What�s Cookin�� LAB 1�� Fall 2005

Ethanol:� Food & Energy & Drug

Purpose

�� 1)� To acquaint you with some of the glassware and techniques routinely utilized in the isolation of natural products.

�� 2)� To prepare, purify and investigate some properties of ethyl alcohol (ethanol).

�� 3)� To become familiar with a Refractometer and use it to obtain the Index of �� Refraction of your ethanol.

Introduction

�� In this lab we will generate ethanol.� Ethanol has many uses and its structure is shown in Figure 1.� It belongs to a to a class of organic molecules known as alcohols.� In fact, this is so common of an alcohol that people often use the word alcohol when referring to ethyl alcohol, which is ethanol.� Ethanol is the active component in beer, wine and booze.� Recently it has been used as a fuel additive, this solution is known as gasohol, and is common at many gas stations.� Another use for ethanol is in the preparation of tinctures.� Ethanol is often used to extract the desirable active components of a plant, drank to feel good and used as a fuel.�

Figure 1:� Four different, yet common ways to represent ethanol.

�� The unique way in which we prepare this solution warrants a few words.� We will use yeast to synthesize the ethanol.� This process, known as fermentation has a long herstory.� Coupling chemistry with a bit of some biology, the enzymes found in yeast can generate ethanol from sugar molecules.� Thank you yeast?�

�� The initial mixture we generate will consist of an ethanol/water solution along with a lot of gnarly solid material, which we do not want.� Our initial purification will be to filter off the unwanted solids leaving mainly the ethanol/water solution.� The simplest solutions have two components.� The major component is the solvent and the minor component is the solute.� Solutions can be made from liquids, solids and gases, in any combination and are explained in other places.� In our solution both the solute (ethanol) and solvent (water) are liquids at room temperature.

�� The ratio of solute to solvent can be expressed in a number of different ways and is known as concentration.� Molarity, molality, normality, g/ 100 mL, mass %, volume % are but a few of the ways to express the ratio of a solute to solvent.� Our initial solution, prior to distillation will be mainly water.� This then will be distilled to yield a solution, which is mainly ethanol.� 95% ethanol is as pure as we can get via distillation.� Azeotrope is when

�� Once we obtain our ethanol we will burn it.� Upon combustion with air, ethanol produces carbon dioxide, water and heat.� In the body alcohol can also be used as a fuel source and can be incorporated into fats.�

�� We will utilize three techniques today and they are described below.

�� Gravity Filtration allows one to remove solids from liquids in a mixture.� It is a quick and easy method.� Note the set-up and make a sketch.� The things you need to pay attention to is the type of filter paper to be used.� Some allow for rapid filtration depending on the pore size of the filter paper.� Since there are many manufactures of filter paper there are many different systems.� One can and often does just use a chemwipe^TM or piece of cotton/glasswool.� This is but one type of filtration.

�� Distillation is a common method for purifying volatile organic molecules.� The solution in question is heated to its boiling point, there by creating a gas (vapor).� This vapor will then rise and come into contact with a water-cooled condenser, which cools the vapors.� This slows down the molecules, which condenses the vapor back into a liquid phase.� The condensed liquid does not return back into the reaction vessel but it is directed into a separate receiving flask.� This is possible by properly assembling your glassware.� You will need to sketch such a system and I will have one set up for guidance.� This is but one type of distillation.

�� Refractive index is the ratio of the speed of light through your material as compared to the speed at which light travels in a vacuum.� The light usually corresponds to that of the D line of sodium.� Refractive indexes can be used to judge the purity of a sample.� Refractive indexes have been measured for a good many chemical compounds.� Hence, if you believe you have a particular liquid or oil (based on boiling point and/or some other piece of evidence) you usually will be able to measure its refractive index and compare it to a known authentic sample.� Knowing the refractive index of a mixture one can estimate of the % composition of each component in the mixture.� Imagine we had mixture of two liquids, liquid A had a refractive index of 2.0 and liquid B had a refractive index of 1.0.� If the refractive index of the mixture was 1.5, the solution contained a fifty/fifty mixture of each.�

LAB IS A PARTICIPATION ACTIVITY SO PARTICIPATE & HAVE FUN

Procedures

Day I:

