1/17/2015 1 experiment – simple & fractional distillation evaluation of the relative...

1/17/2015 1

Experiment – Simple & Fractional Distillation

Evaluation of the relative effectiveness of Simple & Fractional Distillation to separate mixtures of organic compounds based on differences in Boiling Point

Determination of Mole % from Distillate Volume Data, Gas Chromatography, and Refractive Index

Text References

Slayden p. 39-41, 43-46, 47

Pavia - Tech 14.1 - 14.3; p. 719 – 729 (Simple Distillation)

Pavia - Tech 15.1 - 15.6; p. 729 – 740 (Fractional distillation)

Pavia - Tech 22.1 22.12; p. 817 – 836 (Gas Chromatography)

Pavia - Tech 24; p. 845 – 850 (Refractive Index)

Simple & Fractional Distillation

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Overview A mixture of Ethyl Acetate and Butyl Acetate

(unknown mole %) will be subjected to both a Simple Distillation and a Fractional Distillation (using a Vigreux Fractionation Column)

Each distillation will result in three (3) vials (fractions) of distillate representing 3 temperature ranges (0-95oC; 95 -105oC; and 105-130oC)

Volume recovery of total distillate as well as volume recovery of the distillate fractions will be computed

Fractions 1 & 2 will be combined mathematically and assumed to be Ethyl Acetate

Fraction 3 will be assumed to be Butyl Acetate


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Overview (con’t) From the volumes and respective densities, the mass,

moles, mole fraction, and mole % will be computed. Gas Chromatograms of the 6 distillate vials (3 from

Simple Distillation & 3 from Fractional Distillation) plus the original unfractionated mixture will be obtained Mole % of the components in each fraction will be

computed based on the relationship between peak area (readjusted for non-linear thermal response) and mole content

If directed by instructor, Mole % values will also be determined from a standard Regression Curve relating Refractive Index of known mixtures of Ethyl & Butyl Acetate to the measured Refractive Index values of the distillate fractions

Distillation results and mole % values will be used to evaluate the relative effectiveness of component separation by Simple Distillation vs Fractional Distillation


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Vapor Pressure / Boiling Point

According to Kinetic Theory, the molecules in a liquid are in a constant state of thermal motion and some of these molecules are moving fast enough to escape from the liquid forming a vapor above the liquid. This vapor exerts a pressure on the surface of the liquid, i.e., Vapor Pressure

Vapor Pressure – The pressure of the vapor coexisting with a confined liquid or solid, i.e., the pressure in an evacuated container containing a liquid at constant temperature after the liquid and escaping molecules near the surface of the liquid – the vapor - reach equilibrium

The Vapor Pressure of a liquid increases, generally exponentially, with temperature

Boiling Point – As a liquid is heated, the vapor pressure of the liquid increases to the point at which it just equals the applied pressure - usually atmospheric pressure. The liquid now begins to bubble (boil)


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Vapor Pressure / Boiling Point Boiling Point

The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure.At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquidThe standard boiling point is now (as of 1982) defined by IUPAC as the temperature at which boiling occurs under a pressure of 1 bar1 bar = 105 Pascals = 0.98692 atmospheres (atm) = 14.5038 psi (pounds per square inch) = 29.53 in Hg (inches of mercury) = 750.06 mm


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Distillation / Boiling Point Measurement

Note: The temperature range you obtain for your boiling point may be inaccurate for three (3) reasons

1. The atmospheric pressure in the lab may not be:

1 bar (0.98692 atm)

2. The thermometers used in the lab may not reflect the actual temperature

3. The thermal inefficiency of the glassware used for the boiling point determination may result in a

lower than expected measured value by as much as 2 – 5oC

You should take this potential temperature differential into account when you compare your measured results with the list of possible unknowns in lab manual tables


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Vapor Pressure / Boiling Point (Con’t) Different liquid compounds or mixtures of liquids

have different vapor pressures at a given temperature

Liquids with high vapor pressures (Volatile compounds) require relatively little energy (heat) to increase the vapor pressure to match the applied (atmospheric) pressure, and thus, boil, i.e. they have low boiling points

Liquids with low vapor pressures require considerably more energy to increase the vapor pressure to the point where it matches the applied pressure, thus, they have relatively high boiling points

The individual compounds in a mixture each exert its own pressure – partial pressure

The sum of the partial pressures equals to the total vapor pressure of the solution


