- 40 -ExperimentSimple and Fraction

- 40 -
Experiment
Simple and Fractional Distillation
6
Objectives
1) To separate two miscible liquids using simple and fractional distillation.
2) To compare the efficiencies of simple and fractional distillation.
Introduction
Distillation is a technique widely used in organic chemistry for separating compounds based on differences in their boiling points. Many organic compounds are volatile; that is, they have relatively high vapor pressures and low boiling points. During distillation, such volatile compounds are heated to boiling in one container, called the pot. The vapors produced are then cooled and condensed by passing them through a water-cooled condenser, and collected in a separate container, called the receiver. This technique can be used to remove a volatile solvent from a non-volatile product; or to separate two or more volatile products that have sufficiently different boiling points.
When a liquid is placed in a closed container, some of the molecules evaporate into any unoccupied space in the container. Evaporation, which occurs at temperatures below the boiling point of a compound, involves the transition from liquid to vapor of only those molecules at the liquid surface. Evaporation continues until an equilibrium is reached between molecules entering and leaving the liquid and vapor states. The pressure exerted by these gaseous molecules on the walls of the container is the equilibrium vapor pressure. The magnitude of this vapor pressure depends on the physical characteristics of the compound and increases as temperature increases.
If the liquid is heated to its boiling point, a quite different phenomenon occurs. The boiling point is the temperature at which the vapor pressure of the liquid is equal to the external pressure applied to the surface of the liquid. This external pressure is commonly atmospheric pressure. At the boiling point, bubbles of vapor are produced throughout the liquid, and the vapor pressure inside the bubbles is sufficiently high and allow them to grow in size. The escape of these bubbles results in the characteristic chaotic motion of the liquid identified as boiling.
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Liquid is converted to vapor more rapidly by boiling than by evaporation. If the heating rate is increased, the temperature of the boiling liquid does not change, but the rate at which vapor is produced from the liquid increases. This increase occurs because the energy that is supplied by the increased heating rate is absorbed as more liquid molecules overcome intermolecular interactions and enter the vapor phase.
When a mixture of two or more volatile compounds is heated, the vapor pressure of the mixture equals the sum of the vapor pressures of each compound in the mixture. The magnitude of the vapor pressure exerted by each compound is determined by the vapor pressure of that compound (P0) and the mole fraction of that compound present in the mixture (X). For an ideal two-compound solution, the solution vapor pressure is expressed by Raoult’s law, shown in Equation 1.
PT = X1P10 + X2P20 (Eq.1)
In this equation, PT is the total vapor pressure of the solution, P10 is the vapor pressure of pure compound 1, X1 is the mole fraction of compound 1, P20 is the vapor pressure of pure compound 2, and X2 is the mole fraction of compound 2.
Figure 1 The boiling point of a miscible mixture is between the boiling points of pure compounds
Figure 2 Vaporizing a mixture of cyclohexane and toluene produces a vapor that is enriched in cyclohexane.
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When two liquids form a homogeneous solution, they are said to be miscible. Such a homogeneous mixture will boil at a temperature between the boiling points of the pure compounds. The exact boiling point of the mixture depends upon the relative amounts of the compounds present. Figure 1 shows the relationship between boiling point and composition for a two-compound mixture of cyclohexane and toluene.
When vapor is produced from such a liquid mixture, the composition of the vapor mixture is different from the composition of the liquid mixture, as shown in Figure 2. The vapor contains a larger percentage of the more volatile compound of the mixture, in this case cyclohexane. For example, a liquid composed of 50 percent cyclohexane and 50 percent toluene would boil at 90 °C and yield a vapor composed of 70 percent cyclohexane and 30 percent toluene.
This composition change that accompanies the vaporization process is the basis for the separation of mixtures by distillation. As the vapors produced by the distillation move into the water-cooled condenser, these vapors condense to a liquid, the distillate, which has the same composition as the vapor from which it is formed. The distillate collected in the receiver will contain more of the more volatile compound than the original mixture.
If one compound is much more volatile than the other, the compounds can be separated in one evaporation step. Such a step is called simple distillation and uses an apparatus that consists of only a pot, a distillation head, a condenser, an adapter, and a receiver, as shown in Figure 3.
