CHE XXXXXXXXXXManual 3E.pdf
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LABORATORY GOALS
LAB INFORMATION
Time: 3 h
Comments: Bromine can cause severe chemical burns. Use carefully.
Tear out the report sheets and place them beside the matching procedures.
Related Topics: Fatty acids, saturated and unsaturated fatty acids, lipids, triglycerides
Dispose of all chemicals as directed by your laboratory instructor.
CHEMICAL CONCEPTS
Lipids
Lipids are a family of biomolecules that have the common property of being soluble in organic solvents
lipos,
lipid family, there are specific structures that distinguish the different types of lipids. Lipids such as
waxes, fats, oils, and triacylphospholipids are esters that can be hydrolyzed to give fatty acids along with
the alcohol glycerol. Steroids, which have a completely different structure, do not contain fatty acids and
cannot be hydrolyzed. Steroids are characterized by the steroid nucleus of four fused ca
on rings.
Lipids are naturally occu
ing compounds that are soluble in organic solvents and not in water.
Lipids 31
350 Laboratory Manual for General, Organic, and Biological Chemistry
A. Physical Properties of 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 than in water.
Important types of lipids include fats and oils, glycerophospholipids, and steroids. Compounds classified
as lipids include fat-soluble vitamins A, D, E, and K; cholesterol; hormones; portions of cell mem-
anes; and vegetable oils. Table 31.1 lists the classes of lipids.
The structural formulas of three typical lipids are shown here:
B. Triacylglycerols
Fatty acids are long-chain ca
oxylic acids, usually 12 to 18 ca
ons in length.
The structural formula for lauric acid, a fatty acid, can be drawn in several ways.
TABLE 31.1 Classes of Lipid Molecules
Lipids Components
Waxes Fatty acid and long-chain alcohol
Fats and oils (triacylglycerols) Fatty acids and glycerol
Glycerophospholipids Fatty acids, glycerol, phosphate, amino alcohol
Sphingolipids Fatty acids, sphingosine, phosphate, amino alcohol
Steroids A fused structure of three cyclohexanes and a cyclopentane
Lipids 351
The triacylglycerols are esters of glycerol and fatty acids. When a fatty acid contains one or more
ca
on-ca
on double bonds, the triacylglycerol is refe
ed to as an unsaturated fat. When the fatty acid
consists of only ca
on-ca
on single bonds, the triacylglycerol is a saturated fat. Table 31.2 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 liquid. Fats that contain mostly saturated fatty acids have a
higher melting point than fats with more unsaturated fatty acids.
TABLE 31.2 Structures and Melting Points of Common Fatty Acids
Name Ca
on
Atoms
Source Melting
Point ( C)
Structures
Saturated Fatty Acids
Lauric acid 12 Coconut 44
Myristic acid 14 Nutmeg 55
Palmitic acid 16 Palm 63
Stearic acid 18 Animal fat 69
Monounsaturated Fatty Acids
Palmitoleic acid 16 Butter 0
Oleic acid 18 Olive, pecan,
grapeseed
14
Polyunsaturated Fatty Acids
Linoleic acid 18 Soybeans,
sunflowers
5
Linolenic acid 18 Corn 11
When glycerol reacts with stearic acid, the triacylglycerol that forms is glyceryl tristearate (tristearin).
352 Laboratory Manual for General, Organic, and Biological Chemistry
C. Bromine Test for Unsaturation
The presence of unsaturation in a fatty acid or a triacylglycerol can be detected by the
omine test,
which you used in an earlier experiment to detect double bonds in alkenes. If the orange color of the
omine solution fades quickly, an addition reaction has occu
ed and the oil or fat is unsaturated.
D. Preparation of Hand Lotion
Triacylglycerols are used to thicken creams and lotions.
Lotions are applied to the skin to soften, smooth, and hydrate the skin. The lotion contains compo-
nents soluble in water and oils, which are not soluble in water. A lotion is prepared by mixing the water
and oils to form an emulsion. Stearic acid and triethanolamine form a salt that helps emulsify the com-
ponents of the hand lotion. Glycerin is used to improve the texture of the lotion or cream. Lanolin is a
waxy substance that helps the skin abso
water.
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354 Laboratory Manual for General, Organic, and Biological Chemistry
EXPERIMENTAL PROCEDURES GOGGLES REQUIRED!
A. Physical Properties of Lipids and Fatty Acids
Materials: Test tubes and stoppers, dropper bottles or solids: stearic acid, oleic acid, olive oil, safflower
oil, lecithin, cholesterol, spatulas, 2 2CH Cl
1. To 6 separate test tubes, add 5 drops or the amount of solid lipid held on the tip of a spatula of
stearic acid, oleic acid, olive oil, safflower oil, lecithin, cholesterol. Classify each as a triacylglyc-
erol, fatty acid, steroid, or glycerophospholipid.
