LAB 9. ESTERS, FATS, AND SOAP:
ESTERIFICATION & SAPONIFICATION
PURPOSE: To synthesize esters from carboxylic acids and alcohols.
To synthesize soap from fat and lye.
To observe the physical and chemical properties of esters and soap.
SAFETY CONCERNS:
Always wear safety goggles.
Sulfuric Acid, Hydrochloric Acid, and Glacial Acetic Acids are dangerous to skin eyes, mucus
membranes and clothes. Sodium Hydroxide is caustic to skin and will dissolve eyes.
Use these with caution. Wash with soap and copious amounts of water if contacted.
ESTERS:
When carboxylic acids are combined with alcohols in the presence of an acid catalyst they react
to form esters and water. The name of an ester indicates the acid and the alcohol that combined
to form it. The first word in the name comes from the alkyl group of the alcohol, and the second
word is the name of the acid with its –ic ending changed to –ate.
Carboxylic Acid
H H O
H C C C O H +
H H
propanoic acid
Ester
Alcohol
H H
H O C C H
H H
ethyl alcohol
ethanol
H+
H H O
Water
H H
H C C C O C C H + H O H
H H
H H
ethyl propanoate
water
Many esters are colorless liquids with pleasant, fruity aromas. The aroma and flavor of many
foods are due to the presence of esters.
FATTY ACIDS AND FATS:
Fats and oils are mixtures of complex esters. Fat esters are made from long chain carboxylic
acids (called fatty acids) and an alcohol containing three OH groups (called glycerol).
A common fat is called a triacylglycerol or triglyceride. The hydrocarbon chain of the fatty
acids determines the physical and chemical properties of the compound. Triacylglycerols made
from long-chain (C-16 to C-18) saturated fatty acids (like palmitic and stearic acids) are solid or
semisolid at room temperature. Solid animal fats contain an abundance of long saturated fatty
acids.
Triacylglycerols made from long-chain unsaturated fatty acids (like oleic or linoleic acids) are
liquid oils at room temperature. Liquid vegetable oils contain an abundance of long unsaturated
fatty acids.
A few oils owe their characteristic liquid nature to the presence of shorter chain fatty acids (C-6
to C-14). Coconut oil contains large amounts of lauric (C-12) and myristic (C-14) acids, as well
as smaller amounts of C-6, C-8, and C-10 acids.
CH110 Lab 9. Esters, Fats, and Soap (W14)
101
Common Fatty Acids
Saturated
O
C
12
O
C
14
OH
Lauric Acid
OH
Myristic Acid
OH
Palmitic Acid
OH
Stearic Acid
O
C
16
O
C
18
Unsaturated
O
9
C
16
O
9
C
18
OH
Palmitoleic Acid
OH
Oleic Acid
OH
Linoleic Acid
O
12
9
C
18
Synthesis of a Typical Triacylglycerol:
O
H
HO
H C OH
C
O
H C OH
+
H C OH
HO
C
O
H
HO
Glycerol
1,2,3-propantriol
C
Stearic Acids
H+
O
H
O
C
H C
O
H C
O C
H C
O
H
O
+ 3H2O
C
Glyceryl Tristearate (Tristearin): a typical triacylglycerol
102
CH110 Lab 9. Esters, Fats, and Soap (W14)
SOAP:
Hydrolysis of an ester is the reverse of the synthesis of an ester. Hydrolysis of a triacylglycerol
into glycerol and fatty acids can be catalyzed by either strong acid or strong base.
The general process of hydrolyzing esters with caustic alkali’s (strong bases such as sodium
hydroxide, NaOH or potassium hydroxides, KOH) is called saponification. The products of
basic hydrolysis of fats or oils are glycerol and the salts of fatty acids called soaps.
The term saponification comes from the ancient art of soap-making, performed by heating fats
and oils with potash (potassium hydroxide) or lye (sodium hydroxide) solution obtained from
leaching wood ashes with slaked lime.
