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T H E C H E M I C A L E D U C A T O R h t t p : / / j o u r n a l s . s p r i n g e r - n y . c o m / c h e d r
c 1 9 9 6 S P R I N G E R- V E R L A G N E W Y O R K , I N C . 1 0 . 1 0 0 7 / s 0 0 8 9 7 9 6 0 0 0 9 a
L a b o r a t o ri e s a n d D e m o n s t ra t i o n s
The Salting Out of Ethanol and Water:A Colorful Illustrationof IntermolecularForcesEUGENE T. SMITH
Department of Chemistry
Florida Institute of Technology
Melbourne, FL 32901-6988, USA
Water and ethanol are made immiscible by the
addition of potassium carbonate. This effect
can be visualized in a large lecture hall throughThis
demonstration
can be used to
introduce or
illustrate the
concept of
intermolecular
forces.
the initial addition of a few drops of bromoth-
ymol blue and a drop of acid to a water/ethanol solution. After
addition of potassium carbonate, the yellow solution separates
into two phases, a colorless aqueous and blue organic phase. This
demonstration can be used to introduce or illustrate the concept
of intermolecular forces.
The process of salting out , the separation of an organic phase
from an aqueous phase by the addition of a salt has been known
for nearly a century [1]. This method is commonly used by bio-
chemists in the purification of proteins [2], [3]. Weak intermolec-
ular forces (e.g., hydrogen bonds) between organic molecules or
nonelectrolytes and water are easily disrupted by the hydration
of electrolytes. Water and ethanol, which are soluble in all pro-
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T H E C H E M I C A L E D U C A T O R h t t p : / / j o u r n a l s . s p r i n g e r - n y . c o m / c h e d r
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portions (i.e., miscible), are made immiscible by the addition of potassium carbonate in
a variation of a demonstration previously described [1].
Two test tubes with stoppers, 10 ml each of ethanol and water, a few grams of potassium
carbonate, a few drops of bromothymol blue indicator, and a drop of 1 M HCl are required.
Ethanol, water, pH indicator and hydrochloric acid are combined in the first test tube to
form a single-phase yellow solution. Potassium carbonate is added to the second test
tube. The contents of the first test tube are added to the second test tube, and the mixture
is stoppered and shaken. The solution will turn blue and separate into two phases, a
colorless aqueous and blue organic phase. A number of test tubes containing the reactants
are distributed throughout a lecture hall, and the students are allowed to mix the reactants
themselves. In this manner, the students get a better view of the salting-out process. An
alternative approach is to scale up the reaction in two large graduated cylinders.
This demonstration, which takes only a few minutes to set up, can be used to illustrate
or introduce the concept of intermolecular forces, as well as to illustrate an acid/base
reaction. Some questions to be pondered by the students include the following:
1. Which phase is water, which is alcohol? Why?
2. Is the separation of water and alcohol complete?
3. Could other liquid pairs or salts be used?
4. Could a dye be found that would wind up in the water rich phase? Why?
The intermolecular forces between water and ionic compounds (e.g., ion-dipole) in the
aqueous phase, and the intermolecular forces between the organic dye and ethanol (e.g.,
dispersion) in the organic phase are discussed. It is important to note that the color change
of the pH indicator is attributed to the fact that potassium carbonate acts as a base in water,
and has nothing to do with the salting out effect. The pH indicator may also be substituted
with food coloring.
Handling andDisposal:The waste mixture from this demonstration can be safelyflushed
down the drain with water.
REFERENCES
1. Shakhashiri, B. Z. Chemical Demonstrations; University of Wisconsin Press: Madison, WI., 1983;
Vol. 3, p. 266.
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T H E C H E M I C A L E D U C A T O R h t t p : / / j o u r n a l s . s p r i n g e r - n y . c o m / c h e d r
c 1 9 9 6 S P R I N G E R - V E R L A G N E W Y O R K , I N C . S 1 4 3 0 - 4 1 7 1 ( 9 6 ) 0 1 0 0 9 - 6
2. Lehninger, A. L. Principles of Biochemistry; Worth: New York, 1982; p. 144.
3. Zubay, G. Biochemistry; Addison Wesley: Reading, MA, 1983; p. 51.