When the boiling points of two compounds differ by less than 40 °C, they cannot be separated efficiently by simple distillation. Fractional distillation, a process that has the effect of many simple distillations, must be used. A fractional distillation apparatus includes a fractionating column or a Vigruex column placed between the pot and the distilling head, as shown in Figure 4.
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Figure 3 An apparatus for simple distillation
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Figure 4 An apparatus for fractional distillation
Remark
A Vigreux column as shown on the left will be used as a fractionating column during this experiment.
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The vapors generated in the pot rise up the fractionating column and encounter cooler surfaces, upon which they condense. The condensed liquid is then reheated by rising hot vapors and re-vaporizes. This process of condensation and re-vaporization, shown graphically in Figure 5, may occur again and again as the vapors rise up the column.
Figure 5 Each condensation and re-vaporization increases
the concentration of the more volatile compound
Each vaporization is represented by a horizontal line connecting the liquid composition curve to the vapor composition curve. Each condensation is represented by a vertical line connecting the vapor curve to the liquid curve. For example, the 50:50 liquid mixture (A) vaporizes to produce a 30:70 liquid mixture (B). The 30:70 liquid mixture vaporizes to produce a 15:85 vapor mixture (B’), and so on. Each condensation-vaporization results in an increase in the concentration of the more volatile compound.
These composition changes are reflected by a decrease in boiling temperature as the mixture moves up the fractionating column. If the condensation-vaporization is repeated a sufficient number of times, the vapors of the more volatile compound reach the top of the fractionating column in pure form. As these vapors move into the condenser, the compound condenses and is collected as a liquid.
At the same time, the less volatile compound is enriched in the opposite direction. As the condensed liquid falls toward the pot, the pot gradually contains a higher and higher percentage of the less volatile compound. Thus, a separation of the two compounds is achieved.
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Each condensation and vaporization that occurs on a fractionating column is called a theoretical plate. A fractionating column with a large number of theoretical plates can accomplish many condensation-vaporization steps and, therefore, can efficiently separate the compounds in a mixture.
The fractionating column must be positioned vertically so that condensed liquid can drip down through the rising hot vapors. This dripping promotes equilibrium between the liquid and vapor phases, a condition that allows the column to operate at maximum efficiency and provide an optimum separation. An equally important factor affecting separation of the compounds is the distillation rate. If the distillation is conducted too rapidly, liquid-vapor equilibria will not be established in the fractionating column, and poor separation of the compounds will result.
As the liquid boils, a condensation line of vapor can be observed as it moves up the distillation head. Once these vapors reach the thermometer bulb, a dramatic temperature increase is observed. The temperature of the vapors in the distillation head provides information regarding the progress of the distillation. Initially, the vapors are rich in the more volatile compound, and the observed temperature is close to the boiling point of that compound. In a distillation with an efficient separation, the initial temperature remains relatively constant until all of the compound is collected. After the compound with the lower boiling point is completely distilled, the temperature rises sharply as the vapors of the higher-boiling compound reach the thermometer bulb. At this time, the boiling point of the higher-boiling compound is observed as it distills into the receiver.
When no fractionating column is used, or when the fractionating column is inefficient, mixtures of the distilled compounds are incompletely separated. This inefficiency is indicated by a very gradual increase in the temperature measured during the distillation. Samples collected at temperatures between the boiling points of the two compounds will consist of mixtures of the two compounds.
Experimental Procedure
Part A: Simple Distillation
1) Assemble a simple distillation apparatus as shown in Figure 3, using a 50 mL round-bottom flask as the pot and a 25 mL graduated cylinder as the receiver.
2) Place a few boiling chips into the pot.
3) Add 15 mL of cyclohexane and 15 mL of toluene into the pot using a glass funnel, taking care not to spill the chemicals onto the flask heater.
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4) Start the flow of water through the condenser. Ask for approval from your instructor before proceeding to the next step.
5)

ผลลัพธ์ (อังกฤษ) 2:

- 40 -
Experiment
Simple and Fractional Distillation
6
Objectives
1) To Separate Two miscible liquids using Simple and fractional distillation.
2) To compare the Efficiencies of Simple and fractional distillation.