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Raoult’s Law

In a solution of two miscible liquids (A & B) the partial pressure of component “A” (PA) in the solution equals the partial pressure of pure “A” (PA

o) times its mole fraction (NA)

Partial Pressure of A in solution = PA = (PAo) x (NA)

Partial Pressure of B in solution = PB = (PBo) x (NB)

When the total pressure (sum of the partial pressures) is equal to or greater than the applied pressure, normally Atmospheric Pressure (760 mm Hg), the solution boils

Ptotal = PA + PB = PAo NA + PB

o NB

If the sum of the two partial pressures of the two compounds in a mixture is less than the applied pressure, the mixture will not boil. The solution must be heated until the combined vapor pressure equals the applied pressure


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Raoult’s Law (Con’t) Example

Consider a solution at 100 oC where NA = 0.5 and NB = 0.5

What is the Partial Pressure of A in the solution if the Vapor Pressure of Pure A at 100 oC is 1020 mm Hg?

Ans: PA = PoANA = (1020) * (0.5) = 510 mm Hg

What is the Partial Pressure of B in the solution if the Vapor Pressure of Pure B at 100 oC is 500 mm Hg?

Ans: PB = PoBNB = (500) * (0.5) = 250 mm Hg

Would the solution boil at atmospheric pressure (760 mm Hg)?

Ans: Yes Ptotal = PA + PB = (510 + 250) = 760 mm Hg

What is the composition of the Vapor at the Boiling Point?

Ans: The mole fraction of each would be:NA (vapor) = PA / Ptotal= 510/760 = 0.67

NB (Vapor) = PB / Ptotal= 250/760 = 0.33


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Distillation

Process of vaporizing a liquid, condensing the vapor, and collecting the condensate in another container

Uses of Distillation

Separating liquids with different boiling points

Purifying a liquid.

Distillation Methods

Simple

Vacuum (at reduced pressure)

Fractional

Steam


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Distillation (Con’t)

Pure Substance

Temperature remains constant during distillation process so long as both vapor and liquid are present

Miscible Liquid Mixture

Temperature increases throughout process because composition of vapor changes continuously

Composition of vapor in equilibrium with the heated liquid is different from the composition of the liquid


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Simple Distillation Single Vaporization / Condensation cycle of a

mixture that produces a distillate that is always impure at any temperature range between the range of boiling points of the components

Therefore, it is impossible to completely separate the components in a mixture with Simple Distillation

Relatively pure substances can be obtained from a mixture with Simple Distillation if the boiling points of the components differ by a large amount (>100oC)

If a small increment of the initial distillate is separated and redistilled and this process is repeated many times, effectively producing multiple sequential Vaporization/ Condensation Cycles, an increasingly pure solution can be attained. This would be a very tedious process involving a large number of distillations


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Fractional Distillation Accomplishes the same thing as Multiple Simple

Sequential Vaporization / Condensation Cycles, by inserting a Fractionating Column (a Vigreux Column) between the Distillation Flask and the Distillation Head

The Fractionating Column, of which there are many types containing a variety of packing materials, subjects the mixture to many Vaporization/Condensation Cycles as the material moves up the column toward the Distillation Head, which is attached to the Condenser

With each cycle within the column, the composition of the vapor is progressively enriched in the lower boiling liquid

This process continues until most of the lower boiling compound is removed from the original mixture and condensed in the receiving flask


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Fractional Distillation (Con’t)

When the lower boiling liquid is effectively removed from the original mixture, the temperature rises and a second fraction containing some of both compounds is produced

As the temperature approaches the boiling point of the higher boiling point compound, the distillate condensing into the third receiving flask is increasingly pure in the higher boiling point compound


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Fractional Distillation (Con’t)


As the distillation proceeds, the composition of the liquid and the vapor are continuously changing

The Horizontal and Vertical Lines represent the processes that occur during a fractional distillation.

Each Horizontal Line (L3V3, L2,V2), etc., represents both the vaporization step of a given vaporization/condensation step and the composition of the vapor in equilibrium with the liquid at a given temperature.

Examples:

At 53oC with a liquid composition of 80% A

and 20% B (L4V4 on the diagram), the vapor would have 95% A and 5% B when equilibrium has been established between the liquid and the vapor.

At 63oC with a 50/50 liquid mixture of A&B

(L3V3 on the diagram), the vapor would have a composition of 80% A & 20% B at equilibrium.

