Please help me to answer the pre-lab qouestions for the following lab: How Sweet
ID: 488178 • Letter: P
Question
Please help me to answer the pre-lab qouestions for the following lab:
How Sweet it is! Sensory Quality and Ester Synthesis
Reading: Why Fries Taste so Good: http://www.pbs.org/pov/foodinc/fastfoodnation_03.php
Nature contains a large number of compounds that smell sweet. Flowers and fruits, in particular, contain compounds whose aromas are pleasing. Chemists have separated, identified, and synthesized many of these compounds, making them available at a reasonable cost for use in cosmetics, household products, cleaners, and even foods. One common compound, ethyl acetate, is often used to remove nail polish.
These compounds are produced or synthesized by specific chemical reactions. One class of compounds that is usually sweet smelling is the esters. In fact, the main ingredient in artificial flavorings is an ester. Esters contain the functional group
where R1 and R2 are alkyl groups (groups that contain only carbon and hydrogen). The ester octyl acetate, which has the odor of orange peels, has an R1 = CH3 (methyl) and R2 = CH3(CH2)7 (octyl).
Octyl acetate
One method of producing esters is to react a carboxylic acid with an alcohol in an acidic medium. The acid acts as a catalyst. Below, the carboxylic acid acetic acid is treated with the alcohol ethanol to produce the ester ethyl acetate. The acid catalyst is shown as a "H+" over the arrow. Water is produced as a side product.
Acetic Acid Ethanol Ethyl Acetate
The name of esters is usually listed in two parts: The group attached to the oxygen is listed first (that group originated from the alcohol, in this case ethanol) with the “ol” ending switched to an “yl” ending. The second name originates from the acid name. Most acids have either an “ic” or an “oic” suffix; in the ester name, that suffix is replaced with either an “ate” or an “oate” suffix. Thus, the new ester above is named as ethyl acetate.
Through this lab we will explore the connection between functional groups and our senses as well as explore the synthesis of several esters.
Pre-lab
A.Basic Tastes: Complete the table below with appropriate entries for taste and smell sensations
Taste Sensation
Smell Sensation
Chemical substance present
Typical foods
Hydroxyl groups (OH)
Candy
Ions of salt
Pickled vegetables
Hydrogen ions (H+) in acids
Lemons
Amino Acids
Eggs, seafood, MSG*
Bitter
Alkaloids
Caffeine* and pure cocoa
*ingredient in foods and/or beverage
B.Read “Why do Fries Taste so good?” What did you find new in this article? What was most interesting to you?
C.In the article, Eric Schlosser states “Scientists now believe that human beings acquired the sense of taste as a way to avoid being poisoned.” How does that statement relate to the activity in Part A? Do you agree with the statement? Explain.
D.What role do you think the sense of smell plays? On an evolutionary standpoint, why do you think the sense of smell was developed?
E.Why is the flavor industry such an important aspect of foods?
Lab Procedure
A. Senses
B. Ester Synthesis
Today in lab you will be synthesizing seven different esters that are used in the food industry as well as identifying their odors and naming the esters. Combinations for esters are noted in the table below. You and a partner will work together to prepare seven new compounds.
Alcohol
Carboxylic Acid
Ester name
Scent
Ester 1
1-pentanol
(n-amyl alcohol)
Acetic acid
Ester 2
Ethanol (ethyl alcohol)
Formic acid
Ester 3
Methanol
(methyl alcohol)
Salicylic acid
Ester 4
Ethanol (ethyl alcohol)
Butyric acid
Ester 5
Butanol (butyl alcohol)
Acetic acid
Ester 6
1-pentanol
(N-amyl alcohol)
Butyric acid
Ester 7
Methanol
(methyl alcohol)
Butyric acid
CAUTION: concentrated sulfuric acid is highly corrosive and should remain in the hood. Glacial acetic acid and formic acid are also corrosive and should be added to testtubes in the hoods. Pentanol, ethanol, methanol, and butanol, and glacial acetic acid are flammable – NO OPEN FLAMES IN THE LABORATORY. Methanol is toxic and should be handled with gloves. Great care should be used when handling all these reagents. Goggles and gloves should be worn at all times.
Procedure
1.Fill a 250 or 500 mL beaker ~ ½ full water. Place beaker on hotplate and heat to 50-60 C while preparing the test tubes (as in #2-4).
2. Label 7 test tubes 1-7 using a Sharpie.
3.For each ester, add 1 mL alcohol and 1 mL carboxylic acid (or 1 scoop for salicylic acid) to the corresponding test tube.
4.Carefully add 3-4 drops of sulfuric acid to each test tube.
5.Carefully place test tubes in hot water bath (50-60 C) for 5-10 minutes.
6.Try to identify the odor of the ester. If the smell of sulfuric acid is too strong (how would that smell?), neutralize the acid with a few drops of 5% sodium bicarbonate.
7.Name the esters you synthesized.
8.Dispose of esters in the container marked “non-halogenated organic waste.”
Explanation / Answer
Esters contain the functional group,
R1-CO-O-R2
Prelab : A. Basic Tastes
Taste Smell Chemical present
bitter unpleseant hydroxyl (OH-)
salty depend of salt Ions of salt
bitter unpleseant hydronium (H+)
sour/sweet/bitter pungent amino acids
bitter irritant alkaloid
B. Ester synthesis
alcohol carboxylic acid Ester Name Scent
Ester 1 1-pentanol acetic acid pentyl acetate sweet
Ester 2 ethanol formic acid ethyl formate rum
Ester 3 methanol salicylic acid salicylic acid methyl ester minty
Ester 4 ethanol butyric acid ethyl butyrate fruity
Ester 5 butanol acetic acid butyl acetate sweet
Ester 6 1-pentanol butyric acid pentyl butyrate fruity
Ester 7 methanol butyric acid methyl butyrate sweet