2. Describe the appearance of each.
3. Describe the odor of each.
May be done as a demonstration
4. Add about 2 mL of water to each of the test tubes. Stopper and shake each test tube. Record the
solubility of the lipids in water (a polar solvent).
May be done as a demonstration
5. In the hood: To 6 separate test tubes, add 5 drops or the amount of solid lipid held on the tip of a
spatula of stearic acid, oleic acid, olive oil, safflower oil, lecithin, cholesterol. Add 1 mL (20
drops) methylene chloride, 2 2CH Cl , to each sample. Record the solubility of the lipids in a nonpo-
lar solvent.
Save the test tubes and samples of stearic acid, oleic acid, olive oil, and safflower oil for Part C.
B. Triacylglycerols
Materials: Organic model kits or models
1. Use an organic model kit or look at prepared models of a molecule of glycerol and three molecules
of ethanoic acid. What are the functional groups on each?
2. Write the equation for the formation of the glyceryl triethanoate by drawing the condensed structural
formulas of the reactants and the products.
3. Write the equation for the hydrolysis of the glyceryl triethanoate by drawing the condensed structural
formulas of the reactants and the products.
C. Bromine Test for Unsaturation
Materials: Samples from Part A.5, 1% 2Br in methylene chloride
1. In the hood: To the samples of stearic acid, oleic acid, safflower oil, and olive oil from Part A.5,
add 1%
omine solution, drop by drop, until a permanent red-orange color is obtained or until 20
drops have been added.
Caution: Avoid contact with
omine solution; it can cause painful burns. Do not
eathe the
fumes.
Determine if the red-orange color fades rapidly or persists. Record your observations.
2. Indicate whether each sample contains a saturated or unsaturated lipid.
D. Preparation of Hand Lotion
Materials: Stearic acid, cetyl alcohol, lanolin (anhydrous), triethanolamine, glycerol, ethanol, distilled water,
commercial hand lotions, 100-mL graduated cylinder, 50-mL beaker, 100-mL beaker,
250-mL beaker for water bath thermometer, Bunsen burner, iron ring, wire screen or hot
plate, sti
ing rods, pH paper
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Copyright © 2014 Pearson Education, Inc. 357
Pre-Lab Study Questions 31
1. What is the functional group in a triacylglycerol?
2. Draw the skeletal formula of linolenic acid. Why is it an unsaturated fatty acid?
3. What type of solvent is needed to remove an oil spot? Why?
4. Write the equation for the esterification of glycerol and three palmitic acids.
Date Name
Section Team
Instructor
Copyright © 2014 Pearson Education, Inc. 359
REPORT SHEET
Lipids
LAB
31
A. Physical Properties of Lipids and Fatty Acids
Lipid 1. Type 2. Appearance 3. Odor 4. Soluble
in Water
(yes/no)
5. Soluble
in 2 2CH Cl
(yes/no)
Stearic acid
Oleic acid
Olive oil
Safflower oil
Lecithin
Cholesterol
Questions and Problems
Q1 Why are the compounds in Part A classified as lipids?
B. Triacylglycerols
1. Functional group of glycerol
Functional group of ethanoic acid
2. Equation for the esterification of glycerol and three ethanoic acids.
Date Name
Section Team
Instructor
360 Laboratory Manual for General, Organic, and Biological Chemistry
3. Equation for the hydrolysis of glyceryl triethanoate.
C. Bromine Test for Unsaturation
1. Color fades rapidly/persists 2. Saturated/Unsaturated
Fatty acids
Stearic acid
Oleic acid
Triacylglycerols
Safflower oil
Olive oil
Questions and Problems
Q3 a. Draw the condensed structural formulas of stearic acid and oleic acid.
Stearic acid
Oleic acid
b. From the results of Part C, which is more unsaturated: oleic acid or stearic acid?
Explain your reason.
c. From the results of Part C, were safflower oil and olive oil saturated or unsatu-
ated? Explain your reason.
Lipids 361
D. Preparation of Hand Lotion
1. Appearance
Hand Lotion (without triethanolamine) (without stearic acid)
2. pH
3. pH of commercial hand lotions
Brand ________________
pH ___________________
Brand ________________
pH ___________________
Brand ________________
pH ___________________
Questions and Problems
Q4 How does omitting triethanolamine affect the properties and appearance of the hand
lotion?
Q5 How does omitting stearic acid affect the properties and appearance of the hand
lotion?
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