Ethanol Is Again Viewed as One Part of a Solution

Experiment 5

Liquids: Distillation, Boiling Points, and the Fermentation and Distillation of Ethanol

Objectives

Distillations are performed to isolate volatile chemicals from non-volatile or less volatile chemicals. This experiment addresses how distillations (both unproblematic and fractional) can be used to isolate chemical in pure grade.  In addition, boiling points and other physical backdrop can be adamant, including refractive index and density of purified materials. Nosotros also setup a fermentation to isolate ethanol from these mixtures.

Background

Parts A and B will be performed during the first laboratory catamenia.  Part C, which is the distillation of ethanol from a fermentation mixture, will be performed during the 2d laboratory period.

Techniques and procedures that you volition perform during this experiment include:

• Elementary distillation
• Fractional distillation
• Refractive index determination

This experiment is performed in iii parts over two days.  Parts A & B are performed during the showtime day.  Role C is performed during the second 24-hour interval of lab.  The fermentation setup is done i week prior to the start of Part C.

Function A: Purify 2-propanol by simple distillation. This technique shows how to purify, by distillation, a volatile organic compound.  This procedure is good for purification of volatile compounds from compounds that are not volatile, but not very successful for mixtures of compounds, each of which is volatile.  Part B describes how to fractionate these types of mixtures using partial distillation.

Part B: Separate ethanol from h2o by fractional distillation.  Compounds which are volatile will each distill at temperatures well beneath their actual boiling points (e.m., call up the vapor force per unit area of h2o?).  Nosotros need to have a process that allows for more efficient separation of these volatile liquids, and this is the process of fractional distillation.

Part C: We will prepare a fermentation of glucose to produce ethanol.  The ethanol from this fermentation will be isolated by partial distillation (using the procedure described in Office B).  You must repeat your fractional distillation, in club to remove h2o, which, unfortunately predominates during the first partial distillation.  Once you have repeated your fractional distillation, you can decide the amount of booze in your concluding distillate sample.

In many of the previous experiments that we take performed, (east.g., the experiments involving extraction, separation, Re-crystallization, and chromatography), you take learned that a chemist must be able to exploit the specific physical properties of the components of a mixture in society to efficiently separate and purify the desired chemical compound. The most common method for separating and purifying volatile liquids is distillation, which makes apply of the specific boiling points of the liquid components in the mixture.

When there is only ane volatile liquid, or when ane of the liquids has a boiling betoken well below the others, a simple distillation can be used. However, if there are two or more than liquid components, which accept boiling points near each other, a fractional distillation must exist used (the theory of distillations is discussed in Chapter 35 of Zubrick).

In Part A of this experiment you will comport out a simple distillation of 2-propanol (isopropyl alcohol), which has been contaminated with a not-volatile impurity (a dye). In Part B, you will conduct out a fractional distillation of a 50:50 (five/v) mixture of ethanol and water.

During each of these experiments, you will make up one's mind the boiling bespeak of the volatile organic compound during distillation. You volition monitor the temperature that the volatile liquid has, in the gas stage using a thermometer.  This temperature should remain abiding, and should reflect the actual boiling indicate of the chemical under the atmospheric conditions of the day. Report this boiling point as part of your data.

Process

Part A: Simple Distillation of 2-propanol

Safety:two-propanol is a highly flammable liquid and a severe middle irritant -- no flames will be allowed in lab while information technology is in use. As for every experiment, goggles must exist worn, even though you lot may not actually be  working the chemicals, if there is anyone using 2-propanol in the lab.

Follow the instructions in capacity 19 and twenty of Zubrick for setting up a uncomplicated distillation apparatus, although the instructor will go through the setup, and the use of your organic kit.  You will apply a 50-mL circular bottom flask as the distillation pot, and a 100-mL round bottom flask every bit the receiver.  As a standard rule, anytime you lot are boiling an organic compound, you volition always include a few (not a handful!) boiling stones to keep the solution humid smoothly!

Using a beaker (not a graduated cylinder) obtain well-nigh 30-forty mL of "impure" 2-propanol (this sample of 2-propanol has had a modest amount of a soluble, not-volatile dye added to information technology every bit an impurity). Add the two-propanol to the distillation pot (never pour anything through a ground-glass opening without using a funnel), add the boiling stones, and brainstorm the distillation (remember to turn on the cooling h2o earlier you plow on the heat). Collect your distillate in a pre-weighed graduated cyclinder (x-mL or 25-mL or 50-mL cylinder).