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Column Efficiency - How pure can you get!! A common measure of the efficiency of a

Fractionation Column is given by its number of Theoretical Plates

One Theoretical Plate is equivalent to a Simple Distillation, i.e., one Vaporization / Condensation Cycle

The smaller the boiling point difference, the greater the number of theoretical plates a fractionating column must have to achieve separation of mixtures


Boiling Point Number ofDifference Theoretical Plates

108 1 54 3 20 10 7 30

4 50 2 100

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Distillation Equipment SetupNote: Equipment used in distillation experiment is

expensiveUse care to avoid breakage

ASK BEFORE YOU ACT!! Equipment

Heating Block (or sand bath) & Heating Plate

50 mL round bottom Distilling Flask (with boiling chip)

Distillation Head

Thermometer & Thermometer Adapter

Vigreux Fractionation Column (second group only)

Aluminum foil for Vigreux Column & Distillation Head

Water Jacket Condenser (with rubber tubing for water)

Receiving containers – 2 10 mL graduated cylinders & 6 labeled vials with sealing caps


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Distillation Equipment Setup (Con’t) Use 2 ring stands to support apparatus.

Attach clamp to Ring Stand & the Condenser Attach clamp to other Ring Stand & Distillation

Head Use Blue Plastic Clamp to secure Water Jacket

Condenser to neck of Distillation Head Use Blue Plastic Clamp to secure Distillation Head

(or Vigreaux Column) to Distillation Flask Insert thermometer through adapter so that the

bulb is positioned ¼ inch below opening to the Condenser

NOTE: Wrap the Distillation Head, Vigreux Column, and Distillation Flask in Aluminum foil to improve heat insulation


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Elements of The Experiment

Two Distillations

Simple Distillation

Fractional Distillation with Vigreux Column

Work in groups of 4 (2 groups of 2 each)

First group - Simple Distillation

Second group - Fractional Distillation

Each group of 4 will share data, but reports will be written independently

Each report must contain all of the raw data from the group, i.e., from both distillations


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Elements of The Experiment (Con’t)

Simple and Fractional distillations

Note: Can be setup as a single (1) procedure

Note: In Procedure Description make note of addition of the Vigreux column used in the Fractional Distillation

Construct Barchart of incremental volumes (y-axes) vs temperature ranges (x-axes)

For both Simple Distillation & Fractional Distillation:

Determine Total volume recovered

Compute Percent volume recovered

Total Volume in temperature ranges

0 – 95 oC; 95 – 105 oC; 105 – 130 oC

Compute % volume recovered in each fraction


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Combine the volumes from the 1st & 2nd fractions and refer to it as “Fraction A”

Assume the combined 1st & 2nd fractions (fraction A) is Ethyl Acetate and the 3rd fraction (fraction B) is Butyl Acetate

Determine the mass of each compound in fraction A and in fraction B from their respective volumes and density

Compute the Moles of each compound in fraction A and fraction B

Determine the total moles in each fraction

Compute mole fraction

Compute mole %


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Data Collection Place 20 mL of mixture in a 50 mL round bottom flask Set Hot Plate setting to about 5 Use 10 mL graduated cylinder to collect distillate Collect distillate in 5 degree increments recording the

incremental volume collected in the 5 degree intervalNote: 1st increment is from 0oC – 65oC

Continue to collect incremental volumes in 5 degree increments, until temperature reaches 95oC

Transfer the total volume collected in the graduated cylinder up to 95oC to the first labeled vial

Continue to collect distillate in 5 degree increments from 95oC to 105oC

Transfer the total volume collected between95oC - 105oC into the second labeled vial


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Data Collection (Con’t)

Increase temperature setting of Hot Plate

Continue to collect 5 degree volume increments in the graduated cylinder until 1 mL remains in the flask

Note: DO NOT DISTILL TO DRYNESS

Turn off heat

Allow liquid in Distillation Head & Vigreux column to cool and drain into the Distillation Flask (Pot Residue)

Transfer the Pot Residue to the graduated cylinder

Determine the volume of Pot Residue

Transfer the contents of the graduated cylinder to the third labeled vial


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Data Collection (Con’t)

Suggested Table Template For Distillation Data


Simple Fractional

Temp Range Volume (mL) Volume (mL)

0-65 oC

65-70 oC

70-75 oC

75-80 oC

80-85 oC

85-90 oC

90-95 oC

95-100 oC

100-105 oC

105-110 oC

110-115 oC

115-120 oC

120-125 oC

125-130 oC

Pot Residue

Initial Volume

Total Volume Recovered

Incremental Volumes

For each 5 oC temperature interval, record the volume of distillate collected in that temperature range.

