Water Solution based on 10ml sample

% Phenol by Volume

Volume of Added Water / mL







































Based on the data in Table II, the group constructed the mutual solubility curve for Phenol – Water solution which is important in the determination of the critical temperature of the mixture.  Critical solution temperature is the temperature at which a mixture of two liquids (Phenol and Water for this experiment), immiscible at ordinary temperatures, cease to separate into two distinct phases.  The black line symbolizes the temperature reading of phenol in the hot water bath while the gray line is the temperature reading of phenol in the cold water bath.


On the other hand, the red curve is the polynomial trend line of mixture in the hot water bath in which the solution tends to become in single phased (no cloudiness appeared), while the blue curve is the polynomial trend line of the cooled mixture that tends to start the double phased region (appearance of cloudiness).  The critical temperatures of the solution was located at 30% phenol – 70% water,   64˚C (heating) and 61.8˚C (cooling).

Table II : Constant temperature reading of Phenol – Water Solution at heating and cooling process on 10ml sample.

% Phenol by Volume

Constant Temperature Reading /˚C




no change appeared

no change appeared


no change appeared

no change appeared


no change appeared

no change appeared















































no change appeared

no change appeared

Figure 1. Mutual Solubility Curve of Phenol – Water Solution

V. Conclusion and Recommendation

Throughout the experiment, the critical solution temperature of the solution was 64˚C (heating) and 61.8˚C (cooling) at 30% phenol – 70% water.  There are factors that affect the solubility of the mixtures, the nature of solute and solvent, the temperature and the pressure.

a)      Nature of Solute and Solvent

  • Molecular Size – The larger the molecule o the bigger its molecular weight, the less soluble the substance will be.
  • Polarity – Polar solutes will dissolve polar solvents; Non – polar solute molecules will dissolve non- polar solvents

b)      Temperature

If the solution process absorbs energy, then the solubility will be Increased as the temperature is increased.  If the solution releases energy, then the solubility will Decreased with increasing temperature.

c)       Pressure

If solid and liquid, there is no change in solubility if pressure changes, likewise, in gas, as pressure increased, solubility also increases.

Cloudiness is significant in this experiment for immiscible liquids.  Through cloudiness, we cansay that the substance is still unmix due to the presence of stable emulsion, but when a completely clear solution with no trace of cloudiness, we can assume that the substance is mixed


Ayiralam, Subhash C. and Dandina N. Rao. “Solubility, miscibility and their relation to interfacial tension in ternary liquid systems.” Fluid Phase Equilibria 249.1 (2006): 82-91.

Dai, Ming and Jian-Ping Chao. “Heats of mixing of the partially miscible liquid system cyclohexane + methanol.” Fliuid Phase Equilibria 23.2 (1985): 315-319.

Davarnejad, R, K.M Kassim and A Zainal. “Mutual solubility study for 94.2:5.8 of ethanol to octane with supercritical carbon dioxide solvent.” Journal of the Chinese Institute of Chemical Engineers 39.4 (2008): 343-352.

Logan, R.S. “The Behavior of a Pair of Partially Miscible Liquids.” Chemical Education 75.339 (1998): 206-208.

Sadus, Richard J and Ya Song Wei. “Equations of state for the calculation of fluid-phase equilibria.” AIChE 46.1 (2000): 169-296.

Slonimski, G.L. “Mutual solubility of polymers and properties of their mixtures.” Journal of Polymer Science 30.121 (1958): 625 – 637.



  1. thanks a lot :)))

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