Experiment 33- Lipids: Making Lotions
Goals
 Discuss physical and chemical properties of some common lipids.
 Draw the structure of a typical triacylglycerol
 Discuss the structures of saturated and unsaturated fats
 Prepare a hand lotion and determine the function of its
components.
Discussion
The triacylglycerols, commonly called fats or oils, are esters of glycerol
and fatty acids. Fatty acids are the long-chain carboxylic acids,
usually 14 to 18 carbons in length. When the fatty acid contains
double bonds, the triacylglycerol is referred to as an unsaturated fat.
When the fatty acid consists of an alkane-like carbon chain, the
triacylglycerol is a saturated fat. Table 33.1 below gives the formulas
of the common fatty acids and their melting points. At room
temperature, saturated fats are usually solid and unsaturated fats are
usually liquids (oils).
Table 33.1 Formulas, melting points and sources of some fatty acids
Carbon
Atoms
Structural
Formula
Melting
Point ˚C
Common
Name
Source
Saturated fatty acids(single carbon-carbon bonds)
12
14
16
18
CH3(CH2)10COOH
CH3(CH2)12COOH
CH3(CH2)14COOH
CH3(CH2)16COOH
44
54
63
70
lauric
myristic
palmitic
steric
coconut
nutmeg
palm
animal fat
Monounsaturated fatty acids(one cis double bond)
16 CH3(CH2)5CH=CH(CH2)7COOH
18 CH3(CH2)7CH=CH(CH2)7COOH
1
4
palmitoleic
oleic
butter fat
olives, corn
Polyunsaturated fatty acids(two or more cis double bonds)
18 CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
18 CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH
-5
-11
linoleic
linolenic
safflower,
Sunflower
corn
Fats that contain mostly saturated fatty acids have a higher melting
point than fats with more unsaturated fatty acids.
O
CH2OH
CH2O
O
+
CHOH
3 HO
CHO
C(CH2)14CH3
CH2OH
CH2O
Glycerol
3 palmitic acids
C(CH2)14CH3
O
+ 3 H2O
C(CH2)14CH3
C(CH2)14CH3
Glyceryl palmitate
(tripalmitin)
Figure 1: synthesis of a triacylglycerol from glycerol and palmitic acid.
O
Physical properties of some lipids and fatty acids
Lipids are a family of compounds that are grouped by similarities in
solubility rather than structure. As a group, lipids are more soluble in
nonpolar solvents such as ether, chloroform, or benzene. Most are not
soluble in water. Important types of lipids include fats and oil,
glycerophospholipids, and steroids. Compounds classified s lipids
include fat-soluble vitamins A, D, E, and K; cholesterol; hormones;
portions of cell membranes and vegetable oils. Table 33.2 lists the
classes of lipids.
Table 33.2 Classes of Lipid Molecules
Lipids
Components
Waxes
Fatty acid and long-chain alcohol
Fats and oils(triacylglycerols) Fatty acid and glycerol
Glycerophospholipids
Fatty acids, glycerol, phosphate, amino
alcohol
Steroids
A fused structure of three cyclohexanes
and a cyclopentane
The structural formulas of three typical lipids are shown below:
O
H3C
CH3
CH3
O
CH3
CH3
CH2O C(CH2)16CH3
O
CHO C(CH2)16CH3
CH2O
C(CH2)16CH3
CH3(CH2)14C
O(CH2)29CH3
Wax
HO
O
Cholesterol, a steroid
Triacyl glycerol, a fat
Figure 2: Structures of typical lipids: A steroid (left); A triglyceride (center); A wax
(right).
Preparation of Hand lotion
We use hand lotions and creams to soften our skin and reduce
dryness. Typically, the formulation of a hand lotion consist of several
components such as steric acid, lanolin, triethanolamine, cetyl alcohol,
glycerin (glycerol), water, and usually a fragrance. Lanolin from wool
consists of a mixture of waxes.
Because lipids are non-polar, they protect and soften by preventing
the loss of moisture from the skin. Some of the components help
emulsify the polar and nonpolar ingredients. In this experiment we
will see how the physical and chemical properties of lipids are used to
prepare a hand lotion.
Lab Information
Materials: Stearic acid, cetyl alcohol, lanolin, triethanolamine,
glycerol, ethanol, distilled water, fragrance (optional), commercial
hand lotions, 10-mL graduated cylinder, 50-mL graduated cylinder,
two 100-mL beakers, thermometer, 250-mL beaker for water bath, hot
plate, stirring rod, tongs, pH paper.
Obtain the following substances and combine in two 100-mL beakers.
Use a laboratory balance to weigh out the solid substances. Use a 10mL graduated cylinder to measure glycerin; use a plastic pipet with
gradient for Triethanolamine; use a 50-mL graduated cylinder to
measure larger volumes.
Beaker 1
Stearic acid
Cetyl alcohol
Lanolin
Triethanolamine
3g
1g
2g
1mL
Beaker 2
Glycerin 2 mL
Water
50 mL
Water bath: Fill two 250-mL beakers about 2/3 full with water. Place
the beakers on a hot plate and heat the water to just below boiling.
 Using a pair of crucible tongs, hold beaker 1 (four ingredients) in
the water bath and heat to 80˚C or until all the compounds have
melted. Make sure all compounds stay dissolved.
 Using a pair of crucible tongs, hold beaker 2 (two ingredients) in
the second water bath and heat to 80˚C.
 Remove beakers from heat. While still warm, slowly pour the
glycerol-water mixture from Beaker 2 into Beaker 1 as you stir.
If your lotion is too thick, add 5.0 mL of ethanol and a few drops
of fragrance, if desired.




Continue to stir for 3-5 minutes until a smooth creamy lotion is
obtained. If the resulting product is too thick, add more warm
distilled water.
Using pH paper and a stirring rod, obtain the pH of your lotion.
For comparison, take the pH of at least 2 commercial hand
lotions provided as well. Create a table to show your data.
Package your lotions into the provided plastic baggie or in a
bottle from home. Remember that lotions spoil after about 9
months of preparation with out preservatives. The lotion you
have prepared today contains no preservatives. To extend the
life of your lotion, you may add some vitamin E (about 5 drops is
good).
Pre-lab Questions
1. Make a table with the physical and chemical properties of the
ingredients for the preparation of lotion. (Molecular mass,
chemical structure, m.p, b.p., density, solubility in water,
flammability, and toxicity/hazards).
2. Draw the Lewis structure of each ingredient for the preparation
of lotion. Label each functional group present.
3. Classify each ingredient for the preparation of lotion using table
33.2. Briefly explain your choices for classification.
4. Create a flow-chart for the experiment. This will be your
procedures.
In-lab Questions
1. Report the pH of your hand lotion and the commercial hand
lotions available. Discuss what pH range is safe for use with
lotions.
2. Report the quantity of lotion obtained (by volume). Suggest
ways to increase the yield of lotion for the experiment.
3. Describe the smoothness and appearance of the hand lotion.
Compare with a commercial lotion (provide name and
manufacturer).
4. Speculate on the function of each ingredient in the preparation
of hand lotion.
5. How would eliminating triethanolamine affect the consistency of
the hand lotion?
6. How would eliminating steric acid affect the consistency of the
hand lotion?