O
H
O
H C
O
H C
O C
H C
O
H
Glyceryl Tristearate (A Fat)
C
O
C
NaOH, H2O
O
H
Na O
H C OH
Sodium Stearates (A Soap)
C
O
H C OH
+
H C OH
Na O
C
O
H
Glycerol
1,2,3-propantriol
Na O
C
Polar hydrophilic end
attracts water
Nonpolar lipophilic end
attracts grease
Soap owes its cleaning ability to the formation of micelles which can encapsulate grease or oil
and make it water soluble. Micelles are destroyed by “hard” water ions such as Ca2+ and Mg2+.
These ions precipitate the fatty acid anions causing a “scum” to form. In recent years, synthetic
detergents (called “syndets”) have been developed which are less affected by hard water ions
since the magnesium and calcium salts are quite a bit more soluble.
A Micelle
O C
O
C
O
O
O
C O
O
C
O
O
C O
O C
O
O
O
Na O
A Detergent
S
O
C
O
CH110 Lab 9. Esters, Fats, and Soap (W14)
103
PROCEDURES:
ACTIONS:
NOTES:
I. PREPARATION OF ESTERS:
1. Set up a hot water bath by filling your largest beaker 1/3 full of
water and heating it on a hot plate only until it reaches 85oC. 1
2. On Obtain 4 stoppered test tubes and label them A, B. C. and D.
with a pencil2 or grease marker.
3. Into tube #A put
20 drops ethanol (CH3CH2OH)
20 drops glacial acetic acid (CH3COOH) and
10 drops concentrated sulfuric acid (H2SO4) 3
Into tube #B put
A match head sized scoop of Salicylic acid
20 drops methanol (CH3OH)
5 drops concentrated sulfuric acid (H2SO4)
Into tube #C put
20 drops pentanol4 (CH3CH2CH2CH2CH2OH)
20 drops glacial acetic acid (CH3COOH) and
5 drops concentrated sulfuric acid (H2SO4)
Into tube #D put
A match head sized scoop of Benzoic acid
20 drops ethanol (CH3CH2OH)
10 drops concentrated sulfuric acid (H2SO4)
4. Stopper and shake each tube to mix well.
5. With the stoppers on loosely, place all 4 tubes into the 85oC
water bath for 10 minutes.5 Continue working on other parts of
the lab and come back later to check the tubes.
6. After 10 minutes remove the stoppers from each tube and note
the odor produced.6
104
CH110 Lab 9. Esters, Fats, and Soap (W14)
1
Use your thermometer
to
monitor
the
temperature.
Do not
overheat.
2
Some test tubes have a
white patch on which
you can write with
pencil.
3
Concentrated Sulfuric
Acid
(H2SO4)
is
dangerous to your skin,
eyes, and clothes. Do
not breathe the vapors.
Wash hands with soap
and water immediately
if contacted.
4
Pentanol is also known
by its common names:
pentyl alcohol and amyl
alcohol.
5
You do not want the
water to get too hot or
the esters you make will
evaporate away.
6
You should be able to
detect the aroma of
banana, butter rum,
fingernail
polish
remover and the mint
scent of wintergreen.
Decide which of the
tubes belongs to which
aroma and record the
correct aroma on the
report sheet.
II. SOAP:
7
A. Preparation:
1. Into a porcelin evaporating dish pour
2 mLs vegetable oil7
3 mLs ethanol8
20 drops 50% Sodium hydroxide (NaOH) 9
Stir with a stirring rod to mix well.
2. Heat the mixture gently over medium heat on a hot plate or
the moderate flame of a laboratory burner. Stir constantly
until it becomes a thick paste.10
3. Allow the dish to cool and record your observations on the
report sheet.
4. Place the soap you just prepared into a 150 mL beaker with
about 50 mLs of deionized water. Heat the mixture, with
stirring, until all of the solid soap has dissolved in the
water. 11
5. Test the pH of this soap solution and record the result.12
Use this soap solution in each of the following procedures.