Introduction
Distillation is a Technique widely used in Organic Chemistry for separating compounds based on. differences in their boiling points. Many organic compounds are volatile; that is, they have relatively high vapor pressures and low boiling points. During distillation, such volatile compounds are heated to boiling in one container, called the pot. The vapors produced are then cooled and condensed by passing them through a water-cooled condenser, and collected in a separate container, called the receiver. This technique can be used to remove a volatile solvent from a non-volatile product; or to Separate Two or More volatile products that have different Sufficiently Boiling points.
When a Liquid Container is Placed in a Closed, Some of the molecules evaporate into any Unoccupied Space in the Container. Evaporation, which occurs at temperatures below the boiling point of a compound, involves the transition from liquid to vapor of only those molecules at the liquid surface. Evaporation continues until an equilibrium is reached between molecules entering and leaving the liquid and vapor states. The pressure exerted by these gaseous molecules on the walls of the container is the equilibrium vapor pressure. Vapor pressure depends on the Magnitude of this physical characteristics of the Compound and increases the As Temperature increases.
If the Liquid is heated to ITS Boiling Point, a quite different phenomenon occurs. The boiling point is the temperature at which the vapor pressure of the liquid is equal to the external pressure applied to the surface of the liquid. This external pressure is commonly atmospheric pressure. At the boiling point, bubbles of vapor are produced throughout the liquid, and the vapor pressure inside the bubbles is sufficiently high and allow them to grow in size. Escape the results of these Bubbles in the chaotic characteristic of the Liquid Motion Boiling As identified.
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Liquid is rapidly converted to Vapor More by Boiling than by evaporation. If the heating rate is increased, the temperature of the boiling liquid does not change, but the rate at which vapor is produced from the liquid increases. This increase occurs because the Energy that is supplied by the Increased Heating rate is absorbed As More Liquid molecules overcome intermolecular interactions and Enter the Vapor phase.
When a mixture of Two or More volatile compounds is heated, the Vapor pressure of the mixture equals the Sum. of the vapor pressures of each compound in the mixture. The magnitude of the vapor pressure exerted by each compound is determined by the vapor pressure of that compound (P0) and the mole fraction of that compound present in the mixture (X). Two-Compound for an Ideal Solution, the Solution Vapor pressure is expressed by Raoult's Law, shown in Equation 1.
PT + = X1P10 X2P20 (Eq.1)
In this Equation, PT is the total Vapor pressure of the Solution, is the P10. Vapor pressure of Pure Compound 1, X1 is the Mole fraction of Compound 1, P20 is the Vapor pressure of Pure Compound 2, and X2 is the Mole fraction of Compound 2.
Figure 1 The Boiling Point of a miscible mixture is between the Boiling points. Pure compounds of
Figure 2 vaporizing a mixture of toluene and cyclohexane produces a Vapor that is enriched in cyclohexane.
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When Two liquids form a homogeneous Solution, they are said to be miscible. Such a homogeneous mixture will boil at a temperature between the boiling points of the pure compounds. The exact boiling point of the mixture depends upon the relative amounts of the compounds present. Figure 1 shows the Relationship between Boiling Point and composition for a Two-Compound mixture of cyclohexane and toluene.
When Vapor is produced from such a Liquid mixture, the composition of the Vapor mixture is different from the composition of the Liquid mixture, As shown in. Figure 2. The vapor contains a larger percentage of the more volatile compound of the mixture, in this case cyclohexane. For example, a Liquid composed of 50 percent cyclohexane and 50 percent toluene would boil at 90 ° C and yield a Vapor composed of 70 percent cyclohexane and 30 percent toluene.
This composition Change that accompanies the vaporization Process is the basis for the Separation of mixtures. by distillation. As the vapors produced by the distillation move into the water-cooled condenser, these vapors condense to a liquid, the distillate, which has the same composition as the vapor from which it is formed. Collected in the distillate contain the Receiver Will More of the Compound More volatile than the Original mixture.
If one is much Compound More volatile than the Other, the compounds Can be Separated in Step one evaporation. Such a Step is Called Simple distillation and uses an Apparatus that consists of only a Pot, a distillation Head, a condenser, an Adapter, and a Receiver, As shown in Figure 3.