Cumulative Volumes for the 0 – 95 oC, 95 – 105 oC, and the 105 - 130 oC fractions, can be computed by summing the incremental volumes for each fraction.

Pot Residue

Pot Residue is the volume of undistilled sample remaining in the Distillation Flask after the Hot Plate is turned off.

Allow the apparatus to cool down; then transfer the remaining liquid in the Distillation Flask to the Graduated Cylinder.

The Pot Residue becomes part of the final increment of Distillate.

Vial #1

Vial #2

Vial #3

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Results

NOTE: The following data analysis scheme is to be applied separately to both the Simple and

Fractional data

First Vial - All the distillate up to 95oC

(Mainly Ethyl Acetate – B.P. - 77.1oC)

Second Vial - All the distillate collected between 95-105oC

Third Vial - All distillate above 105oC

(Mainly Butyl Acetate – B.P. 126.1oC)


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Results (Con’t)

1. Calculate the total volume of distillate recovered

2. Calculate the % Recovery of the distillate

(Total Final Volume / Initial Volume) x 100

3. Use Excel to plot a bar chart of temperature increments on the x-axis and volume increments on the y-axis

Note: First increment is 0 – 65oC

Draw perpendicular lines to the 95 & 110 degree marks on the x-axis


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Example BarChart


1st Fraction

3rd Fraction

2nd

Fraction

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Results (Con’t)

4. Calculate the total volume to the left of the95 oC line (1st fraction)Calculate the total volume in the zone between95 & 105 oC (2nd fraction)Calculate the total volume to the right of the105 oC line (3rd fraction)

5. Calculate volume percent composition of each of the three (3) fractions

Vol % 1st fraction = Vol 1st fraction / Total Vol Rcvd x 100

Vol % 2nd fraction = Vol 2nd fraction / Total Vol Rcvd x 100

Vol % 3rd fraction = Vol 3rd fraction / Total Vol Rcvd x 100


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6. Compute Masses of Ethyl & Butyl Acetate

Combine Fractions 1 & 2 and assume it is Ethyl Acetate

Assume Fraction 3 is Butyl Acetate

Compute the Mass of Ethyl Acetate and Butyl Acetate from the Volumes and Densities of the two new fractions

7. Compute the Moles of compound in each fraction

8. Compute the Total Moles in the two fractions


molegramsgrams

WgtMol

Mass Moles

Volumex Density Mass Volume

Mass Density

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Results (Con’t)

9. Compute the Mole Fraction of each fraction

10.Compute the Mole % of each fraction


100 x N %N Percentage Mole

100 x N %N Percentage Mole

1 N N

B Moles A Moles

B Moles N Fraction Mole

B Moles A Moles

AMolesN Fraction Mole

BB

AA

BA

B

A

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Example calculations Mixture Example (1000 mL – 60% / 40% by Volume)

Ethyl Acetate (600 mL) Den – 0.895 g/mL

Mol Wgt – 88.11 g/mole

Butyl Acetate (400 mL) Den – 0.882 g/mL

Mol Wgt – 116.16 g/mole Compute moles from volume, density, molecular weight

Mole Fraction

Ethyl Acetate 6.095 / 9.132 = 0.667 x 100 = 66.7%

Butyl Acetate 3.037 / 9.132 = 0.333 x 100 = 33.3%


600 mL×0.895 g/ mLEthyl Acetate = 6.095 moles

88.11 g/ mole

400 mL×0.882 g/ mLButyl Acetate = 3.037 moles

116.16 g/ mole

Total Moles = 9.132

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Mole Percent of Distillates by Gas Chromatography Refer to Website notes on the Gas

Chromatography of Acetates Experiment Refer to Gas Chromatogram of the Equimolar

Mixture Use the TRx/Tri thermal response correction

factor for the Ethyl Acetate & Butyl Acetate peaks to adjust the distillate fraction peak areas

Obtain a Gas Chromatogram of the Standard Mixture (“A” or “B”), whichever you used in the Simple & Fractional Distillation experiment

Obtain Gas Chromatograms of each of the 3 vials you collected from the Simple Distillation and each of the 3 vials collected from the Fractional Distillation


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Mole Percent of Distillates by Gas Chromatography (con’t)