B. Purification:
1. Obtain two 50 mL beakers. Into beaker #1 pour 10 mLs of
the soap solution you just made and allow it to cool.
2. Into beaker, #2, pour 10 mLs of a detergent solution.
3. To each beaker add solid sodium chloride (NaCl) a little at
a time with stirring, until no more NaCl dissolves and the
bottom of the beaker is covered with NaCl. Record your
observations on the report sheet13.
4. Remove the mass of pure soap floating on the surface of
beaker #1. This could be done by scraping it off the top
with a spatula or piece of filter paper.
5. Put a small piece of the purified soap into a test tube and
dissolve it in deionized water. Stopper the tube and shake
the soap to see if it lathers.14
6. Test the pH of the purified soap solution in the test tube and
also test the pH of the detergent solution in the second
beaker. Record the results.
CH110 Lab 9. Esters, Fats, and Soap (W14)
Vegetable oils, or solid animal
fat would work as they are all
triacylglycerols.
8
Ethanol is a good solvent to
dissolve both the nonpolar oil
and the polar NaOH in order to
better mix them together.
9
Sodium Hydroxide (50%
NaOH)
is
extremely
dangerous. Make certain you
are wearing eye protection.
Do your best to avoid splashes.
If skin contact is made wash
immediately with soap and lots
of water.
10
Do not overheat and burn
your soap.
11
If there are clumps that will
not dissolve, scoop them out
and discard them.
12
This soap solution contains
some
leftover
sodium
hydroxide that didn’t react so it
will show a very basic pH.
The crude basic soap is too
harsh to use on your skin so it
must be purified.
13
Soap can be forced out of
solution by dissolving NaCl in
it. Water can only dissolve a
limited amount of stuff and
since NaCl is more polar than
the long hydrocarbon chain of
the soap, the water lets go of
the soap and dissolves the
NaCl. The soap that has been
let go floats to the surface of
the water. The NaOH leftover
from the preparation of soap
reaction is very polar like
sodium chloride so stays
dissolved in the water.
Therefore, the soap that comes
to the surface of the water is
now more pure.
14
You could also test the
lathering ability by using the
purified soap to wash your
hands.
105
C. Reactivity with Hard Water Ions:
1. Obtain two test tubes.
Into test tube #1 pour 5 mLs of the unpurified soap solution.
Into test tube #2 pour 5 mLs of detergent solution.
2. Add up to 10 drops of 1M Calcium Chloride (CaCl2), one drop at
a time, to each tube and observe if a precipitate forms.
3. Record the results.15
The sodium salts of
fatty acids, soaps, are
soluble in water. When
other metal ions like
calcium, magnesium, or
iron, form salts with
fatty acids they are not
as soluble in water and
tend to precipitate out.
16
D. Reactivity with Acid:
4. Obtain two test tubes.
Into test tube #1 pour 5 mLs of the unpurified soap solution.
Into test tube #2 pour 5 mLs of detergent solution.
5. Add up to 4 drops of 6M HCl (hydrochloric acid), one drop at a
time to each test tube and observe if a precipitate forms.
6. Record the results.16
106
15
CH110 Lab 9. Esters, Fats, and Soap (W14)
A soap is a weak base
so it reacts with HCl by
taking an H+ which
turns it into a carboxylic
acid. The newly made
carboxylic acid is a fatty
acid with a long
hydrocarbon chain and
now that it has no
charge it is no longer
soluble in water.
LAB 9. ESTERS & FATS:
NAME_____________
DATE______________
PRE LAB EXERCISES:
1. Match the following terms with the structures they represent:
_____ Ester
A.
O
H
O
H C
H C
O C
H C
H
_____ Fatty Acid
C
O
O
O
C
B.
O C
O
C
O
O
O
C O
O
C
O
O
C O
O C
_____ Triacylglycerol
O
O
C
O
C.
O
S
O Na
O
_____ Soap
D.
O
C
_____ Detergent
E.