When the Boiling points of Two compounds differ by Less than 40. ° C, they can not be separated efficiently by simple distillation. Fractional distillation, a process that has the effect of many simple distillations, must be used. A fractional distillation Apparatus includes a fractionating column or a column Vigruex Placed between the Pot and the distilling Head, shown in Figure 4. As
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Figure 3 An Apparatus for Simple distillation
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Figure 4 Apparatus for fractional distillation An
Remark
A Vigreux. As shown on the left column Will be used As a fractionating column during this Experiment.
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The vapors Generated in the Pot rise up the fractionating column and encounter Cooler surfaces, upon which they condense. The condensed liquid is then reheated by rising hot vapors and re-vaporizes. This Process of condensation and re-vaporization, shown graphically in Figure 5, May occur Again and Again As the vapors rise up the column.
Figure 5 Each condensation and re-vaporization increases
the concentration of the More volatile Compound
Each vaporization is represented by a. horizontal line connecting the liquid composition curve to the vapor composition curve. Each condensation is represented by a vertical line connecting the vapor curve to the liquid curve. For example, the 50:50 liquid mixture (A) vaporizes to produce a 30:70 liquid mixture (B). The 30:70 liquid mixture vaporizes to produce a 15:85 vapor mixture (B '), and so on. Each condensation-vaporization results in an increase in the concentration of the Compound More volatile.
These changes are Reflected composition by a Decrease in Boiling Temperature As the mixture moves up the fractionating column. If the condensation-vaporization is repeated a sufficient number of times, the vapors of the more volatile compound reach the top of the fractionating column in pure form. Move As these vapors into the condenser, the Compound condenses and is Collected As a Liquid.
At the Same time, the Less volatile Compound is enriched in the Opposite direction. As the condensed liquid falls toward the pot, the pot gradually contains a higher and higher percentage of the less volatile compound. Thus, a Separation of the Two compounds is achieved.
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Each vaporization and condensation that occurs on a fractionating column is Called a theoretical Plate. A fractionating column with a Large Number of theoretical plates Can condensation-vaporization accomplish many steps and, therefore, the compounds in a mixture Can Separate efficiently.
The fractionating column Vertically Positioned must be so condensed that down Drip Liquid Can Rising Through the hot vapors. This dripping promotes equilibrium between the liquid and vapor phases, a condition that allows the column to operate at maximum efficiency and provide an optimum separation. An equally important factor affecting separation of the compounds is the distillation rate. If the distillation is conducted Too rapidly, Liquid-Vapor equilibria Will not be established in the fractionating column, and poor Separation of the compounds Will Result.
As the Liquid boils, a condensation line of Vapor Can be observed As it moves up the distillation Head. . Once these vapors reach the thermometer bulb, a dramatic temperature increase is observed. The temperature of the vapors in the distillation head provides information regarding the progress of the distillation. Initially, the vapors are rich in the more volatile compound, and the observed temperature is close to the boiling point of that compound. In a distillation with an efficient separation, the initial temperature remains relatively constant until all of the compound is collected. After the compound with the lower boiling point is completely distilled, the temperature rises sharply as the vapors of the higher-boiling compound reach the thermometer bulb. At this time, the Boiling Point of the Higher-Boiling Compound is observed As distills it into the Receiver.
When no fractionating column is used, or when the fractionating column is inefficient, mixtures of the compounds are incompletely Separated distilled. This inefficiency is indicated by a very gradual increase in the temperature measured during the distillation. Samples Collected at temperatures between the Boiling points of the Two compounds Will consist of mixtures of the Two compounds.
Experimental Procedure
Part A: Simple Distillation
1) Assemble a Simple distillation Apparatus As shown in Figure 3, using a 50 mL round-bottom Flask As. the Pot and a 25 mL graduated Cylinder As the Receiver.
2) Place a few Boiling chips into the Pot.
3) Add 15 mL of cyclohexane and 15 mL of toluene into the Pot using a Glass funnel, taking Care not to spill the chemicals. Heater onto the Flask.
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4) Start the Flow of Water Through the condenser. Approval ask for from your instructor before proceeding to the next Step.
5).