Compute the Peak Areas using Triangulation method

Note: There are two peaks on each Chromatogram

Adjust the peak areas for non-linear thermal response

• NOTE: Use TRs/Tri correction factor from the equimolar mixture used in the GC Acetates experiment

• Compute adjusted areas by multiplying measured areas from distillate fraction chromatograms the by the equimolar mixture TRs/Tri correction factor

Compute total area for peaks on each chromatogram

Compute the Mole Fraction

Compute Mole Percent


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Mole Percent by Refractive Index

Note: Add to Experiment only if directed by Instructor

Obtain temperature corrected Refractive Index values for the Unknown mixture (A or B) and the 6 simple & fractional distillation vialsUse MS Excel to create a standard regression curve from the known Refractive Index (y-axis) and Mole % Ethyl Acetate (x-axis) values in the table below


Solutions of Known Mole %and RefractiveIndex

Mole%Ethyl

Acetate

Mole %Butyl

Acetate

Measured

R.I.

Temperature(oC)

Corrected

R.I.

Ref (20oC

100 0 1.3714 21.7 1.3722 1.3723

60 40 1.3813 21.7 1.3821

50 50 1.3839 21.7 1.3848

40 60 1.3856 21.7 1.3864

0 100 1.3932 21.7 1.3941 1.3941

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Mole % by Refractive Index (con’t)

Open MS Excel

From previous slide enter “Mole % Ethyl Acetate” values into column A of spread sheet

Enter “Corrected Ref. Index” values into column B

Select data in columns “A” & “B”

Select “Format Cells” from Task Bar

Select “Number” and “4” decimal places

Select “Insert” from Task Bar

Select “Scatter Plot” (2 clicks) to plot the data


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Add a trend (regression) line and regression equation to the plot

Click on a data point in the plot

Select “Add a Trend Line”

Select

“Linear”

“Display Equation on Chart”

“Display R-Square value on Chart”

Select and move Regression Equation to upper left corner


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Select “Axis Titles”

Select “Horizontal Axis Title”

Select “Title Below Axis”

Enter text - “Mole % Ethyl Acetate”

Select “Chart Title”

Select “Above Chart”

Enter text - “Refractive Index(corr) vs. Mole % Ethyl Acetate”

Select and move chart labels as appropriate


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Mole % by Refractive Index


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Mole % Analysis by Refractive Index (con’t)

The Mole % values of the unknown mixtures are determined either:

Directly from the Regression Curve by selecting the mole % value relative to its equivalent Refractive Index value

Computed from the regression equation

Rearrange the equation as follows to compute your Mole % values

y = - 0.00022 x + 1.3949

x (Mole %) = (1.3949 – y (Measured R.I.) / 0.00022

Ex. Measured R.I. 1.3850

X = (1.3949 - 1.3850) / 0.00022

X = 45% Ethyl Acetate (55% Butyl Acetate)


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The Report (Combined with GC Distillates Report) Scan Chromatograms and insert files into report Only one (1) procedure is required for the

Distillation – Equipment setup, simple distillation, fractional distillation. Use one table to report results

The Description for each procedure involving a computation must include the computational logic behind the equation used and the equation setup with suitable definition of the variables

The “Summary” section restates the results in paragraph form

Report Preparation

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The Report (Con’t) Each procedure that produces data includes

both Simple Distillation results and Fractional Distillation results

For comparison purposes each “Simple” result should be paired with its equivalent “Fractional” result

For example: The total volume recovered for the Simple Distillation was 17.6 ml (88.0%), while the total volume recovered from the Fractional Distillation was 18.3 mL (91.5%)

Create separate procedures for the computation of mass, moles, mole fraction, mole %

Report Preparation

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Analysis & Conclusion Section Discuss the effectiveness of component

separation by Simple & Fractional Distillation based on: Analysis of the bar chart of the incremental &

fractional volumes, including the significance of the amounts in the 2nd fraction (95oC – 105oC)

Mole % values from the computed mass (from volume and density) of the fractional volumes

Mole % from peak areas obtained from Gas Chromatography Compare the results for the original

undistilled A or B mixture and the distillate fractions

Mole % from Refractive Index

Report Preparation

1/17/2015 1 experiment – simple & fractional distillation evaluation of the relative...

Documents

vapor pressure vapor

atmospheric pressure

liquid increases

atmospheric boiling

temperature boiling

applied pressure

confined liquid

normal boiling point