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partially miscible diagram of phenol and water...

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EXPERIMENT 2: PARTIALLY MISCIBLE BINARY LIQUID MIXTURE

PROGRAMME: BSc Environmental and Analytical chemistry DATE: 16/01/19

1. AIM The aim of this experiment is to determine the solubility of two partially miscible liquids and constructing the mutual solubility curve for determination of the critical solution temperature 2. INTRODUCTION Miscibility means how completely 2 or more liquids dissolve in each other, it depends on the forces of attraction between the molecules of the different liquids. Liquids with similar molecular structure (polarity) will likely dissolve in each other. Polarity refers to the extent to which partial positive and negative charges appear on a molecule as a result of the type of arrangement of its atoms. Miscibility is a solubility phenomenon, thus it is affected by factors (1) nature of solute/solvent[composition] (2)temperature and (3)pressure. If the phase rule is applied in this two-phase mixture, two variables are needed to be specified to describe the system completely. The phase rule calculation is shown as P=c −p+ 2 ¿ 2−2+2 ¿2 At constant pressure the remaining significant variables are temperature and composition. The composition is uttered in percent by weight. The temperature of the system can influence the miscibility of the liquids and is dependent on the reaction type i.e. endothermic or exothermic process.[ CITATION Sin05 \l 2057 ]. If endothermic, the solubility of the solution will increase with an increase in temperature. For an exothermic process, solubility will increase with decrease in temperature. For phenol and water, the mutual solubility will increase with an increase in temperature until it reaches a consulate point which is also known as critical solution temperature. Above this point, the components of a mixture are completely miscible and homogenous in all proportions and below that point, the mixture separates into two layers. (Mathur, 2017) A number of different mixtures of phenol and water are prepared and heated until complete miscibility is achieved and as the mixtures cool, two-phase systems form at certain temperatures which are recognisable by the appearance of turbidity (Rubber, no date). Plotting separation temperatures against mole fraction of the mixtures gives the phase diagram.

3. PROCEDURE Seven different boiling tubes were prepared and labelled, then 7 samples of phenol and water samples were prepared as shown from table 1 that was provided. The first phenolwater solution was transferred into a boiling tube and the phenol-water sample transfer process was done in a fume cupboard since phenol is toxic. A thermometer was placed into the test tube then the test tube was sealed using Para film followed by aluminium foil. Precautions were taken so as to ensure that the thermometer is not in contact with the bottom surface of the test tube. The test tube was then heated in an 80 ºC water bath until the phase boundary disappears or the turbid liquid becomes clear, the solution was shaken gently during heating and the temperature at which the turbid liquid becomes clear was recorded. The test tube was then removed from the water bath and allowed to cool under air until the liquid becomes turbid again and the phases separated. The temperature was then recorded. The procedure was repeated for the other solutions (remaining 8 phenol-water sample) to obtain temperature versus mole fraction data. The procedure also was repeated twice for each temperature set (when turbid and when clear) of each solution and the average temperature was taken. The data was then recorded in table 1 provided. 4. RESULTS Sample calculations

Sample 1;phenol mole fraction

mass of phenol MM of phenol ¿ mass of phenol mass of water + MM of phenol MMof water 2.765 g 94.11 g /mol ¿ 17.32 g 2.765 g + 94.11 g/mol 18.02 g /mol = 0.0297

Phenol mole fraction (mol) Vs Temperature 66 64

Temperature C

62 60 58 56 54 52 50 0.03

0.03

0.05

0.08

0.1

0.11

0.17

Phenol Mole Fraction (mol)

Figure 1: A plot of the mole fraction of phenol against average temperature at which turbidity of the solution was obtained

5. DISCUSSION Phase rule is the principle that in any system in equilibrium the number of degree of freedom is equal to the number of components less than the number of phases plus two. It is a useful device for relating the effect of the least number of independent variables, for instance ,concentration, pressure and temperature upon the solid, liquid and gases that can exist in equilibrium system containing a given number of components. The phase rule can be express as F=C-P+2.from the phase it can be gathered that the solubility curve of water in liquid phenol may be obtained, and it is found that the solubility also increases with rise of temperature. It is clear that since, with rise of temperature, the concentration of water in the phenol layer and also of phenol in the water layer increase, the composition of the two conjugate solutions become more and more nearly the same, and at a certain temperature the two solutions become identical in composition. The temperature at which the two layers become identical in composition and are, in fact, one layer is known as the critical solution temperature [CITATION MSi06 \l 2057 ] The critical solution temperature of the phenol-water system obtained from the experiment was found to be 64.4 0C, the experimental value obtained is slightly lower than the literature value of 65-700C [ CITATION NRC28 \l 2057 ].This is due to some errors that might have occurred during the experiment. Such errors include loss of phenol to evaporation due its high volatility.to increase the accuracy of the results the following precautions have to be taken to overcome errors: insuring the absence of impurities by

proper predation of the apparatus, gentle heating of the mixture as well as stirring the mixture while covered to avoid evaporation of phenol. 6. CONCLUSION The critical solution temperature of a mixture of phenol and water was found to be 64.4 0C 7. REFERENCES 1. Atkins Peter, D. P. J., 2002. Atkins' Physical Chemistry. 7th ed. New York: Oxford University Press Inc. 2. council, N. R., 1928. International Critical Tables of Numerical Data, Physics, Chemistry and Technology. New York and London: McGraw-Hill Book Company, Inc. 3. Singh, M., 2006. Upper consolute temperature of water-phenol systems with some additives. Journal of Iranian Chemical Society, III(4), pp. 334-339. 4. Sinko, P. J., 2005. Martin's Physical pharmacy and Pharmaceutical Sciences. 5th ed.

s.l.:Lippincott Williams and wilkins.

5. Mathur, A. 2017. ‘Effect on the Upper Consolute Temperature ( UCT ) of a Partially Miscible Phenol-water Solution with Addition of Ionic Compounds like NaCl , KCl , and Organic Compounds like C 10 H 8 ( Naphthalene ), and C 10 H 16 O ( Camphor ) Producing a Ternary System’, International Journal of Inovation and Reseacrh in Educational Science, 4(3), pp. 2349–5219. 6. Rubber, M. (no date) ‘Chemical equilibrium Solubility diagram of two partially miscible liquids 03 . 05 What you can learn about’, pp. 5–7....