H H O
H H
C
C O C C
H H
H H
H C
_____ Micelle
OH
H
F.
O
C
CH110 Lab 9. Esters, Fats, and Soap (W14)
O Na
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CH110 Lab 9. Esters, Fats, and Soap (W14)
LAB 9. ESTERS & FATS:
NAME___________________
PARTNER_________DATE___
REPORT:
I. PREPARATION OF ESTERS:
Complete the Equations:
Aroma:
(circle one)
Tube A
H O
H H
Banana
H+
H C C O H + H O C C H
H
Ethanoic Acid
Acetic Acid
Butter Rum
H H
Polish Remover
Ethyl Alcohol
Ethanol
Wintergreen
Name of Ester: IUPAC =
Common =
Tube B
O
C
Banana
H
O H
+
Butter Rum
H+
H C O H
Polish Remover
H
O H
Salicylic Acid
Wintergreen
Methyl Alcohol
Methanol
Name of Ester:
Tube C
H H H H H
H O
H+
H C C C C C O H + H C C O H
H H H H H
H
Pentyl Alcohol
Pentanol
Banana
Butter Rum
Polish Remover
Ethanoic Acid
Acetic Acid
Wintergreen
Name of Ester:
Tube D
O
C
Banana
H H
O H
+
H C C O H
H+
H H
Butter Rum
Polish Remover
Wintergreen
Benzoic Acid
Ethyl Alcohol
Ethanol
Name of Ester:
CH110 Lab 9. Esters, Fats, and Soap (W14)
109
II. SOAP:
Observations
pH
A. Preparation
Appearance of freshly made soap:
pH of crude soap
dissolved in
water:
_________
B. Purification
Results of “salting out” the soap:
pH of purified
soap dissolved in
water:
_________
pH of detergent
solution:
_________
Describe the “lather” after shaking:
Results of “salting out” detergent:
Results of adding CaCl2 to soap:
C. Reaction
with Hard
Water Ions
Results of adding CaCl2 to detergent:
Complete the reaction:
O
Na
9
O C
18
+ CaCl2
Sodium Oleate
Name of Products formed:
Results of adding to HCl soap:
D. Reaction
with Acid
Results of adding HCl to detergent:
Complete the reaction:
O
Na
O C
9
18
+ HCl
Sodium Oleate
Name of Products formed:
110
CH110 Lab 9. Esters, Fats, and Soap (W14)
LAB 9. ESTERS & FATS:
NAME_____________
DATE______________
POST LAB EXERCISES:
_____1.
“Salting” works to purify soap because _______.
A. Salt kills bacteria that would make soap impure.
B. Soap is not as soluble in water as salt is.
C. Salt (NaCl) undergoes a chemical reaction with soap to make a less soluble
product that can precipitate.
D. More than one of these.
_____2.
What is the advantage of using detergent instead of soap if you have “hard” water?
A. Detergent reacts with hard water ions to form new compounds that are soluble in
water.
B. Soap reacts with the ions in hard water and forms insoluble soap scum solids.
C. Detergent is cheaper than soap.
D. More than one of these.
_____3.
Soaps and detergents dissolve in both nonpolar oil and in polar water because ____
A. they have a nonpolar ionic end that attracts oil and a polar hydrocarbon end that
attracts water.
B. they have a nonpolar ionic end that attracts water and a polar hydrocarbon end
that attracts oil.
C. they have a polar ionic end that attracts water and a nonpolar hydrocarbon end
that attracts oil.
D. Soaps and detergents are neither polar nor nonpolar so the solvent doesn’t matter.
4. Complete the following:
O
C
H H
O H + H C C O H
H+
H H
Myristic Acid
5. Name the Products:
6..Complete the following:
O
H
O
C
H C
O
H C
O C
H C
O
H
O
NaOH
H2O
C
Glyceryl Trioleate
7. Name the Products:
CH110 Lab 9. Esters, Fats, and Soap (W14)
111
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CH110 Lab 9. Esters, Fats, and Soap (W14)