Once the temperature starts to rise above room temperature, you should first to record the thermometer reading every minute.

You should commencement to record the temperature at whatsoever time up to when the solution starts to boil. Record every minute the temperature you read. Continue to practise your distillation until you have nerveless about 20 mL of distillate. Be sure that the distillation pot never goes dry (never let a heated flask go dry!).

Yous must plot your information by hand using graph paper, or you tin use Excel or another graphing program for a graph for inclusion in your lab notebook and written report.

Measure the book of the distillate nerveless.  Using a pre-weighed graduated cylinder (10-mL or 25-mL or l-mL cylinder), you should decide the density of the collected distillate. You volition likewise determine the refractive index of your distilled liquid.  Your instructor volition describe how a refractive index is determined.

Dispose of your liquid, and whatever liquid remaining in the distillation pot, in the liquid waster.  Be sure to make certain that no boiling stones are deposited into the liquid waste material.  Put the boiling stones in the solid waste container.

Office B: Fractional Distillation of an Ethanol/Water Mixture

Safety: Ethanol is a flammable liquid and an irritant; avert contact and inhalation -- wear gloves while handling it. No flames will be allowed in lab while ethanol is in utilise.  Goggles must be worn whenever anyone is using chemicals.

Ready a partial distillation apparatus equally demonstrated by your instructor.  Use drinking glass beads to pack the fractionating cavalcade (your instructor will demonstrate how to pack the cavalcade). Try adding some drinking glass beads directly to your fractionating cavalcade. If the glass beads stay in the cavalcade, there is no problem, simply if any chaplet go through, effort calculation a larger amount of glass bead, and their packing within the fractionating cavalcade should allow them to stay in place. Do not ever use glass wool or annihilation besides beads in the fractionating columns.

To do this part of the experiment, you will use a 100-mL circular bottom flask as the distillation pot. You will demand a number of receivers; it is all-time to utilise test tubes. Mensurate into ane examination tube almost 4 mL of h2o. Employ this sample to know how much liquid you lot demand to obtain almost four mL of distillate during this part of the experiment. Continue collecting 4-mL samples until y'all have collected well-nigh 30 mL of distillate. Make up one's mind the refractive index of each collected sample, as well as determining the refractive alphabetize for pure ethanol and pure water.

• Obtain virtually l.0 mL of the fifty% (five/five) ethanol/h2o mixture, and pour into the distillation pot.
• Add a few boiling stones.
• Plough on the heating mantel to obtain a steady boiling mixture.
• Monitor time and temperature during the entire distillation process

Starting time recording the temperature as before long as your sample begins to eddy. Record the temperature every 30 sec. Collect your distillate into examination tubes. Y'all should collect most 4 mL in each exam tube, just it is not necessary to measure each tube. Equally a comparison, add together about four mL of h2o into a test tube. Collect almost the same amount of liquid into each of the tubes during the distillation procedure. Continue recording the temperature until you stop collecting your samples. Collect about 30 mL of distillate.

You must plot your information past hand using graph paper, or you lot can apply ChemWorks™ on the computers for inclusion in your lab notebook and written report. You should accept two plateaus, i for the boiling point of the ethanol and the other for the boiling point of the water. Your graph for your lab written report and for your notebook must evidence these two plateaus.

After the distillation has finished, you lot volition take a good determination for the boiling signal of ethanol.  Determine the refractive index for each of your samples.

Do not ever throw any glass beads abroad.  At an expense of about 25 cents ($0.25) per drinking glass bead, they are very expensive.  Keep your glass beads in your fractionating column (add together some tissue to the pinnacle to prevent spillage) until the next lab period. Never throw abroad any glass beads.

Part C: Fermentation and Distillation of Ethanol

Yeast ferment sugars to produce ethanol. You will use glucose (dextrose) as the sugar the yeast will apply for alcohol production. Glucose has a tooth mass of 180 one thousand/mol. The molar mass of ethanol is 46 grand/mol. The other product of fermentation is carbon dioxide, which we will not consider in the current experiment. The equation for this reaction is as follows:

Based on the balanced equation, one (1) mole of glucose will yield 2 (ii) moles of ethanol. Based on these molar ratios, one mole of glucose is 180 thou, and two moles of ethanol is 92 grams. On the other manus, 1 mole of sucrose will yield four moles of ethanol. Your Teacher will inform you which carbohydrate you will exist using.

