A Study of Azeotrope and Acetone/Chloroform Liquid-Vapor Phase Diagram free essay sample

A Study of Azeotrope and Acetone/Chloroform Liquid-Vapor Phase Diagram Abstract: Liquid-vapor phase of acetone/chloroform was studied through distilling a series of mixtures with different mole fraction. When the mixtures were boiling, their vapor was condensed through a water column and collected in a receiving container. Refractive index was collected for starting mixture, distillate and residue for each sample. A boiling temperature versus acetone’s mole fraction was constructed to show the liquid-vapor phase diagram. The boiling temperature of azeotrope was determined to be 62. 2oC with the composition of 23% acetone and 77% chloroform. Keyword: liquid-vapor phase, acetone/chloroform mixture, azeotrope INTRODUCTION In an ideal binary mixture, the interactions between two components A and B are equal to each other. The interaction between A-A, A-B, and B-B are the same. Raoult’s law is hold in ideal liquid mixture giving that at a specific temperature, the vapor pressure of a component is proportional to its mole fraction in the mixture. In reality, many binary mixture do not follow Raoult’s law. The actual vapor pressure can be higher or less than what predicted by Raoult’s law and causes positive or negative deviation. For a positive deviation system, A-B interaction are favorable and the boiling temperature curve at different mole fraction gives a maximum. For a negative deviation system, A-B interaction are unfavorable and the boiling temperature curve shows a minimum. At maximum or minimum point on the curve, the composition of the liquid and of the vapor are the same. Such a mixture is called azeotrope. This study focuses on the mixture of acetone and chloroform. To obtain a boiling temperature vs. mole fraction diagram, a series of simple distillation will be performed. Distillation basically means boiling the mixture and the vapor is obtained in a receiving container. The liquid samples will be analyzed by refractive index. In Figure 1, the structure of acetone and chloroform shows that hydrogen bonds will likely be formed in the mixture. Therefore, favorable interactions between two components a positive deviation boiling temperature diagram are expected. EXPERIMENTAL A series of experimental mixture of acetone and chloroform were made as shown in Table 1. Each sample was distilled until obtaining a constant boiling temperature (no or very slow change in temperature when heating). As the mixture was boiled, the vapor was condense through a water column and collected. Refractive Index (RI) was obtained for starting mixture, distillate in receiver container, and residue left over for each sample. RESULT Mole fraction of acetone, boiling temperature and refractive index of starting mixture, distillate and residue are presented in Table 2. Mole fraction of acetone in starting solution was calculated by using density of acetone (0. 791 g/mole) and density of chloroform (1. 492 g/mole) (Sigma-Aldrich). The process of calculation was shown below mole acetone/chloroform = nA,B = Volume? density? 1Molecular Weight mole fraction = nA,BnA+nB The refractive index of starting solution at different mole fraction of acetone was put together in a graph as Figure 2. It was used as a calibration curve to determine the mole fraction of acetone corresponded to each boiling temperature. The equation of calibration curve is y = -0. 0857x + 1. 433 so at an obtained boiling temperature T, the mole fraction of acetone in either distillate or residue was calculated as Mole fraction=(T-1. 4433)/(-0. 0857) A graph of mole fraction of distillate and residue versus boiling temperature was shown together in Figure 3. DISCUSSION The graph of boiling point versus mole fraction of acetone of a liquid-vapor pressure in Figure 3 showed a convex down with a maximum. The shaped of the graph is similar to a positive deviation system where the interaction between components is more favorable due to hydrogen bonding between acetone and chloroform. The maxima of the graph is at 62. 2oC and the mole fraction of acetone is 0. 23. Therefore, the boiling temperature of acetone-chloroform azeotrope is 62. 2oC and its composition is approximately 23% acetone and 77% chloroform. Literature result of other study that had been done on acetone-chloroform binary system shows that the normal boiling temperature of acetone and chloroform are 56. 25oC and 61. 15oC respectively while the boiling temperature of the azeotrope is 64. 45oC. The literature composition of acetone-chloroform azeotrope is 34. 09% of acetone. Although the result of this study was a little bit lower than the literature result, it still represented the properties of a positive deviation liquid-vapor binary phase diagram with the boiling temperature of azeotrope is higher than boiling temperature of pure components. Some sources of error might come from not measuring the exact amount for each component of the mixture or not taking the correct boiling temperature during distillation. Also since this study was dealing with volatile compounds, refractive index reading might be incorrect since the sample was vaporized too quickly. CONCLUSION Azeotrope was studied through a series of prepared acetone-chloroform mixtures with different mole fraction. Distillation was performed to boil the liquid mixture and condense the vapor into a receiver. Thus, it created a binary liquid-vapor phase which was presented in the graph of Figure 1 and Figure 2. The azeotrope boiling temperature is the maximum peak of the graph in Figure 2 and the composition of the azeotrope is 23% acetone and 77% chloroform. The results are in reasonable agreement with literature values of acetone-chloroform mixture. REFERENCE (1) Daniels, F. ; Williams. J. W. Bender, P. ; Alberty, R. A. ; Cornwell, C. D. Experimental Physical Chemistry, 6th ed. ; Mcgraw-Hill Book Company INC: New York, 1962; pp 321-338 (2) Monahan,J. ;Serfis,A. Physical Chemistry Lab Chem 335 (Spring 2013). ; Saint Louis University. Saint Louis, 2013; pp 113-124 (3) Atkins, P. Physical chemistry. W. H. Freeman and Co: New York, 2010. (4) Luyben, W. Control of The Maximum-Boiling Acetone/ Chloroform Azeotropic Distillation System; Industrial amp; Chemistry Engineering Research, 2008. Figure 1. Hydrogen bonding is formed in a binary mixture of acetone and chloroform.