�� Into a 250 mL Erlenmeyer flask is combined 24 grams � 1 grams of molasses and 100 mL of water, taking care not to make a mess.� Mix the contents by swirling until the molasses is dissolved.� Set this aside for the moment.� In a clean 50 or 100 mL beaker place a small amount of brewers yeast (� 6 grams) and 20 mL of water.� Mix these together until you obtain a thin paste.� Carefully warm the yeast mixture over a low flame until the paste reaches a temperature of 39˚ C.� Do not overheat this paste!� After warming to the appropriate temperature, transfer this paste into your 250 mL Erlenmeyer containing the dissolved sugars.� Mix well so all components make intimate contact with each other, taking care not to make a mess.� At this point you are ready to assemble your fermentation tank.� Note Figure 1 for guidance.� The solution of calcium hydroxide (commonly called limewater) helps remove the carbon dioxide (CO₂) from solution, which enhances the formation of ethanol.� After all is properly assembled, label the fermentation tank with your mark and set it out of harms way until Saturday.�

Day II

�� It is now Saturday.� Retrieve your fermentation tank, taking care as not to disturb the material at the bottom of the Erlenmeyer.� Obtain the necessary apparatus to perform a distillation.� Use the demo for guidance.� Into a 500 mL round bottom flask, decant your newly formed ethanol solution.� You may want to use a funnel/filter to help assist in the transfer.� Leave behind as much of the solid yeast type gunk that sits at the bottom of the flask.� After the transfer is complete, assemble your distillation apparatus.�� Allow Gary/me/neighbor to check it prior to starting your distillation.� They will be paying attention to thermometer height, hose connections and things like this.� Note question 8.

Get yourself a set of 5 or so clean & dry test tubes, and a rack to put them in.

�� Begin your distillation.� Collect �1.0 mL portions of distillate in test tubes and set aside.� Record the temperature at which each portion is collected.� Do this for a total of five test tubes if possible, (and at most).� The temperature of the distillate shall guide you.�

Caution:� Save some ethanol from fire!

�� The % ethanol in each tube will be determined two different ways.� The first way utilizes the fact that ethanol is flammable.� Obtain an appropriate balance and a watch glass.� Tare the watch glass on the balance, which will be �protected� from the heat.� Pour most your sample from tube # 1 onto the glass and record the mass of your solution.� Put a match to it taking care to minimize the amount of hair you burn and �please be careful�.� After burning is complete, record the new mass.� This procedure should be done in somewhat of a dark room if possible to help see the flame.� Repeat for each sample.� There may not be time for all of us to do every sample.� If this is the case obtain data on the most flammable samples; use your wits here.� Always consider time management!

Hope you saved some ethanol from fire!

�� The second method of analysis is refractive index.� I will take the time and demonstrate this instrument to you.� The Aldrich Chemical Catalog is a good reference source for known refractive index values.� After you get proficient with the refractometer, make at least two independent measurements.� These samples should coincide with the burned samples.� Record this data.

observations & calculations

Post Lab and Write-Up

�� Write a short paragraph summarizing your experience with this lab.� Include any unusual observations and comments on the likes and dislikes of the lab as well as thoughts on how to improve this for future students.� Answer the questions and complete the table on the next page.� One question deals with the concept of LD₅₀ values.� Please make sure you understand this concept.� Pay attention to units.

Questions

1.� What is the refractive index of pure ethanol and from what source did you get this?

2.� What was the refractive index of two samples of the ethanol you isolated?

3.� Ethanol is soluble in water.� What does this mean?� Draw the structure of both ethanol and water and show, on a molecular level why they are soluble in each other.�

4.� Complete the last sentence on page one of this lab.

5.� Please note the edition of the Merck Index utilized in Lab.

6.� Three common types of solutions sold as drinkable liquids are beer, wine and hard liquor.� What proof are each of these and what % ethanol is in each of these?

7.� What is the LD₅₀ of ethanol and what mass of ethanol would it take for you to reach your LD₅₀ value?

8.� Sketch the distillation apparatus you utilized in this lab.� Note the water hoses and how water always goes in at the bottom and out at the top.�

Data and Calculations

Sample #	Temp. range	mass initial	mass final	% ethanol	proof	Refractive�� index
1
2
3
4
5
6