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