• How many grams of booze would you produce, if you started with 60.00 grams of glucose (MW=180.0)?
• If you started with 60 grams of sucrose (MW=342.3), how many grams of ethanol would you produce?

Based on the amount of carbohydrate (glucose or sucrose) yous actually started with (based on the amount you weighed out), what is the theoretical yield of alcohol that you should produce? Apply this value to decide your percentage yield after you have finished this part of the experiment.

Grams of glucose (or sucrose) fermented: _________________ grand

Theoretical yield of ethanol: __________________ g

Fermentation Setup

Set the fermentation container in the following manner:

• Identify 60.00 chiliad (0.33 mole) of glucose (or of sucrose) into a 250-mL Erlenmeyer flask (or the "beer-canteen fermented")
• Add 175 mL of distilled h2o
• Add 20 mL of the Pasteur's salts solution (see Footnote 1 for formulation)
• Add two.00 thousand dry yeast, that has been rubbed to a thin paste (to break up yeast clumps) with about 10 mL of DI water
• Shake vigorously to mix the contents of the fermentation container (containing all reagents)
• Close the container with a rubber stopper fastened to a piece of glass tubing continued by a piece of latex tubing. The drinking glass tubing at the terminate of the latex tubing volition be inserted into a tube containing water (two-three mL DI h2o) and a small amount of mineral oil (cascade a petty mineral oil to comprehend the water in the test tube) to forbid evaporation.

Allow the fermentation mixture to stand up at a temperature of 25-35^oC until fermentation is complete (near a calendar week is required).

First Distillation of Fermentation Mixture

After the fermentation is consummate, you will distill the booze from the liquid mixture, including the solid, particulate material that is non soluble. Gently pour all of the liquid into a 500-mL round-bottomed flask (checked out from the stockroom).  The liquid will be somewhat cloudy, but this volition not interfere with the first distillation (exercise not ever permit a distillation flask become dry, but this should be of little concern here since we volition only collect a fraction of the liquid via distillation).

Add a few (6-viii) humid stones to the flask.  Attach a fractional distillation cavalcade (filled with drinking glass chaplet, as described in Role B) to the elevation of the distillation flask, and attach the however head and condenser unit of measurement. Y'all do non need to monitor the temperature equally the commencement distillate is mostly water, and then the temperature will be about 100^oC.  Collect virtually 50 mL of distillate into a pre-weighed graduated cylinder (a 50- or 100-mL graduated cylinder tin can be used).

Later the get-go distillate has been collected, observe and record the collected book, and weigh the graduated cylinder to determine the mass of nerveless distillate (full mass of cylinder containing the distillate minus the mass of the empty graduated cylinder).  Yous should now calculate the density of the distillate, based on the mass of the distillate you only adamant divided by the volume nerveless.  From the Table of Densities of aqueous ethanol solutions, given in Footnote 2, calculate the mass of booze collected in this first distillate.

To make your determination of the amount of ethanol isolated, you can estimate your percent booze using the table at the end of this experiment. This table shows you several means to determin the amount of ethanol in your sample based on density. The easiest column to use is the first column which shows the mass percent of booze (% past mass) as follows:

Using the density of your distillate from the above calculations, make up one's mind the percentage booze ( you may have to extrapolate (e.g., Calculate the percent yield of ethanol produced in the fermentation, based on the theoretical amount of ethanol that would exist produced from the starting amount of glucose (each glucose molecule produces two ethanol molecules).  This "crude" distillate will be used in a second fractional distillation.

An additional tabular array is available, using an interpolative procedure to determin percentages which do not fall within the larger per centum range shown in the table below (percentages are in 5% increments). The new table (which is an Adobe pdf document) shows y'all how to get to the percent values, based on density, in unit values, e.g., 45%, or 46%, or 47%, etc. The highlighted values in this pdf document shown how to determine percentage concentration values betwixt 45% and 50% ethanol. You lot can download and print this certificate at this URL of a pdf document.

Discard the remainder left in the distillation pot, which contains more often than not water.

