Download testing for organic functional groups lab

Austin Peay State University Department of Chemistry
CHEM 1021
TESTING FOR ORGANIC FUNCTIONAL GROUPS
Caution: Chromic acid is hazardous as are many of the organic substances in today’s experiment. Treat
all unknowns with extreme care. Many organic substances are flammable.
Purpose: In this lab you will use traditional chemical tests to identify a variety of functional groups in
known chemicals, and to use those positive results to identify the functional groups present in an
unknown chemical.
Background: Chemists today are trained to use elaborate technologies and instrumentation to
determine chemical structure and makeup. However, many years ago, these technologies were not yet
available, and there were very few ways for chemists to determine the composition of any chemical.
Chemists would use a series of tests to characterize the structure and makeup of a chemical. You will
be doing some of these tests in this lab, in particular, ones that indicate functional groups present on a
molecule.
Functional groups can be defined as the parts of organic molecules that are prone to chemical reactions.
Molecules with carbon chains full of hydrogens (saturated hydrocarbons), are not especially susceptible
to reactions, but chemicals that contain oxygen, nitrogen, halogens (Br, Cl, F, and I) and multiple bonds
between carbon atoms can react quite easily in specific conditions. The following functional groups will
be tested in this experiment:
•
Alkenes—alkenes are chemicals that contain a carbon-carbon double bond. They react with the
magenta-colored chemical potassium permanganate (KMnO4) to product manganese dioxide
(MnO2), which is a brown solid. In other words, you can determine if a chemical has a double
bond by adding KMnO4 and looking for the development of the brown solid MnO2.
Example: 1-butene
OH
H3C
H2
C
CH2
C
H
KMnO4
H2
C
H3C
H
C
CH2
+
MnO2(s)
OH
•
Alcohols—alcohols consist of a hydroxyl group (-OH) attached to a carbon chain. Alcohols are
oxidized with chromic acid (H2CrO4) to give a carbonyl (C=O) and a green chromium compound
(a chromium oxide). Positive identification of an alcohol will be evident when the addition of
chromic acid results in a green solution. This reaction is quick, working on the order of 2-3
seconds. Aldehydes also react with chromic acid to produce the green chromium compound,
but the reaction takes a bit longer, 10-12 seconds or so.
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Austin Peay State University Department of Chemistry
CHEM 1021
Example: 2-propanol (iso-propanol)
•
Ketones/aldehydes—a carbon-oxygen double bond, where the carbon is also attached to two
other carbons (ketone) or to a carbon and a hydrogen (aldehyde). Ketones and aldehydes react
with a chemical called 2,4-dinitrophenylhydrazine (2,4-DNPH) to form a yellow or orange solid
within a few minutes.
Example: propanone (a ketone)
Example: ethanal (an aldehyde)
NO2
H
NO2
H
N
CH3
NH2
C
O2N
C
N
+
O
CH3
H
N
H
O2N
2,4-DNPH
•
Alkyl halides—alkanes that have a halogen in place of a hydrogen. Bromines, chlorines, and
iodines attached to carbons are all alkyl halides. It is quite easy to test for halogens on an
organic compound by way of a Beilstein test. A copper wire can be heated under a flame to
from a layer of copper II oxide (CuO) on the wire. Dipping the coated wire in your compound to
coat it, and put it under the flame. A green flame indicates the burning of a copper halide,
which shows a reaction between an alkyl halide and the copper oxide.
Example: methyl bromide
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Austin Peay State University Department of Chemistry
Equipment:
Copper wire
Bunsen burner
Spatulas
Disposable pipettes
Chromic acid reagent
Methylene Chloride
Unknown chemicals
2% KMnO4(aq)
Acetone
2,4-DNPH reagent
CHEM 1021
Hexane standard
Test tube rack
Sand paper
Small test tubes/stoppers
Pentene
Hexanal
Ethanol
Procedure: This experiment will consist of adding chemicals to test tubes. You will want to keep track
of each test tube, and keep them until the end of the experiment for comparison to your unknown
chemical.
I. Testing for alkenes: Set up two test tubes in the test tube rack. In tube one, put in 4 drops of hexane.
In tube two, put in 4 drops of pentene. Add 2 mL of ethanol to each tube. Add two drops of the
permanganate solution, stopper, and shake (be careful you know which tube is which!) Record the
results on the data sheet.
II. Testing for alcohols: Set up two new test tubes in the test tube rack. In tube one, put in 1 drop of
hexane, and in tube two put in one drop of ethanol. Add 1 mL of acetone to each tube followed by 1
drop of the chromic acid reagent. Gently swirl the tubes. Record the results on the data sheet.