ผลลัพธ์ (อังกฤษ) 3:

Experiment
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- 40 Simple and Fractional Distillation


6 Objectives 1) To separate two miscible liquids using simple and. Fractional distillation.
2) To compare the efficiencies of simple and fractional distillation.

, Introduction Distillation Is a technique widely used in organic chemistry for separating compounds based on differences in their boiling points. Many. Organic compounds are volatile;That is they have, relatively high vapor pressures and low boiling points. During distillation such volatile, compounds. Are heated to boiling in, one container called the pot. The vapors produced are then cooled and condensed by passing them. Through a, water-cooled condenser and collected in a separate container called the, receiver.This technique can be used to remove a volatile solvent from a non-volatile product; or to separate two or more volatile. Products that have sufficiently different boiling points.
When a liquid is placed in a, closed container some of the molecules. Evaporate into any unoccupied space in the container. Evaporation which occurs, at temperatures below the boiling point. Of, a compoundInvolves the transition from liquid to vapor of only those molecules at the liquid surface. Evaporation continues until. An equilibrium is reached between molecules entering and leaving the liquid and vapor states. The pressure exerted by these. Gaseous molecules on the walls of the container is the equilibrium vapor pressure.The magnitude of this vapor pressure depends on the physical characteristics of the compound and increases as temperature. Increases.
If the liquid is heated to its, boiling point a quite different phenomenon occurs. The boiling point is the temperature. At which the vapor pressure of the liquid is equal to the external pressure applied to the surface of the liquid.This external pressure is commonly atmospheric pressure. At the, boiling point bubbles of vapor are produced throughout. The liquid and the, vapor pressure inside the bubbles is sufficiently high and allow them to grow in size. The escape of. These bubbles results in the characteristic chaotic motion of the liquid identified as boiling.
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.Liquid is converted to vapor more rapidly by boiling than by evaporation. If the heating rate is increased the temperature,, Of the boiling liquid does, not change but the rate at which vapor is produced from the liquid increases.This increase occurs because the energy that is supplied by the increased heating rate is absorbed as more liquid molecules. Overcome intermolecular interactions and enter the vapor phase.
When a mixture of two or more volatile compounds, is heated. The vapor pressure of the mixture equals the sum of the vapor pressures of each compound in the mixture.The magnitude of the vapor pressure exerted by each compound is determined by the vapor pressure of that compound (P0). And the mole fraction of that compound present in the mixture (X). For an ideal two-compound solution the solution, vapor. Pressure is expressed by Raoult ', s law shown in Equation 1.
PT = X1P10 X2P20 (Eq.1)
In, this equation PT is the total. Vapor pressure of, the solutionP10 is the vapor pressure of pure, compound 1 X1 is the mole fraction of, compound 1 P20 is the vapor pressure of pure. Compound 2 and X2, is the mole fraction of compound 2.
Figure 1 The boiling point of a miscible mixture is between the boiling. Points of pure compounds
Figure 2 Vaporizing a mixture of cyclohexane and toluene produces a vapor that is enriched in cyclohexane.
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.When two liquids form a, homogeneous solution they are said to be miscible. Such a homogeneous mixture will boil at a temperature. Between the boiling points of the pure compounds. The exact boiling point of the mixture depends upon the relative amounts. Of the compounds present.Figure 1 shows the relationship between boiling point and composition for a two-compound mixture of cyclohexane and toluene.
When. Vapor is produced from such a liquid mixture the composition, of the vapor mixture is different from the composition of. The liquid mixture as shown, in Figure 2. The vapor contains a larger percentage of the more volatile compound of, the mixtureIn this case cyclohexane. For example a liquid, composed of 50 percent cyclohexane and 50 percent toluene would boil at 90 ° C. And yield a vapor composed of 70 percent cyclohexane and 30 percent toluene.
This composition change that accompanies the. Vaporization process is the basis for the separation of mixtures by distillation.As the vapors produced by the distillation move into the water-cooled condenser these vapors, condense to, a liquid the. Distillate which has, the same composition as the vapor from which it is formed. The distillate collected in the receiver. Will contain more of the more volatile compound than the original mixture.
If one compound is much more volatile than the. Other.The compounds can be separated in one evaporation step. Such a step is called simple distillation and uses an apparatus. That consists of only a pot a head, distillation, condenser a, adapter an, a, and receiver as shown in Figure 3.