One can obtain 95% ethanol (but not 100% ethanol; practice yous know why? What is an azeotrope?) from the dilute alcohol mixture obtained during the get-go distillation.  For the second distillation, monitor the boiling indicate advisedly, as you lot should collect the fabric that distills at a temperature of 78-82^oC; if likewise trivial distillate is obtained in this range, go on the distillation and collect the fraction boiling at 82-88^oC.

Prior to doing your second distillation, empty the drinking glass beads from the fractioning cavalcade into a beaker y'all will wash them yourself with soap and water, and then reuse them. Also, you need to wash with soap and h2o each of the post-obit pieces of glassware:

• Fractionating column
• Withal caput
• Condenser column

You can at present re-assemble your distillation setup for a fractional distillation, and and then follow the procedure for collecting and analyzing your second-distillate liquid. At the end of the experiment, put the used glass chaplet into a beaker on the Instructor'south demote to exist washed by the Stockroom Personnel. Practise non throw the glass bead away.

Procedure for collection of ethanol via a second distillation:

1. Add together the booze-water mixture from the first distillation (afterwards weighing and determining its density) to a 100-mL round bottom flask.
2. Add a few humid stones to your circular-lesser flask (distillation pot) to maintain a tiresome, steady boiling.
3. Showtime monitoring the temperature every bit soon equally you turn on the rut, or at least prior to the solution boils. Monitor the temperature at regular intervals, usually every infinitesimal, until you stop collecting your samples.
4. Starting time to collect 4-mL samples (using yous conical vial in the organic kits or a exam tube) until the temperature rises significantly above the normal 78-82^oC temperature, as described higher up. It is still permissible to collect above the 82^oC caste range, but your samples comprise more and more than water. However, if you lot have not collected at least 4-5 samples, each of virtually 4-5 mL volumes, continue to collect samples (regardless of temperature) until at least 20 mL of solution is nerveless. Based on theoretical yeields, and actual lab experience, y'all could accept produced 30-36 mL of ethanol during your fermentation, so collectin at least 20 mL is not out of reason.
5. Practise non determine a refractive, but yous must determine a density for each sample. To do this, collect about four-5 mL in a conical vial (as mentioned above), and and so immediate transfer the contents of the vial into a pre-weighed 10-mL graduated cylinder. After transfer of nerveless cloth into the x-mL graduated cylinder, reattach the vial to the vacuum adapter, and collect another four-5 mL sample.
6. Determine the mass and book of the sample in the 10-mL cylinder to calculate a density of the sample. After determining the mass and volume, transfer its contents into a pre-weighed 50-mL graduate cylinder to collect all samples for an overall density and yield of ethanol for the entire experiment.
7. Later you take analyzed individually the 4-mL samples, combine your 4-5-mL nerveless distillate samples into the 50-mL graduated cylinder, the total book, the mass of the sample in the 50-mL cylinder, you tin determine the density.
8. From the density only determined (step #7), determine the total mass of ethanol collected during the second fractional distillation. No need to determine a refractive index every bit density (and full mass of solution) will be our criterian for yield.
9. Determine pct yield based on the overall yield from step #8, by dividing the actual yield by the theoretical yield times 100 to get a per centum yield.

Based on the amount of collected alcohol, its density, what is the pct yield? What is the theoretical yield?. Your instructor volition help you make up one's mind the percentage of booze based on your refractive index and density determinations.

Do not throw any glass beads away.  At an expense of nigh 25 cents ($0.25) per glass dewdrop, they are very expensive.  After all distillations are completed, pour your glass beads into a large chalice on your instructors bench, and so they can be cleaned.  Never throw drinking glass beads away.

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Chemicals and Reagents

Compound	MW	Amount	mmol	mp	bp	Density	η D	msds
2-propanol (isopropyl alcohol)	60.i	50 mL		-88.5	82.5	0.78505	i.3772	msds
Dextrose (glucose)	180.16	50.0 g	277.53	146	---	i.54		msds
Sucrose	342.three	50.0 g	146.07	160-186	---	ane.59		msds
Ethanol	46.0414			-114.1	78.5	0.viii	1.3614	msds
Compound	g/mol	grams or mL	10-3 Yard	oC	oC	grand/mL	ηD	msds

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Source: http://home.miracosta.edu/dlr/210exp5.htm

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