III. Testing for ketones: Set up two test tubes in the test tube rack. In tube one, put in 2 drops of
hexane, and in tube two, put in 2 drops of acetone. Add 2 mL of ethanol to each tube followed by 3 mL
of the 2,4-DNPH reagent. Stopper and shake well. Let the solution stand for up to 15 minutes. You can
go onto the next test in this time. Record the results on the data sheet.
IV. Testing for aldehydes: You will be using two tests for aldehydes, the chromic acid test as well as the
2,4-DNPH test. Because you already know what the negative tests for these look like, you will only be
doing the positive tests. Set up two test tubes in the test tube rack. In tube 1, put in 1 drop of hexanal,
1 mL of acetone, and 1 drop of chromic acid. Swirl the tube. In tube 2, put in 2 drops of hexanal, 2 mL
of ethanol, and 3 mL of the 2,4-DNPH reagent. Stopper and shake the tube. Wait up to 15 minutes for a
reaction in tube 2. Compare the tests to the positive and negative tests in 2 and 3 above. Record the
results on the data sheet.
V. Testing for alkyl halides: Take a small length of copper wire and brush it clean using the sand paper.
Hold it over a flame for about 30 seconds. Take it out of the fire and let it cool down. Dip the wire in
hexane and hold over the flame. Repeat the procedure using methylene chloride. Record the results on
the data sheet.
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Austin Peay State University Department of Chemistry
CHEM 1021
VI. Testing your unknown: Obtain your unknown and 3 test tubes. Do the alkene, alcohol/aldehyde,
and aldehyde/ketone test on it as well as the alkyl halide test. Record your results on the data sheet.
Compare to the positive results for the known chemicals above to determine the functional groups
present in your compound.
Waste Disposal and Cleanup: When you are finished, pour the chemicals in the appropriate waste
container. Wash your glassware thoroughly with soap and water followed by a distilled water rinse.
*Techniques and Experiments for Organic Chemistry
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Austin Peay State University Department of Chemistry
CHEM 1021
TESTING FOR ORGANIC FUNCTIONAL GROUPS DATA SHEET
Name: _____________________________________
Partner: ____________________________________
Unknown #:_________________________________
I.
Alkene test
a. Hexane control observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
b. Propene observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
II.
Alcohol test
a. Hexane control observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
b. Ethanol observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Austin Peay State University Department of Chemistry
III.
CHEM 1021
Ketone test
a. Hexane observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
b. Acetone observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
IV.
Aldehyde tests
a. Chromic acid test observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
b. 2,4-DNPH test observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Austin Peay State University Department of Chemistry
V.
CHEM 1021
Alkyl halide test
a. Hexane observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
b. Methylene chloride observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
VI.
Unknown tests:
a. Alkene test observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Is this test positive or negative? _________________________________
b. Alcohol/aldehyde test observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Is this test positive or negative? _________________________________
c. Ketone/aldehyde test observations:
________________________________________________________________________
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Austin Peay State University Department of Chemistry
CHEM 1021
________________________________________________________________________
________________________________________________________________________
Is this test positive or negative? _________________________________
d. Alkyl halide test observations:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Is this test positive or negative? _________________________________
Which functional groups are present in your unknown chemical?
___________________________________________________________________________
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Austin Peay State University Department of Chemistry
CHEM 1021
TESTING FOR ORGANIC FUNCTIONAL GROUPS POST-LAB
Name:________________________________
Imagine you have 3 separate chemicals, an aldehyde, an alcohol, and a ketone. How could you
determine the functional group of each chemical? Explain.
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Using what you have learned in this lab, is there a way to distinguish between a chemical that has an
alcohol functional group and a chemical that has an aldehyde functional group on it? Explain.
_____________________________________________________________________________________
_____________________________________________________________________________________
What about one that has an aldehyde and one that has a ketone? Explain.
_____________________________________________________________________________________
_____________________________________________________________________________________
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Austin Peay State University Department of Chemistry
CHEM 1021
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Austin Peay State University Department of Chemistry
CHEM 1021
TESTING FOR ORGANIC FUNCTIONAL GROUPS PRE-LAB
Name:________________________________
1. Name and circle the functional groups below. Which test would you use for the following
chemicals?
_________________________________
_________________________________
_________________________________
_________________________________
_________________________________
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CHEM 1021
2. Draw the Lewis-dot structures below of chemicals that you will be using in this lab, circle the
functional group, and name the functional group.
Hexane:
Acetone:
Propene
Ethanol:
Hexanal
Methylene chloride:
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