When the. Boiling points of two compounds differ by less than 40 ° C they cannot, be separated efficiently by simple, distillation. Fractional, distillationA process that has the effect of many, simple distillations must be used. A fractional distillation apparatus includes. A fractionating column or a Vigruex column placed between the pot and the distilling head as shown, in Figure 4.
-
- 43 Figure 3 An. Apparatus for simple distillation
-
- 44 Figure 4 An apparatus for fractional Remark distillation

.A Vigreux column as shown on the left will be used as a fractionating column during this experiment.
-
- 45 The vapors. Generated in the pot rise up the fractionating column and encounter, cooler surfaces upon which they condense. The condensed. Liquid is then reheated by rising hot vapors and re-vaporizes. This process of condensation and re-vaporization shown graphically,, In, Figure 5May occur again and again as the vapors rise up the column.
Figure 5 Each condensation and re-vaporization increases
the. Concentration of the more volatile compound
Each vaporization is represented by a horizontal line connecting the liquid. Composition curve to the vapor composition curve. Each condensation is represented by a vertical line connecting the vapor. Curve to the liquid curve.For, example the 50: 50 liquid mixture (A) vaporizes to produce a 30: 70 liquid mixture (B). The 30: 70 liquid mixture vaporizes. To produce a 15: 85 vapor mixture (B '), and so on. Each condensation-vaporization results in an increase in the concentration. Of the more volatile compound.
.These composition changes are reflected by a decrease in boiling temperature as the mixture moves up the fractionating. Column. If the condensation-vaporization is repeated a sufficient number of times the vapors, of the more volatile compound. Reach the top of the fractionating column in pure form. As these vapors move into, the condenser the compound condenses. And is collected as a liquid.
.At the, same time the less volatile compound is enriched in the opposite direction. As the condensed liquid falls toward. The pot the pot, gradually contains a higher and higher percentage of the less volatile compound. Thus a separation, of. The two compounds is achieved.
-
- 46 Each condensation and vaporization that occurs on a fractionating column is called. A theoretical plate.A fractionating column with a large number of theoretical plates can accomplish many condensation-vaporization, steps and. Therefore can efficiently, separate the compounds in a mixture.
The fractionating column must be positioned vertically so. That condensed liquid can drip down through the rising hot vapors. This dripping promotes equilibrium between the liquid. And, vapor phasesA condition that allows the column to operate at maximum efficiency and provide an optimum separation. An equally important. Factor affecting separation of the compounds is the distillation rate. If the distillation is conducted, too rapidly liquid-vapor. Equilibria will not be established in the, fractionating column and poor separation of the compounds will result.
As the. Liquid, boilsA condensation line of vapor can be observed as it moves up the distillation head. Once these vapors reach the thermometer. Bulb a dramatic, temperature increase is observed. The temperature of the vapors in the distillation head provides information. Regarding the progress of the distillation. Initially the vapors, are rich in the more, volatile compoundAnd the observed temperature is close to the boiling point of that compound. In a distillation with an, efficient separation. The initial temperature remains relatively constant until all of the compound is collected. After the compound with the. Lower boiling point is completely distilled the temperature, rises sharply as the vapors of the higher-boiling compound. Reach the thermometer bulb.At, this time the boiling point of the higher-boiling compound is observed as it distills into the receiver.
When no fractionating. Column, is used or when the fractionating column is inefficient mixtures of, the distilled compounds are incompletely, separated. This inefficiency is indicated by a very gradual increase in the temperature measured during the distillation.Samples collected at temperatures between the boiling points of the two compounds will consist of mixtures of the two compounds.
Experimental. Procedure
Part A: Simple Distillation
1) Assemble a simple distillation apparatus as shown in, Figure 3 using a 50 mL round-bottom. Flask as the pot and a 25 mL graduated cylinder as the receiver.
2) Place a few boiling chips into the pot.
.3) Add 15 mL of cyclohexane and 15 mL of toluene into the pot using a, glass funnel taking care not to spill the chemicals. Onto the flask heater.
-
- 47 4) Start the flow of water through the condenser. Ask for approval from your instructor before. Proceeding to the next step.
5).